Night blindness. Causes. Symptoms Diagnostics. Treatment. Night blindness is a disease in humans Rabbit ears ram

Hereditary retinal diseases- a clinically and genetically heterogeneous group of conditions: many of them manifest in childhood as an isolated anomaly in a practically healthy child. Some develop against the background of systemic anomalies. Most of the genes causing major retinal dystrophies in children have been identified, and complex relationships between genotype and phenotype have been identified. There is pronounced genetic heterogeneity in individual cases of genetic diseases; a mutation of one gene can cause the development of several different phenotypes. Despite this, these diseases can be classified according to the following criteria:
1. Stationary or progressive
2. Manifested by damage predominantly to rods or cones.

Stationary diseases manifest at birth or in the first months of life and are most accurately described as dysfunction syndromes. Progressive conditions, usually appearing later, are called dystrophies.

Stationary retinal dysfunction syndromes group of diseases includes various forms of stationary night blindness (rod dysfunction syndromes) and cone dysfunction syndromes (stationary cone diseases).

Highlight three main forms of stationary night blindness; with congenital stationary night-blindness (CSNB), the fundus of the eye is intact or changes characteristic of myopia develop. With fundus albipunctatus and Oguchi's disease, a characteristic pattern of changes in the fundus is observed.

A) Clinical manifestations. Congenital stationary night blindness is characterized by night blindness, varying degrees of visual impairment and the absence of changes in the fundus. It can be inherited through an autosomal dominant (AD), autosomal recessive (AR) or X-linked (XL) mechanism.

Visual acuity with an autosomal dominant form usually within normal limits or slightly reduced, while in autosomal recessive and X-linked forms there is a slight or moderate decrease in central visual acuity. Other manifestations of the X-linked and autosomal recessive form include moderate to high myopia, nystagmus, strabismus, and paradoxical pupillary reactions. When examining the fundus, no pathological changes are usually detected; some patients may experience changes characteristic of myopia, pallor, or tilting of the optic disc.

In patients with autosomal dominant congenital stationary night blindness the disease usually presents with symptomatic nyctalopia, but in the X-linked and autosomal recessive form the disease usually manifests in infancy with nystagmus, strabismus, and blurred vision. Nystagmus is not present in all patients, which leads to late diagnosis of the disease in childhood or even adulthood. Without electroretinography (ERG), the disease may remain undiagnosed. X-linked and autosomal recessive variants can be further subdivided into complete and incomplete forms. Initially, such differentiation based on electrophysiological and psychophysiological criteria was proposed for the X-linked form, and subsequently it was shown that this classification separates two genetically distinct diseases.

b) Electrophysiology of congenital permanent night blindness. Electroretinography should be performed according to the standards of the International Society for Clinical Electrophysiology of Vision (ISCEV). When examining infants, the study may not be feasible; in such cases, a modified protocol is used. Four main responses are determined: the rod ERG and the bright flash response under scotopic conditions, and two measures of cone function, the rhythmic ERG when stimulated by 30 Hz flicker and the ERG when stimulated by a single flash under photopic conditions.

And when full, and in the incomplete form of congenital stationary night blindness, a “negative ERG” is determined: the indicators of the a-wave generated by photoreceptors in response to a bright flash are normal, but there is a selective decrease in the b-wave generated by the cells of the inner nuclear layer, its amplitude becomes less than a- waves, which primarily indicates dysfunction of the inner layers of the retina. In complete congenital stationary night blindness, there is no rod ERG; upon stimulation with a bright flash, a deeply negative response is recorded.

On the cone ERG minor abnormalities are recorded, reflecting dysfunction of bipolar ON cells. In incomplete congenital stationary night blindness, a rod ERG and a profoundly negative response to a bright flash are generated. The cone ERG is much more altered than in the complete form of congenital stationary night blindness, indicating damage to both ON and OFF bipolar cells. When stimulated by flicker, a characteristic triphasic response is recorded.

With an autosomal dominant form congenital stationary night blindness changes indicating dysfunction of the intrinsic elements of the rod system may occur, but in combination with a normal cone ERG according to ISCEV protocols. In other cases of an autosomal dominant form of the disease, rod ERG responses are weakened, cone responses are within normal limits, but stimulation with a standard bright flash does not produce a negative wave.

V) Molecular genetics and pathogenesis of congenital stationary night blindness:

1. Autosomal dominant congenital stationary. In autosomal dominant congenital stationary night blindness, mutations have been described in genes encoding three specific components of the rod phototransduction cascade: rhodopsin, the α-subunit of rod transducin, and the β-subunit of phosphodiesterase (3-subunit-PDE P) of cyclic guanosine monophosphate (cyclic guanosine monophosphate). cGMP) rods.

2. X-linked congenital stationary night blindness. Two responsible genes have been identified (CACNA1F and NYX), and their defects cause the disease in most families. Incomplete congenital stationary night blindness develops against the background of a mutation in CACNA1F, which encodes a specific a1F subunit of the voltage-dependent L-type calcium channel of the retina. CACNA1F expression appears to be restricted to photoreceptors and expressed at synaptic terminals. Most mutations are sequence variants that cause premature termination of protein synthesis. The insufficiency of functioning rod and cone channels disrupts the supply of calcium to the photoreceptors, which is necessary for the tonic release of the neurotransmitter from the presynaptic endings.

This makes it impossible to maintain the normal transmembrane potential of bipolar cells, thus, in low light conditions, the retina is unable to respond to changes in illumination.

The full form of congenital stationary night blindness is caused by a mutation in NYX, the gene encoding the leucine-rich nyctalopia proteoglycan. Leucine-rich sequences are thought to play an important role in protein interactions, and many mutations have been identified within these sequences. Nyctalopia is expressed in the inner segment of photoreceptors, outer and inner nuclear layers and ganglion cells. Perhaps nyctalopia regulates and stimulates the formation and functioning of ON pathways in the retina.

Several studies of genotype-phenotype relationships have been conducted in patients with CACNA1F and NYX mutations. With CACNA1F mutations, pronounced interfamilial and intrafamilial phenotypic variability was observed, even with identical sequence variants, which indicates the influence of other genetic and environmental factors on the phenotype. Although most patients with X-linked congenital night blindness did not progress to disease progression, Nakamura et al. described two brothers with a CACNA1F mutation, progressive visual deterioration and, in the terminal stage of the disease, unrecordable rod and cone ERGs. Rarely, we have also observed slow disease progression in patients with X-linked congenital stationary night blindness.

Patients with complete congenital stationary night blindness (NYX mutations) always have myopia and much more severe nyctalopia.

3. Autosomal recessive congenital stationary night blindness. Mutations in GRM6 and TRPM1 cause a complete form of congenital stationary night blindness. GRM6 encodes a metabotropic glutamate receptor (mGluR6) of the dendrites of rods, cones and ON bipolar cells, which is involved in the change of sign (potential) at the first synapse, thus the release of glutamate by photoreceptors in the dark causes hyperpolarization of the membrane of the ON bipolar cell. TRPM1, transient receptor voltage-gated cation channel, subfamily M member 1, appears to influence ON bipolar cell membrane potential changes in response to glutamate.

Mutations SAVR4 cause an incomplete form of congenital stationary night blindness. CABP4, which belongs to the family of calcium-binding proteins (CABP), is localized exclusively at the synaptic terminals of photoreceptors, where it is directly associated with the C-terminal domain of CACNA1F.

Sequence variants in SLC24A1 have been identified in patients with autosomal recessive congenital stationary night blindness in the absence of negative ERG; with standard stimulation with a bright flash under scotopic conditions, the same decrease in the amplitude of a- and b-waves was recorded. SLC24A1 belongs to the superfamily of solute transport proteins and is localized in the inner segments (photoreceptors), outer and inner nuclear layers and ganglion cells.

4. Ophthalmopathy of the Åland Islands. Aland Island eye disease (AIED) is an X-linked recessive disease similar to incomplete congenital night blindness, characterized by decreased visual acuity, nystagmus, nyctalopia, mild red-green dyschromatopsia and myopia. Affected men may exhibit translucent iris, hypoplasia of the fovea, and hypopigmentation of the fundus. The clinical picture may resemble that of X-linked ocular albinism (XLOA), but in X-linked ocular albinism color perception is usually normal, and patients with Åland Islands ophthalmopathy do not exhibit the chiasmal nerve fiber abnormality characteristic of albinism.

Night blindness, psychophysical and ERG changes in Åland Islands ophthalmopathy are similar to those observed in incomplete X-linked congenital stationary night blindness. Both diseases are mapped in the same Xp zone: they are probably allelic to each other, but CACNA1F mutations have not been identified in Aland Islands ophthalmopathy.

5. Other related phenotypes. Patients with syndromes caused by adjacent gene abnormalities (including glycerol kinase deficiency, congenital adrenal hypoplasia, Duchenne's muscular dystrophy (DMD), and an eye abnormality known as Oregon ophthalmopathy) and Xp21 deletion have the same eye defects as men with Åland Islands ophthalmopathy and the same changes on the ERG, indicating damage predominantly to the inner layers of the retina. Moreover, some men with isolated Duchenne muscular dystrophy (mutation of the dystrophin gene on Xp21) show the same ERG changes as in congenital stationary night blindness. All of these multisystem disorders are accompanied by non-progressive dysfunction of the retina, predominantly of the rods.

20-11-2013, 03:18

Description

First type CSNB (Riggs type, Nougare type) CSNB Riggs type is inherited in an autosomal recessive sex-linked manner. Visual acuity may be slightly reduced, but in most cases it is normal. The field of view under photopic conditions is not changed. The fundus is normal. This type of CSNB is characterized by the absence or significant decrease in the amplitude of the scotopic ERG and the maximum ERG to a standard flash after dark adaptation, while both the a-wave and b-wave are reduced, reflecting the functions of photoreceptors and bipolars, respectively. Photopic ERG latency is approaching normal. The dark adaptation curve is monophasic with the absence of the cone-rod “heregib”, which is due to a significant decrease in the function of the rod system. In CSNB type Nougare with an autosomal dominant type of inheritance, a defect in the β-subunit of rod transducin (C1y38Acr) was noted. At the same time, significantly reduced rod components and slightly reduced cone components are recorded in the subnormal ERG, although some studies have noted the absence of rod function with normal cone function.

In Nuclear CSNB, the sensitivity of rod photoreceptor cells in the dark is reduced, which is due to a phototransduction defect associated with impaired enzyme function, which leads to a decrease in the amplitude of the ERG a and b waves under scotopic conditions, while during light adaptation the retina functions normally. The preservation of the function of the cone system is indicated by normal cone and rhythmic (30 Hz) ERG with normal visual acuity. However, cone and rhythmic ERG may be decreased. With this form of CSNB, the concentration of rhodopsin, its spectral characteristics and recovery kinetics, according to reflectometry, are normal.

It is assumed that in the first type of CSNB, the dysfunction of the rod system is explained by the pathology of phototransduction at one or more of its stages in the outer segments of the rod photoreceptors.

Second type CSNB (Schubert - Bornschein type) . The fundus is not changed, but a mild metallic reflex is possible in the middle part of the fundus and in the periphery.

Type CSNB Schubert - Bornschein characterized by the absence or significant decrease in the COLLAR and rod components of the L-wave of the maximum ERG. The absence or decrease of the b-wave leads to an increase in the amplitude of the a-wave compared to the norm, in this case a minus-negative ERG is recorded. In patients with CSNB combined with myopia, the a-wave is reduced, but not as significantly as the b-wave.

The content and density of visual pigment of rods in situ in patients with CSNB of the Schubert-Bornschein type are normal, which correlates with a normal ERG a-wave. The kinetics of rod photopigment regeneration is also within normal limits, which indicates that the photoreceptors are intact and the presence of a primary defect not in their outer segments, but in the transmission of the visual signal. Judging by the unchanged a-wave and subnormal b-wave, the pathological link in CSNB of the Schubert-Bornschein type is located in the proximal photoreceptors. The similarity of the negative ERG and ERG to a long-term stimulus with the ERG obtained in a live experimental model (in a macaque) with blocking of synapses of depolarizing bipolars with 2-amino-4-phosphonobutyrate (APB) suggests a violation of synaptic transmission from rod photoreceptors to rod bipolars and damage at the level of bipolar synapses of both the cone system (on-channels) and the rod system, consisting exclusively of on-channels. Changes in the functions of the cone system are indicated by the presence of subnormal photopic ERG, with reduced visual acuity.

Analysis of the genetic tree of patients and the identification of various functional disorders in them allowed Y. Miyake (1986) to identify two subtypes of CSNB of the Schubert-Bornschein type: complete - with the absence of the function of the rod system and incomplete - with the presence of its residual function. Both subtypes are characterized by a slight decrease in the function of the cone system.

Full type inheritance form CSNB - X-linked, in most cases the disease is combined with moderate and high myopia, often with nystagmus and amblyopia. This type of CSNB is characterized by the absence of themes of new adaptation and scotopic ERG. Visual acuity is reduced ( 0,8-0,1 ). Boundaries of the field of view during quantitative perimetry for objects V- 4 And 1-4 normal, but narrowed to object I. In the maximum ERG, a slightly reduced a-wave and a largely reduced b-wave are observed. When using a long-term stimulus, a CSNB pattern is revealed in the ERG with preservation of the off-components of the cone system and the absence of op-components. The amplitude of the cone ERG and rhythmic (30 Hz) ERG was significantly reduced after 30 min of dark adaptation and increases again with light adaptation. The kinetics of rhodopsin reduction and its amount are normal.

In CSNB with full gene penetrance, the absolute psychophysical threshold is determined primarily by the cone system. While the rod ERG to a weak short-wave (blue) stimulus is absent, the cone ERG is slightly reduced, i.e. Barrel photopic ERG is intact or subnormal. The cone-rod response is a negative ERG with a preserved a-wave and a significantly reduced b-wave, which is smaller in amplitude than the a-wave. With this type of CSNB, reduced oscillatory potentials are recorded. The EOG light rise is normal.

With incomplete Schubert-Bornschein type CSNB residual function of the rod system is observed. This type is also characterized by an X-linked recessive type of inheritance. Dark adaptation differs from the norm by increasing thresholds by 1,0-1,5 log.el., the absolute threshold is higher than normal, rods participate in its formation. The scotopic ERG is recorded, its amplitude is reduced, the weak blue stimulus rod component, although reduced, can be measured, while the cone ERG is significantly subnormal. In this type of CSNB, the rod system is less affected, oscillatory potentials are recorded more often, and the function of the cone system is reduced to a greater extent than in CSNB with complete gene penetrance. The ratio of the b-wave amplitude to the a-wave amplitude is greater than with the full Schubert-Bornschein CSNB type. With incomplete non-strangeness of the gene after 30 minutes of dark adaptation, flicker amplitude ( 30 Hz) ERG is increased, under conditions of light adaptation the waveform is changed. The main defect is proposed to be at the level of synaptic transmission between photoreceptors and depolarizing bipolars, which determines the pathological response of the rod and cone systems in the ERG.

Histological studies of the retina in both forms of CSNB did not reveal its structural changes.

Carriers of a pathological gene. Identification of carriers of the pathological CSNB gene is important not only for studying the phenotypic manifestations of rhodopsin gene mutations, but also for genetic consultations. Electroretinography is a fairly sensitive method for identifying the initial functional symptoms of hereditary pathology and the intermediate state between normal and pathology, which can be detected in patients without gene expression.

Not every type of CSNB inheritance can be identified as carrier of the gene. The disease, linked to the X chromosome, manifests itself in males and is transmitted through the maternal line. If there is a hereditary history in the family, a decrease in any visual function in a woman is confirmation of the carriage of a pathological gene. However, normal results of functional studies indicate either that the woman has inherited an X chromosome with a normal gene, or that she has inactivated a pathological X chromosome.

Congenital stationary night blindness with changes is glagiogonous. Ogushi's disease. In 1907, S. Oguchi discovered an unusual form of CSNB, in which decreased vision at night was detected already in early childhood. The fundus of the eye in this form of the disease has a gray-white color (decoration) with a metallic sheen, the vessels protrude in relief against a gray background, and the macular area looks dark compared to the surrounding tissues (Fig. 6.5).

The disease is characterized by yellowish phosphorescence of the fundus, similar to decoloration, most often on the periphery of the retina. In most cases, the fundus becomes normal after the patient remains in the dark for several hours. After exposure to photopic conditions, a metallic sheen gradually reappears in the retina. This phenomenon, discovered back in 1913 by Mizuo, is called the Mitsuo-Nakamura phenomenon.

Kinetics of rhodopsin, including both concentration and regeneration, is normal. During long-term dark adaptation, most patients with Ogushi disease experience an increase in the dark adaptation threshold with normal or slightly reduced ERG. The latency (imlicit time) of the rod and cone b-waves of the ERG is normal, but when the retina is stimulated with red light, the latency of the rod b-wave is prolonged.

In Ogushi disease, mutations have been identified in the gene encoding arrestin (retinal S-antigen) and rhodopsin kinase. The nature of the disturbance in background sensitivity in the Mitsuo-Nakamura phenomenon is unknown, but it is assumed that the normal processes of dark adaptation are combined in these patients with the pathological function of post-receptor cellular elements responsible for the generation of the ERG b-wave, which is confirmed by a decrease in the a-wave at high intensity of stimulating light .

There are two types of Ogushi's disease depending on the achievement of the thresholds of the dark adaptation curve: the first - in the presence of the Mitsuo-Nakamura phenomenon, the thresholds of the dark adaptation curve are reached; the second - the thresholds of the dark adaptation curve do not decrease regardless of its duration: the Mitsuo-Nakamura phenomenon occurs, the Mitsuo-Nakamura phenomenon is absent.

The function of the rod system is reduced: The scotopic ERG is subnormal when averaging signals during dark adaptation, although the first response to a bright flash under scotopic conditions is of normal amplitude. The maximum ERG is reduced, the photopic ERG is normal. In the ERG to a long-term stimulus, no changes in on- and off-responses were detected.

In Ogushi disease of the first type, which occurs most frequently, the period of time during which the thresholds of the dark adaptation curve are reached is increased (from 2 before 24 h). In the second type, the thresholds do not decrease below the cone thresholds, and the dark adaptation curve is monophasic. The results of dark adaptation do not depend on the presence of the Mitsuo-Nakamura phenomenon: it can be observed in forms with both monophasic and biphasic curves.

Due to the unusual color of the fundus and the presence of a pathological dark adaptation curve, many authors assumed that the cause of functional pathology was an abnormality in the kinetics of rhodopsin due to a slowdown in its synthesis. However, clinical studies have shown that the amount, regeneration and absorption spectrum of rhodopsin are normal in this form of stationary night blindness. Visual acuity is normal or slightly reduced EOG is normal. Fluorescein angiography reveals diffuse hyperfluorescence of the light-adapted retina.

Ogushi's disease should be differentiated from congenital stationary night blindness with a normal fundus. The characteristic ophthalmoscopic picture with a metallic luster of the fundus is the main criterion that allows a diagnosis of Ogushi's disease to be made with the symptom of night blindness.

Fundus albipunctatus (fundus albipunctatus) N. Lauber in 1910 identified fundus albipunctatus as an independent disease with an autosomal recessive mode of inheritance and differentiated it from albipuncata retinitis, similar in its ophthalmoscopic picture (retimts punclata albescens), which is one of the forms of progressive retinitis pigmentosa. the fundus is characterized by non-progressive stationary night blindness with a typical fundus picture for this pathology, represented by multiple discrete white dots of the same size of irregular shape, which sometimes have a comet configuration, but are so small that they are sometimes difficult to distinguish with indirect ophthalmoscopy. These points are located at the level of the pigment epithelium along the middle periphery of the retina and paramacularly and do not affect the foveal and parafoveal areas (Fig. 6.6)

They have no connection with retinal pigmentation or atrophy of the pigment epithelium. The optic nerve head and vessels are not changed, there is no accumulation of pigment clumps on the periphery. The time to reach the threshold of rod and cone dark adaptation is increased and for rods is 45 min. In some patients, complete dark adaptation cannot be achieved and thresholds always remain elevated at 3-4 log. ate, as in generalized retinal degeneration.

The amplitude of the scotopic ERG is variable: from normal to subnormal and minus-negative. ERG and EOG reach normal values ​​during dark adaptation, but over a longer period of time than normal, which corresponds to a slowdown in the regeneration of visual pigment and the process of reaching the psychophysical threshold of dark adaptation. The cause of these disorders is considered to be the presence of defects in the regeneration cycle of visual pigments, both cone and rod. With this form of CSNB, a significant slowdown in the regeneration of visual (rod and cone) pigments was revealed: the regeneration time of rhodopsin is on average 60 minutes (normally 3 minutes), the regeneration of cone pigments is 20 minutes (normally 75 s). At the same time, in patients with fundus albipunctatus, a normal level of vitamin A in the blood serum is detected and there is no systemic deficiency.

Patients with fundus albipunctatus have mutations in the gene encoding 11-cis-retinollehydrogenase. This microsomal enzyme is found in large quantities in the retinal pigment epithelium, where it serves as a catalyst for oxidative reactions converting 11-cis-retinol to 11-cis-retinal. A decrease in the activity of this enzyme is manifested in slower regeneration of visual pigment.

Fluorescein angiography
(FA) allows you to identify spots of hyperfluorescence that are not associated with the distribution of changes visible ophthalmoscopically; multiple small fenestrated pigment epithelial defects (white spots) in the midperiphery, in contrast to drusen, do not hyperfluoresce during the study; they may appear or disappear, but do not increase in size.

Pathomorphological examination reveals areas of pigment epithelium atrophy and accumulation of fuscin granules in the cells of the retinal pigment epithelium.

The clinical picture of fundus albipunctatus resembles dominant drusen. The ophthalmoscopic picture in these diseases is characterized by similar changes; white-yellow dots are located in the deep layers of the retina, spreading from the posterior pole, where the greatest density is noted, to the periphery, but the distribution and localization of these foci are different. Drusen can be detected in early childhood, but because they are asymptomatic, they are rarely diagnosed in children. FA reveals widespread areas of hyperfluorescence caused by both drusen and atrophy of the retinal pigment epithelium. The pathological gene for drusen exhibits different expression, therefore, patients from the same family have a different picture of the fundus - from single or multiple drusen to atrophy of the pigment epithelium. ERG with drusen is normal, EOG may be changed in late stages of the disease. Fundus albipunotatus may be associated with Alport syndrome.

Alport syndrome Alport syndrome was first presented as a classic phenotype of retinal dystrophy with an autosomal dominant pattern of inheritance, characterized by a primary defect in the basement collagen membrane, which is combined with hereditary nephropathy and deafness. Alport syndrome appears in childhood.

Progressive nephropathy progresses to renal failure in the fourth decade of life, at which time sensorineural hearing loss is noted. The ophthalmoscopic picture is characterized by multiple pale yellow spots located at the level of the pigment epithelium (flecked retina), pigment granules in the macular area and on the periphery, retinal detachment is possible, the optic nerve is not changed, the vessels are within normal limits, the cornea with arcus juvenilis. In the lens there is anterior and posterior lenticonus, subcapsular cataract, spherophakia.

The results of fluorescein angiography indicate hyperfluorescence of fenestrated pigment epithelial defects. Visual field is within normal limits, ERG and EOG are pathological or within normal limits. ERG and EOG are pathological or within normal limits.

Alport syndrome has an autosomal dominant mode of inheritance, although an X-linked form of inheritance has also been described. Since the disease is accompanied by renal pathology, detection of hematuria, proteinuria and renal biopsy can help in the differential diagnosis.

Kandori's spotted retina. In 1959, F. Kandory described a disease that he called “spotted retina with congenital non-progressive night blindness”: dirty yellow spots with clear contours, irregular shapes and different sizes - from the diameter of small retinal vessels to 1.5 DC, located on level of the pigment epithelium and mainly in the equator region, primarily on the nasal side. FA makes it possible to detect hyperfluorescence in the arterial phase, corresponding to the localization of the spots. Migration and accumulation of pigment are not typical for this disease. The macula, retinal vessels and optic nerve head are unchanged. The disease is characterized by mild to moderate decrease in night vision. Central and color vision and visual field were within normal limits. ERG is minus-negative when using high-intensity light stimuli in both scotopic and photopic conditions; its changes indicate functional disorders in the proximal retina. Photopic ERG is normal, scotopic ERG is reduced, but acquires normal amplitude after prolonged dark adaptation. EOG is not changed. Dark adaptation thresholds reach the norm when the dark adaptation period lengthens. In this form of CSNB, the kinetics of visual pigments is disrupted. In terms of functional symptoms, the spotted retina of Kandori is very close to the fundus albuginea, and therefore some authors consider it as a variant of this non-zoological form.

Myopia

16. Hemophilia and blood groups

Bright red, red and brown eyes

18. Corn seeds 302,8320,8306,300….

Corn has a rust resistance gene and a gene for narrow leaves

20. Rabbits. spotted and angora. 26,143,157,24…

Tomato. type of inflorescence and fruit.25 mg

Drosophila has a gene for the color of eyes and bristles.4 mg

Tomatoes have a tall house above the dwarf one. 20 mg

24. the wife has 1 family, and the husband has 4, the son is color blind, group 3 25. Tortoiseshell cats

For Rh factor

27. Yellow pumpkin with white...51..17..

Rabbit ears ram

The smooth shape of the corn seeds dominates the wrinkle. 4152,149,152

Thalassamia

Drosophila in the x chromosome local. Gene determining brush type and body color

Oats have grain color...

The shape of the pumpkin fruit can be spheres or disks. Ext.

Sickle cell anemia. The likelihood is that it will be in a mild form and 4 g cr.

36. The proband has a white curl in his hair above his forehead (autosomal dominant) 75%

37. Proband – female norm. Has five sisters. 6 fingers. Autosomal dominant 0%

Cataract X – linked recessive

39. Night blindness. Out.home. 50%

Duchenne muscular dystrophy. x-clutch

Trisomy group D

41. In most cases, Patau syndrome is not inherited, but occurs as a random event during the formation of germ cells ( eggs And spermatozoa). An error in cell division called non-divergence , can lead to the appearance of reproductive cells with an abnormal number of chromosomes. For example, an egg or sperm may receive an extra copy of a chromosome. If one of these atypical germ cells is involved in the child's genetic makeup, the child will have an extra 13th chromosome in each of the body's cells. Patau syndrome mosaicism is also not inherited, but occurs as a random disorder during cell division at the beginning of fetal development.
Patau syndrome may be inherited due to translocation. A healthy person can carry altered genetic material between chromosome 13 and other chromosomes. This restructuring is called balanced translocation , since no additional material was obtained from chromosome 13. People who are carriers of this type are at increased risk of having children with this disease, although they do not have signs of Patau syndrome.

Trisomy X

A condition in which a girl has three X chromosomes is called trisomy X syndrome. On average, it occurs in one in a thousand apparently healthy girls in the first year of life. Girls with three X chromosomes tend to have lower intelligence than their brothers and sisters with normal chromosomes. Sometimes the syndrome causes infertility, although some women with trisomy X syndrome can give birth to children who have a normal chromosomal complement and are physically healthy. Pathological processes leading to trisomy X occur at the stage of formation of germ cells or at the earliest stages of embryogenesis. Frequency of occurrence of trisomy X – 1 in 1200 girls.

Monosomy X

Monosomy for any of the autosomes usually leads to intrauterine fetal death. Monosomy is the most common type of chromosomal abnormality in spontaneous abortions. Monosomy is the presence of only one of a pair of homologous chromosomes. An example of monosomy in humans is Turner syndrome, which is characterized by the presence of only one sex (X) chromosome. The genotype of such a person is X0, gender is female. Such women lack the usual secondary sexual characteristics and are characterized by short stature and close nipples. The occurrence among the population of Western Europe is 0.03%. In the case of an extensive deletion in any chromosome, partial monosomy is sometimes referred to, for example, cry-the-cat syndrome.

Polysomy by gender

· polysomy on the X chromosome - includes trisomy (karyotes 47, XXX), tetrasomy (48, XXXX), pentasomy (49, XXXXX), there is a slight decrease in intelligence

· polysomy on the Y chromosome - like polysomy on the X chromosome, includes trisomy (karyotes 47, XYY), tetrasomy (48, XYYY), pentasomy (49, XYYYY), clinical manifestations are also similar to polysomy of the X chromosome;

· Klinefelter syndrome - polysomy on the X- and Y-chromosomes in boys (47, XXY; 48, XXYY, etc.), signs: eunuchoid type of build, gynecomastia, weak hair growth on the face, in the armpits and on the pubis, sexual infantilism , infertility; mental development is lagging behind, but sometimes intelligence is normal.

Mosaicism

Trisomy is usually caused by non-disjunction of chromosomes during the formation of the parent's sex cells (gametes), in which case all cells of the child's body will carry the anomaly. With mosaicism, nondisjunction occurs in the embryonic cell in the early stages of its development, as a result of which the karyotype disturbance affects only some tissues and organs. This variant of the development of Down syndrome is called “mosaic Down syndrome” (46, XX/47, XX, 21). This form of the syndrome is, as a rule, milder (depending on the extent of the altered tissues and their location in the body), but is more difficult for prenatal diagnosis.

This type of syndrome appears in 1-2% of cases.

Dasha is developmentally delayed.

Shereshevsky-Turner syndrome is a chromosomal disease accompanied by characteristic anomalies of physical development, short stature and sexual infantilism. Monosomy on the X chromosome (XO).

The appearance of patients is quite unique (although not always). In newborns and infants, characteristic symptoms are observed: a short neck with excess skin and wing-shaped folds, lymphatic edema of the feet, legs, hands and forearms. At school and especially in adolescence, growth retardation and development of secondary sexual characteristics are detected. Adults are characterized by skeletal disorders, craniofacial dysmorphia, valgus deviation of the knee and elbow joints, shortening of the metacarpal and metatarsal bones, osteoporosis, barrel chest, low hair growth on the neck, antimongoloid incision of the palpebral fissures, ptosis, epicanthus, retrogenia, low position of the ears shells The height of adult patients is 20-30 cm below average.

DNA molecule mass

Education norms. egg if nondisjunction in meiosis. If nondisjunction occurred in the second meiosis of oogenesis

(white hrs - we parted ways correctly)

55. disturbances in XYU (black is the Y chromosome.. Striped-) + formation phase

Y-linked inheritance

Autosomal dominant inheritance.

Atosomal recessive inheritance.

X-linked recessive

X-linked dominant

Spermatogenesis scheme

Oogenesis scheme

67. Director of one of the zoos 10 years ago... Visceral leishmaniasis. Leishmania donovani

(leptomonasal form çthrough a bite => leishmanial form)

68.A patient consulted a doctor... Diphyllobothriasis. Diphyllobothrium latum. (industrial households - predatory freshwater fish and crustaceans) smear of feces: eggs and mature segments

70. Semyon Semenych was invited by friends to visit... Belarus... Boar. Trichinosis. Trichinella spiralis. Predatory and omnivorous animals - intermediate households. through poorly cooked meat encapsulated. Larva. Diagnosis: muscle biopsy for larvae, serological reaction

71. Semyon Semyonich and his friends went on a picnic... Fascioliasis. Fasciola hepatica. Adolescaria got on the fruit

72. At a doctor’s appointment, a woman complained... suspicion of enterobiasis (itching) enterobius vermicularis. You need to take a scraping from the perianal folds (eggs). Or Giardiasis (mucus in stool)Lamblia intestinalis

73. A man turned to a neurologist... Echinococcosis Human - intermediate household. Asymptomatic for a long time. Echinococcus granulosus. Serological tests, ultrasound

74. In one of the southern cities... found larvae in sputum, eggs in feces. Barefoot on damp ground. Hookworm/Ancylostoma duodenale.

75. Semyon Semyonich from Finland... Diphyllobothriasis. Diphyllobothrium latum. (industrial households - predatory freshwater fish and crustaceans) smear of feces: eggs and mature segments. Through the calf

76. Semyon Semyonich went on a business trip to Siberia... opisthorchiasis Opisthorchis felineus. Poorly processed thermally. Eggs in feces. Eggs and marita in duodenum.

77. Ancylostomaduodenale (crooked head of the duodenum). Bottom is men's, top is women's
Pathological action: larvae: metabolic products poison the body and cause allergies; larvae in the process of migration injure the skin, blood vessels, lungs, and cause pneumonia.
Sexually mature individuals: toxic-allergic effect; destroys the intestinal mucosa, causes the formation of ulcers, feeds on blood.
Symptoms: inflamed lesions on the skin, rash, eczema. Hemorrhages and pneumonic lesions in the lungs. Violation of kinetic function. Anemia, disturbance of heart rhythm and pressure, perversion of taste.
Detection of eggs in feces, serological reactions, larvae in sputum.

78. Human roundworm (Ascarislumbricoides) 1 - lips; 2 - nerve ring; 3 - pharynx; 4 - phagocytic cells; 5 - "esophagus"; 6 - midgut; 7 - lateral ridge of hypodermis with excretory canal; 8 - oviduct; 9-ovary; 11 – vagina

Disease: ascariasis (2 stages – migratory and intestinal)

Geographical distribution: widespread

Epidemiological characteristics: anthroponosis

Life cycle: mature egg-larva-mature individual---egg---mature egg.

79. Broad tapeworm Diphillobothriumlatum, A- strobilus, b-scolex, 1-bothria, c-ripe joints, 2-rosette-shaped uterus

80. Leishmaniatropica Development cycle: When a mosquito bites, the flagellated forms enter the skin cells, where the flagellum is lost. Leishmania reproduces by longitudinal division, their number in one cell can reach 100 or more. The cell is destroyed, and Leishmania infects neighboring cells. Ulcers appear. The natural reservoir is rodents.

81. Echinococcus tapeworm, Exinococcus granulosus/

1-mature proglottid with eggs, 7-mature eggs in the uterus, 2-hermaphrodite proglottid, 3-immature proglottid, 4-head, 6-suckers, 5-proboscis

82. Entamoeba hystolytica

The color blindness gene and the night blindness gene are inherited linked to the X chromosome.34mogranids.

13. A person has curly hair with an autosomal dominant gene ... + for blood type

Myopia

15. Complementary interaction of non-allelic genes. sickle cell anemia + blood groups

16. Hemophilia and blood groups

20-11-2013, 03:18

Description

First type CSNB (Riggs type, Nougare type) CSNB Riggs type is inherited in an autosomal recessive sex-linked manner. Visual acuity may be slightly reduced, but in most cases it is normal. The field of view under photopic conditions is not changed. The fundus is normal. This type of CSNB is characterized by the absence or significant decrease in the amplitude of the scotopic ERG and the maximum ERG to a standard flash after dark adaptation, while both the a-wave and b-wave are reduced, reflecting the functions of photoreceptors and bipolars, respectively. Photopic ERG latency is approaching normal. The dark adaptation curve is monophasic with the absence of the cone-rod “heregib”, which is due to a significant decrease in the function of the rod system. In CSNB type Nougare with an autosomal dominant type of inheritance, a defect in the β-subunit of rod transducin (C1y38Acr) was noted. At the same time, significantly reduced rod components and slightly reduced cone components are recorded in the subnormal ERG, although some studies have noted the absence of rod function with normal cone function.

In Nuclear CSNB, the sensitivity of rod photoreceptor cells in the dark is reduced, which is due to a phototransduction defect associated with impaired enzyme function, which leads to a decrease in the amplitude of the ERG a and b waves under scotopic conditions, while during light adaptation the retina functions normally. The preservation of the function of the cone system is indicated by normal cone and rhythmic (30 Hz) ERG with normal visual acuity. However, cone and rhythmic ERG may be decreased. With this form of CSNB, the concentration of rhodopsin, its spectral characteristics and recovery kinetics, according to reflectometry, are normal.

It is assumed that in the first type of CSNB, the dysfunction of the rod system is explained by the pathology of phototransduction at one or more of its stages in the outer segments of the rod photoreceptors.

Second type CSNB (Schubert - Bornschein type) . The fundus is not changed, but a mild metallic reflex is possible in the middle part of the fundus and in the periphery.

Type CSNB Schubert - Bornschein characterized by the absence or significant decrease in the COLLAR and rod components of the L-wave of the maximum ERG. The absence or decrease of the b-wave leads to an increase in the amplitude of the a-wave compared to the norm, in this case a minus-negative ERG is recorded. In patients with CSNB combined with myopia, the a-wave is reduced, but not as significantly as the b-wave.

The content and density of visual pigment of rods in situ in patients with CSNB of the Schubert-Bornschein type are normal, which correlates with a normal ERG a-wave. The kinetics of rod photopigment regeneration is also within normal limits, which indicates that the photoreceptors are intact and the presence of a primary defect not in their outer segments, but in the transmission of the visual signal. Judging by the unchanged a-wave and subnormal b-wave, the pathological link in CSNB of the Schubert-Bornschein type is located in the proximal photoreceptors. The similarity of the negative ERG and ERG to a long-term stimulus with the ERG obtained in a live experimental model (in a macaque) with blocking of synapses of depolarizing bipolars with 2-amino-4-phosphonobutyrate (APB) suggests a violation of synaptic transmission from rod photoreceptors to rod bipolars and damage at the level of bipolar synapses of both the cone system (on-channels) and the rod system, consisting exclusively of on-channels. Changes in the functions of the cone system are indicated by the presence of subnormal photopic ERG, with reduced visual acuity.

Analysis of the genetic tree of patients and the identification of various functional disorders in them allowed Y. Miyake (1986) to identify two subtypes of CSNB of the Schubert-Bornschein type: complete - with the absence of the function of the rod system and incomplete - with the presence of its residual function. Both subtypes are characterized by a slight decrease in the function of the cone system.

Full type inheritance form CSNB - X-linked, in most cases the disease is combined with moderate and high myopia, often with nystagmus and amblyopia. This type of CSNB is characterized by the absence of themes of new adaptation and scotopic ERG. Visual acuity is reduced ( 0,8-0,1 ). Boundaries of the field of view during quantitative perimetry for objects V- 4 And 1-4 normal, but narrowed to object I. In the maximum ERG, a slightly reduced a-wave and a largely reduced b-wave are observed. When using a long-term stimulus, a CSNB pattern is revealed in the ERG with preservation of the off-components of the cone system and the absence of op-components. The amplitude of the cone ERG and rhythmic (30 Hz) ERG was significantly reduced after 30 min of dark adaptation and increases again with light adaptation. The kinetics of rhodopsin reduction and its amount are normal.

In CSNB with full gene penetrance, the absolute psychophysical threshold is determined primarily by the cone system. While the rod ERG to a weak short-wave (blue) stimulus is absent, the cone ERG is slightly reduced, i.e. Barrel photopic ERG is intact or subnormal. The cone-rod response is a negative ERG with a preserved a-wave and a significantly reduced b-wave, which is smaller in amplitude than the a-wave. With this type of CSNB, reduced oscillatory potentials are recorded. The EOG light rise is normal.

With incomplete Schubert-Bornschein type CSNB residual function of the rod system is observed. This type is also characterized by an X-linked recessive type of inheritance. Dark adaptation differs from the norm by increasing thresholds by 1,0-1,5 log.el., the absolute threshold is higher than normal, rods participate in its formation. The scotopic ERG is recorded, its amplitude is reduced, the weak blue stimulus rod component, although reduced, can be measured, while the cone ERG is significantly subnormal. In this type of CSNB, the rod system is less affected, oscillatory potentials are recorded more often, and the function of the cone system is reduced to a greater extent than in CSNB with complete gene penetrance. The ratio of the b-wave amplitude to the a-wave amplitude is greater than with the full Schubert-Bornschein CSNB type. With incomplete non-strangeness of the gene after 30 minutes of dark adaptation, flicker amplitude ( 30 Hz) ERG is increased, under conditions of light adaptation the waveform is changed. The main defect is proposed to be at the level of synaptic transmission between photoreceptors and depolarizing bipolars, which determines the pathological response of the rod and cone systems in the ERG.

Histological studies of the retina in both forms of CSNB did not reveal its structural changes.

Carriers of a pathological gene. Identification of carriers of the pathological CSNB gene is important not only for studying the phenotypic manifestations of rhodopsin gene mutations, but also for genetic consultations. Electroretinography is a fairly sensitive method for identifying the initial functional symptoms of hereditary pathology and the intermediate state between normal and pathology, which can be detected in patients without gene expression.

Not every type of CSNB inheritance can be identified as carrier of the gene. The disease, linked to the X chromosome, manifests itself in males and is transmitted through the maternal line. If there is a hereditary history in the family, a decrease in any visual function in a woman is confirmation of the carriage of a pathological gene. However, normal results of functional studies indicate either that the woman has inherited an X chromosome with a normal gene, or that she has inactivated a pathological X chromosome.

Congenital stationary night blindness with changes is glagiogonous. Ogushi's disease. In 1907, S. Oguchi discovered an unusual form of CSNB, in which decreased vision at night was detected already in early childhood. The fundus of the eye in this form of the disease has a gray-white color (decoration) with a metallic sheen, the vessels protrude in relief against a gray background, and the macular area looks dark compared to the surrounding tissues (Fig. 6.5).

The disease is characterized by yellowish phosphorescence of the fundus, similar to decoloration, most often on the periphery of the retina. In most cases, the fundus becomes normal after the patient remains in the dark for several hours. After exposure to photopic conditions, a metallic sheen gradually reappears in the retina. This phenomenon, discovered back in 1913 by Mizuo, is called the Mitsuo-Nakamura phenomenon.

Kinetics of rhodopsin, including both concentration and regeneration, is normal. During long-term dark adaptation, most patients with Ogushi disease experience an increase in the dark adaptation threshold with normal or slightly reduced ERG. The latency (imlicit time) of the rod and cone b-waves of the ERG is normal, but when the retina is stimulated with red light, the latency of the rod b-wave is prolonged.

In Ogushi disease, mutations have been identified in the gene encoding arrestin (retinal S-antigen) and rhodopsin kinase. The nature of the disturbance in background sensitivity in the Mitsuo-Nakamura phenomenon is unknown, but it is assumed that the normal processes of dark adaptation are combined in these patients with the pathological function of post-receptor cellular elements responsible for the generation of the ERG b-wave, which is confirmed by a decrease in the a-wave at high intensity of stimulating light .

There are two types of Ogushi's disease depending on the achievement of the thresholds of the dark adaptation curve: the first - in the presence of the Mitsuo-Nakamura phenomenon, the thresholds of the dark adaptation curve are reached; the second - the thresholds of the dark adaptation curve do not decrease regardless of its duration: the Mitsuo-Nakamura phenomenon occurs, the Mitsuo-Nakamura phenomenon is absent.

The function of the rod system is reduced: The scotopic ERG is subnormal when averaging signals during dark adaptation, although the first response to a bright flash under scotopic conditions is of normal amplitude. The maximum ERG is reduced, the photopic ERG is normal. In the ERG to a long-term stimulus, no changes in on- and off-responses were detected.

In Ogushi disease of the first type, which occurs most frequently, the period of time during which the thresholds of the dark adaptation curve are reached is increased (from 2 before 24 h). In the second type, the thresholds do not decrease below the cone thresholds, and the dark adaptation curve is monophasic. The results of dark adaptation do not depend on the presence of the Mitsuo-Nakamura phenomenon: it can be observed in forms with both monophasic and biphasic curves.

Due to the unusual color of the fundus and the presence of a pathological dark adaptation curve, many authors assumed that the cause of functional pathology was an abnormality in the kinetics of rhodopsin due to a slowdown in its synthesis. However, clinical studies have shown that the amount, regeneration and absorption spectrum of rhodopsin are normal in this form of stationary night blindness. Visual acuity is normal or slightly reduced EOG is normal. Fluorescein angiography reveals diffuse hyperfluorescence of the light-adapted retina.

Ogushi's disease should be differentiated from congenital stationary night blindness with a normal fundus. The characteristic ophthalmoscopic picture with a metallic luster of the fundus is the main criterion that allows a diagnosis of Ogushi's disease to be made with the symptom of night blindness.

Fundus albipunctatus (fundus albipunctatus) N. Lauber in 1910 identified fundus albipunctatus as an independent disease with an autosomal recessive mode of inheritance and differentiated it from albipuncata retinitis, similar in its ophthalmoscopic picture (retimts punclata albescens), which is one of the forms of progressive retinitis pigmentosa. the fundus is characterized by non-progressive stationary night blindness with a typical fundus picture for this pathology, represented by multiple discrete white dots of the same size of irregular shape, which sometimes have a comet configuration, but are so small that they are sometimes difficult to distinguish with indirect ophthalmoscopy. These points are located at the level of the pigment epithelium along the middle periphery of the retina and paramacularly and do not affect the foveal and parafoveal areas (Fig. 6.6)

They have no connection with retinal pigmentation or atrophy of the pigment epithelium. The optic nerve head and vessels are not changed, there is no accumulation of pigment clumps on the periphery. The time to reach the threshold of rod and cone dark adaptation is increased and for rods is 45 min. In some patients, complete dark adaptation cannot be achieved and thresholds always remain elevated at 3-4 log. ate, as in generalized retinal degeneration.

The amplitude of the scotopic ERG is variable: from normal to subnormal and minus-negative. ERG and EOG reach normal values ​​during dark adaptation, but over a longer period of time than normal, which corresponds to a slowdown in the regeneration of visual pigment and the process of reaching the psychophysical threshold of dark adaptation. The cause of these disorders is considered to be the presence of defects in the regeneration cycle of visual pigments, both cone and rod. With this form of CSNB, a significant slowdown in the regeneration of visual (rod and cone) pigments was revealed: the regeneration time of rhodopsin is on average 60 minutes (normally 3 minutes), the regeneration of cone pigments is 20 minutes (normally 75 s). At the same time, in patients with fundus albipunctatus, a normal level of vitamin A in the blood serum is detected and there is no systemic deficiency.

Patients with fundus albipunctatus have mutations in the gene encoding 11-cis-retinollehydrogenase. This microsomal enzyme is found in large quantities in the retinal pigment epithelium, where it serves as a catalyst for oxidative reactions converting 11-cis-retinol to 11-cis-retinal. A decrease in the activity of this enzyme is manifested in slower regeneration of visual pigment.

Fluorescein angiography
(FA) allows you to identify spots of hyperfluorescence that are not associated with the distribution of changes visible ophthalmoscopically; multiple small fenestrated pigment epithelial defects (white spots) in the midperiphery, in contrast to drusen, do not hyperfluoresce during the study; they may appear or disappear, but do not increase in size.

Pathomorphological examination reveals areas of pigment epithelium atrophy and accumulation of fuscin granules in the cells of the retinal pigment epithelium.

The clinical picture of fundus albipunctatus resembles dominant drusen. The ophthalmoscopic picture in these diseases is characterized by similar changes; white-yellow dots are located in the deep layers of the retina, spreading from the posterior pole, where the greatest density is noted, to the periphery, but the distribution and localization of these foci are different. Drusen can be detected in early childhood, but because they are asymptomatic, they are rarely diagnosed in children. FA reveals widespread areas of hyperfluorescence caused by both drusen and atrophy of the retinal pigment epithelium. The pathological gene for drusen exhibits different expression, therefore, patients from the same family have a different picture of the fundus - from single or multiple drusen to atrophy of the pigment epithelium. ERG with drusen is normal, EOG may be changed in late stages of the disease. Fundus albipunotatus may be associated with Alport syndrome.

Alport syndrome Alport syndrome was first presented as a classic phenotype of retinal dystrophy with an autosomal dominant pattern of inheritance, characterized by a primary defect in the basement collagen membrane, which is combined with hereditary nephropathy and deafness. Alport syndrome appears in childhood.

Progressive nephropathy progresses to renal failure in the fourth decade of life, at which time sensorineural hearing loss is noted. The ophthalmoscopic picture is characterized by multiple pale yellow spots located at the level of the pigment epithelium (flecked retina), pigment granules in the macular area and on the periphery, retinal detachment is possible, the optic nerve is not changed, the vessels are within normal limits, the cornea with arcus juvenilis. In the lens there is anterior and posterior lenticonus, subcapsular cataract, spherophakia.

The results of fluorescein angiography indicate hyperfluorescence of fenestrated pigment epithelial defects. Visual field is within normal limits, ERG and EOG are pathological or within normal limits. ERG and EOG are pathological or within normal limits.

Alport syndrome has an autosomal dominant mode of inheritance, although an X-linked form of inheritance has also been described. Since the disease is accompanied by renal pathology, detection of hematuria, proteinuria and renal biopsy can help in the differential diagnosis.

Kandori's spotted retina. In 1959, F. Kandory described a disease that he called “spotted retina with congenital non-progressive night blindness”: dirty yellow spots with clear contours, irregular shapes and different sizes - from the diameter of small retinal vessels to 1.5 DC, located on level of the pigment epithelium and mainly in the equator region, primarily on the nasal side. FA makes it possible to detect hyperfluorescence in the arterial phase, corresponding to the localization of the spots. Migration and accumulation of pigment are not typical for this disease. The macula, retinal vessels and optic nerve head are unchanged. The disease is characterized by mild to moderate decrease in night vision. Central and color vision and visual field were within normal limits. ERG is minus-negative when using high-intensity light stimuli in both scotopic and photopic conditions; its changes indicate functional disorders in the proximal retina. Photopic ERG is normal, scotopic ERG is reduced, but acquires normal amplitude after prolonged dark adaptation. EOG is not changed. Dark adaptation thresholds reach the norm when the dark adaptation period lengthens. In this form of CSNB, the kinetics of visual pigments is disrupted. In terms of functional symptoms, the spotted retina of Kandori is very close to the fundus albuginea, and therefore some authors consider it as a variant of this non-zoological form.

Problem 109.
Rosa and Alla are sisters and both, like their parents, suffer from night blindness. They also have a sister Elsa with normal vision, as well as a brother Abgryz and a sister Izya, who also suffer from night blindness. Explain the birth of Elsa's sister with normal vision if both parents are sick?
Solution:
The fact that parents suffer from night blindness, out of five (100%) children born, one child (25%) is healthy indicates that this trait is inherited as an autosomal dominant trait.


AA - homozygote - night blindness;
aa - homozygote - normal vision;
Aa - heterozygote - night blindness.

Let us determine the possible genotypes of the offspring if both parents are heterozygotes

Crossing scheme

R: Aa x Aa
G: A, a, a, a
F 1: 1AA:2Aa:1aa
Three types of genotype are observed. Genotype split: 1:2:1.
Phenotypes:
AA - night blindness - 25%;
Aa - night blindness - 50%;
aa - normal vision - 25%.
Three types of phenotype are observed. Phenotype split: 3:1.

When heterozygotes (Aa) are crossed with each other, the probability of producing a child with normal vision is 25%. This is possible when this disease is inherited according to the type of autosomal dominant inheritance of the trait.

Oguchi disease is a congenital night blindness transmitted by an autosomal recessive, X-linked inheritance pattern.

Problem 110.
Oguchi disease, also called congenital night blindness, is an autosomal X-linked recessive form of congenital night blindness associated with discoloration of the fundus and abnormally slow adaptation to darkness. How can we explain the fact that three healthy girls and two boys were born to healthy parents, one of the two boys suffers from Oguchi disease - a disease of night blindness? Determine the genotypes of the parents and the newborn boy,
Solution:
Ho - allele of the Oguchi gene;

XOXO - homozygote - normal vision;
XoXo - homozygous - Oguchi disease;
XOXO - heterozygote - normal vision;
XOU - normal vision;
HoU - Oguchi's disease.
Considering that this disease is an autosomal recessive X-linked form of congenital night blindness and that three healthy girls and two boys were born to healthy parents, one of whom suffers from Oguchi disease, it can be assumed that the mother is a carrier of this disease. disease and its genotype has the form - XOXO, the genotype of a healthy father will have the form: XOU. The genotype of the sick boy will be XO.

Crossing scheme

R: XOXO x XOU
G: XO, XO XO, U
F 1: XOXO:XOXO:XOU:XO
Four types of genotype are observed. Genotype split: 1:1:1:1.
Phenotypes:
XOXO - normal vision - 25%;
XOXO - normal vision - 25%;
XOU - normal vision - 25%;
HoU - Oguchi disease - 25%.
Two types of phenotype are observed. Phenotype split: 3:1.

Thus, with this crossing, offspring appear in which all girls are born healthy, but half of them are carriers of the gene Oguchi disease, and among boys, half are healthy and half are suffering Oguchi disease.

Problem 111.
A woman suffering from Oguchi disease, a congenital form of night blindness, which is transmitted by an autosomal recessive, X-linked type of inheritance, married a man also suffering from a congenital form of night blindness, called nyctalopia, transmitted by an autosomal dominant type of inheritance. Their marriage produced three boys, all of whom suffered from both forms of night blindness (Oguchi disease and nyctalopia). What are the genotypes of women and men? Why do all boys inherit both types of hereditary night blindness? Determine the possible genotypes and phenotypes of the children from their marriage. What is the likelihood of having girls with both vision anomalies?
Solution:
Ho - allele of the Oguchi gene;
XO - allele of the gene for normal vision;
A - allele of the night blindness gene;
a - allele of the gene for normal vision;
Since a woman suffers from Oguchi disease, but does not have nyctalopia, her genotype is: aaHoHo. If a man suffers nyctalopia and he is missing Oguchi disease and all born boys inherited both traits from their parents, then he is homozygous for both traits, his genotype is AAHOU.

crossing scheme

R: aaHoHo x AAHOU
G: aHo AHO, AU
F 1: 1АаХОХо: 1АаХОУ
Two types of genotype are observed. Genotype splitting: (1:1).
Phenotypes:
AaХОХо - nyctalopia, absence of Oguchi disease - 50%;
AaHoU - nyctalopia, Oguchi disease.
Two types of phenotype are observed. Phenotype splitting: 1:1.

Thus, the probability of having boys born with both forms of night blindness is 100%; all girls born will suffer nyctalopia and are carriers of the gene Oguchi disease.