Albinism – group of the hereditary pathologies which are characterized by violations or total absence of pigmentation of skin, a hair, an eye iris of the eye. The main symptoms of a disease is very light skin and hair, blue or reddish color of eyes, in some cases there can be sight violations. Diagnosis of albinism is made on the basis of the present status of the patient, and also genetic researches. There is no specific treatment of albinism today, use palliative therapy (sight correction), and also there is a number of recommendations the patient how to behave in the sun, to protect skin and to reduce probability of complications.
Albinism – set of genetic pathologies at which processes of formation or accumulation of a pigment of melanin in cells of skin, its appendages, an iris of the eye and a retina of an eye are broken. This state is known from ancient vremenen, strikes persons of any nationality or race. However the frequency of occurrence of albinism differs at different nationalities – it makes from 1:10000 to 1:2000000. Also this indicator is not identical to different forms of a disease which are classified by genetic signs in recent years. Earlier allocated only two forms of albinism (eye and skin and eye) though the modern genetics distinguishes, at least, seven various types of pathology. Besides, there is a number of hereditary diseases which simptomokompleks, in addition, includes also albinism – for example, a syndrome of Chediaka-Higasi, Germansky-Pudlaka's disease.
The main reason for development of albinism – violation of metabolism of amino acid of a tirozin, and, as a result, the full block or weakening of synthesis and adjournment of a pigment of melanin. Can lead various mutations of genes which directly or indirectly participate in process of formation of melanin to this state. For example, the most severe form of albinism – glazokozhny 1A – is caused by a difficult mutation of a gene of alb-OCA1 located on the 11th chromosome. It codes the sequence of enzyme tyrosineelements, and at nonsense-mutations its production in an organism completely stops. As a result formation of melanin also completely stops, as becomes the reason of heavy glazokozhny albinism. This state on the autosomno-recessive mechanism is inherited.
Other type of this disease – glazokozhny albinism 1B - is caused by violation of the same gene of alb-OCA1, however at the same time its functioning continues. More than 50 mutations of the above-stated gene are associated with this pathology, each of which in a different measure influences activity tyrosineelements. Therefore expressiveness of symptoms at glazokozhny albinism 1B is also very variable – from almost total absence of melanin in fabrics to slightly lighter shade of skin and hair. In some cases patients with such form of pathology are capable to sunbathe, at them hair darken with age, a pigmentary nevus can appear. An interesting subtype of this disease is temperature and sensitive albinism at which activity tyrosineelements sharply falls at a temperature over 37 degrees. It leads to the fact that pigmentation is stronger to be shown on colder parts of the body – brushes, feet. Whereas the head, eyes, axillary hollows often are left practically without pigment.
Glazokozhny albinism of type 2 is the most widespread kind of this pathology. However at the same time genetic disorders do not affect synthesis tyrosineelements which remains at the sufficient level, activity and structure of enzyme also do not suffer. Albinism of this kind is caused by a mutation of the gene located on the 15th chromosome. Presumably, it codes a protein (R-protein) of a membrane melanosy which is responsible for transport of a tirozin. At this form of albinism of manifestation of deficiency of melanin are also very variable, besides, pigmentation can amplify over time. The reasons of such phenomenon are still not found out. Glazokozhny albinism of type 2 on autosomno-recessive type is inherited.
Other form of a disease, glazokozhny albinism of type 3 occurs almost only at negroid race. At it genetic researches revealed mutations of a gene of TRP-1 located on the 9th chromosome. The similar gene at mice is responsible for brown coloring of wool, its functions at the person are authentically unknown. It is supposed that it controls formation of black fraction of melanin (eumelanin), and violation of its structure leads to primary synthesis of a brown kind of a pigment. As well as other glazokozhny forms of albinism, type 3 are given on the autosomno-recessive mechanism.
Each type of albinism are characterized not only disappearance of melanin from skin and its appendages, but also the visual device of an eye – an iris of the eye and a pigmentary layer. It leads to violations of a refraction and transparency of a cornea, an astigmatism and squint, a foveolyarny hypoplasia of a retina. The albinism forms (so-called eye types) which are characterized only by damage of organs of vision are had. The most common form of eye albinism is transferred on recessive type and is linked to the H-chromosome. It is caused by a mutation of a gene of GPR143 coding a receptor to G-protein of melanotsit of eyes. As a result of it formation processes melanosy are broken, as becomes the reason of development of eye albinism. In the 1970th year the autosomno-recessive form of this disease was also revealed, however the pathogenesis of this type is still not defined – alb-OCA1 gene mutations, others (36%) – violations in the R-protein gene had a part (14%) of such patients. Almost at a half of patients with autosomno-recessive eye albinism it was not succeeded to establish a genetic cause of illness.
Classification of albinism
Earlier all cases of albinism divided only on phenotypical manifestations – full and incomplete. All types of glazokozhny albinism which are characterized by the expressed violations of pigmentation of eyes, skin and its appendages concerned to the first. Carried eye types of a disease, and also those kinds of pathology which resulted in spottiness of skin to incomplete forms. Now use more often genetic classification within which allocate such types of albinism:
- Glazokozhny albinism type 1A – its reason acts a nonsense-mutation of a gene of alb-OCA1 which simply "switches off" its expression. As a result of it synthesis tyrosineelements in an organism completely stops.
- Glazokozhny albinism type 1B – as well as in the previous case, it is caused by alb-OCA1 gene mutations, however at the same time its expression is possible. Defective enzyme of a tirozinaz with different degree of activity is as a result synthesized. Expressiveness of displays of such albinism depends on gene mutation type.
- Temperature and sensitive glazokozhny albinism – is a 1B version, is characterized by changeable activity tyrosineelements which depends on temperature. Skin manifestations moderate whereas ophthalmologic violations can be considerably expressed. These features of such albinism are caused by more high temperature of eyes – therefore, the tirozinaza in them is less active.
- Glazokozhny albinism type 2 – is caused by a mutation of the gene coding the R-protein which is an element of a membrane intracellular melanosy. As a result transport of a tirozin in a cage is broken, and synthesis of melanin does not happen even at normal activity tyrosineelements.
- Glazokozhny albinism type 3 – is a consequence of mutations of a gene of TRP-1 which, presumably, controls formation of an eumelanin. Occurs only at Africans, causes development of brown coloring of skin and hair and moderate ophthalmologic violations.
- Eye albinism recessive and connected with the H-chromosome. It is caused by a mutation of a gene of GPR143 which is responsible for some elements of intracellular information transfer.
- Autosomno-retsessivny eye albinism – it did not manage to be connected with concrete genetic disorders yet. It is supposed that a part of cases of such disease is eye forms of glazokozhny types of pathology – 1B and 2.
Even within one genotype of albinism significant differences in degree of expressiveness of symptoms are possible. It is connected with the fact that mutations of different type unequally influence production of melanin.
Refer the pallor of integuments especially noticeable at the birth of the sick child to the main displays of albinism. Quite often skin has a pinkish shade because of the translucent blood vessels, an eye at the birth blue, but in some foreshortenings can also have reddish color. Further, in the course of growth, symptoms of albinism can change a little depending on disease type. At type 1A which is the heaviest synthesis of melanin in an organism does not happen in general therefore at the patient white skin color and a hair and blue eyes for life remains. Albinism of type 1B is characterized by bystry accumulation in hair of a yellow pigment therefore they accept light-straw color, often with age there is a pigmentation of eyelashes and a cornea of eyes.
Temperature and sensitive albinism is often shown by a peculiar distribution of melanin – normal pigmentation is observed on extremities whereas head skin remains pale, hair also keep white color. Eyes because of raised, than on extremities, temperatures remain with such patients of blue color. Considerable changeability of symptoms characterizes also albinism of type 2 – from almost total absence of pigmentation to an imperceptible posvetleniye of skin and hair. Also melanin synthesis improvement is often characteristic of such form of a disease with age – hair begin to darken, to appear freckles, to arise suntan. However with stay on a sunlight it is necessary to be careful – skin of patients with albinism is extremely sensitive to ultra-violet radiation, easily there are burns of skin and photodermatitis.
Characteristic symptom of albinism is violation of visual acuity at patients and other ophthalmologic changes. Decrease in sight of subjects vyrazhenny, than more weakly is synthesized in an organism melanin, especially in a cornea and a pigmentary layer of a retina. Besides, frequent satellites of albinism are squint, an astigmatism, which arise at once at the birth or in the first years of life. At eye forms of a disease similar symptoms are shown without violation of pigmentation of skin and hair. Due to the lack of a protective layer of melanotsit patients with albinism often have a photophobia sometimes passing into a day blindness.
Diagnosis of albinism
Definition of albinism in many cases perhaps at once after the patient's birth – the dermatologist, estimating a condition of pigmentation of skin and hair it is capable to reveal a disease and to approximately learn its version. Further observation at this expert is necessary for monitoring of a course of pathology and for prevention of possible complications – for example, skin cancer. The ophthalmologist at albinism quite often reveals transparency of an iris of the eye, at adult patients the retina hypoplasia in the field of a yellow spot often is defined. The Foveolyarny reflex is sharply lowered or is absent. The depigmentation centers often are found in persons with incomplete albinism at an eye bottom. Also other violations of sight – , an astigmatism, a miopiya are found.
For confirmation of the diagnosis and specification like pathology the doctor geneticist can appoint a sekvenirovaniye of the genes associated with it. Also important role is played by drawing up the hereditary anamnesis, genetic diagnostics of relatives of the patient for identification of carriers of defective genes is possible. A rare and expensive method of diagnosis of albinism is definition of tirozinazny activity in fabrics (for example, in hair follicles), but it allows to specify the forecast of a disease several. The better activity of this pigment in fabrics is kept, the expressiveness of other symptoms of this pathology is lower. Differential diagnosis of albinism should be carried out with other hereditary pathologies which are followed by similar skin and ophthalmologic symptoms. First of all it is syndromes of Chediaka-Higasi and Germansky-Pudlaka, the H-linked ichthyosis, a mikroftalmiya, Kallman's disease.
Treatment and forecast of albinism
Specific treatment of albinism does not exist today, only preventive actions allowing to improve quality of life of the patient are developed. Protection of eyes against a sunlight is necessary for preservation of the existing level of sight – it is reached by wearing special sunglasses or contact lenses. Emergence on a bright sun it is necessary to avoid or protect skin special creams and lotions. If to adhere to these recommendations, then in general the forecast of albinism favorable – patients can live long and full-fledged life. At the same time regular consultations of the dermatologist and ophthalmologist – are necessary for prevention of complications, such as cancer of skin or an otsloyka of a retina.