Albinism

Albinism is a phenomenon that affects different types of metabolism (plant or animal) and results in the absence of yellow, red, brown or black pigments in the body. More known in vertebrates, this hypopigmentation can result from the complete absence of pigment cells, the absence of the hormonal stimulation required for the synthesis of the pigment or metabolic abnormalities inside the cells.

In humans, albinism is a very rare hereditary and congenital disease. It is due to the absence of melanin, a brown pigment normally present in the skin, hair and eyes. Thus the complete albino has pinkish-white skin, discolored hair, pink iris and red pupils revealing the blood vessels in the back of the eye.

There are different forms of human albinism :

• oculocutaneous albinisms that reach the eye, the skin, the hair.
• ocular albinisms that affect the eye.
• complex albinisms that are accompanied by pathologies that are life-threatening.

Transmission of albinism

The "albinism" character corresponds to a gene different from the ancestral gene, that is to say to a gene that has undergone the mutation process. A mutation is most often linked to errors in DNA replication. They correspond to chromosomal abnormalities. These are gene mutations responsible for hereditary diseases and they are therefore at the origin of the appearance of "albino gene".

The global incidence of albinism, all forms combined, is 1 case for 20,000 births, there are very large disparities depending on the region. Indeed this figure varies according to the populations. The most affected are in Equatorial Africa and South America.

In some parts of Africa (Niger, Aland Island) the frequency is 1/1000. In the United States, it is 1/12000 among African-Americans. The South American zone appears to be one of the most affected: we reach 3.5% in Panama.
In Western Europe, the frequency is 1 in 16000 births, about 20 times less than in Equatorial Africa. Conclusion

Causes

Inbreeding, mainly in Africa, reveals the importance of manners in the distribution of the disease. A crossbreeding is described as inbred when the spouses are more or less closely related. It is easy to show that the practice of inbreeding is accompanied by a phenomenon of increase of the homozygotes: for example, when it is a marriage between first cousins the coefficient would be 1/16, and would reach 1 / 14 in the case of a union between brother and sister.

The metabolism of vitamin D and more particularly its synthesis under the effect of light rays, are related to the more or less important amount of melanin. Thus, in certain latitudes and more particularly in hot countries, an individual whose skin contains a large amount of melanin (black race) is more exposed to rickets than white. Ritis is due in part to a deficiency of vitamin D. This is why these people, because of their metabolism, are particularly affected by albinism.

Conclusion

Albinism in humans is a very rare genetic and congenital anomaly that is passed down from generation to generation. This inherited disease is due to the lack of a brown pigment: melanin and is characterized by a very white skin, white hair or straw blonde, discolored hair and a pink iris.

Albinism remains today a phenomenon whose distribution in the world is unequal and more marked in the countries of African civilization. Indeed, after several statistical studies, scientists have found that this disease is more prevalent in dark skinned people, that is, synthesizing a lot of melanin. However, it has never been proven that the frequency of albinism in a population is proportional to the amount of melanin produced by this same population. Only the African custom of admitting and trivializing consanguineous marriages is at the origin of this unequal distribution. Indeed, two individuals are much more likely to have the same abnormal gene if they have a common ancestor than if they do not have one.

(pictures source)