Definition
The term albinism is derived from the Latin word for white, “albus”. It is a collective term for a large number of congenital genetic defects, all of which result in those affected suffering from a lack of pigment, which is mainly noticeable by a light skin and hair colour. Albinism is not only found in humans, but also in the animal kingdom, where those affected are often referred to as albinos.
The origin of albinism
Today, 5 genes are known whose mutation causes albinism, although it cannot be ruled out that there are other genes that could be responsible. A distinction is made between oculocutaneous albinism (OCA) type 1, type 2, type 3, type 4 and ocular albinism (OA). Most of these genetic defects are inherited autosomal recessively, which means that both copies of the gene in a person (i.e. both from the father and the mother) must be defective for the disease to manifest itself.
Consequently, two outwardly healthy parents can give birth to a sick child. In humans, albinism occurs with a frequency of 1:20,000. In certain regions (for example, Africa), the frequency is higher, and the risk of the disease can rise to 1:10,000 or even higher.
Causes of albinism
The pigment deficiency can either be caused by a disturbance in the synthesis of the pigment melanin or by a structural defect in the melanosomes. The pigment melanin is produced in the melanocytes, specialized cells located in the skin. They contain small vesicles, the melanosomes, which contain enzymes necessary for the synthesis of melanin.
The most common cause of albinism is a defect in the enzyme tyrosinase (oculocutaneous albinism type 1). This enables the first step of melanin production in which the amino acid tyrosine is hydroxylated. However, albinism does not always occur as an independent disease.
Often it is also associated with other disease symptoms in the context of a syndrome. Syndromes that are often associated with albinism are the Angelmann and Prader-Willi syndromes, more rarely the Hermansky-Pudlak or Griscelli syndromes. The symptoms of albinism vary quite a lot from individual to individual, as the severity of the disease depends on which component of the synthesis is defective and how large the almost always existing residual activity of the affected component is.
A classic example of albinism is the light, matt-white skin. Consequently, these patients have an increased risk of sunburn and skin cancer. However, the structure of the skin is not changed.
In addition, the body hair is usually very light or really completely white. The iris of the eyes is also lighter than usual due to the lack of melanin. Although they can actually be light blue, light green or even light brown, they often appear reddish, as the reduced pigment makes it possible to see the blood vessels shining through from inside the eye.
In addition to these physical complaints, many albinism sufferers also suffer from their disease, as its strikingly different appearance often leads to discrimination or exclusion. Among fair-skinned people this phenomenon is usually less pronounced, as people with albinism are not as conspicuous, and in the case of incomplete forms it can even remain undiagnosed. However, albinism is highly stigmatising, especially among dark-skinned peoples, and in some peoples there is even a general superstition that people with albinism bring bad luck.
The most common forms of albinism in Europe affect not only the skin but also the eyes. However, the degree of pronounced symptoms varies greatly depending on the genetic defect and the form of albinism. In principle, the pigment deficiency, which can be more or less pronounced in albinism, leads to a brightening of the eye colour.
Mostly the eyes then appear light blue. The shimmering through of small blood vessels can lead to the eyes appearing slightly pink or light red if the lightening is strong. However, this is not directly a red colouring of the iris.
In many cases, however, the pigment deficiency is not so pronounced, so not everyone with albinism has a reddish iris. Furthermore, the eyes of many people with albinism are very sensitive to light (photophobia). Disorders of spatial vision and visual acuity are also possible in people with albinism.
In the rare ocular form of albinism, only the eyes are affected, but the skin remains normally dark. Due to the poor pigmentation of the iris, patients with albinism usually have a generally increased sensitivity to glare. Other aspects of vision may also be affected, as melanin is also involved in the development of some components of the visual complex.
For example, a melanin deficiency has a negative effect on the development of the optic nerves. This can lead to impaired spatial vision, eye tremor (nystagmus) or manifest strabismus (squint). Visual acuity can also be reduced in albinism, as melanin is needed for the complete development of the place of sharpest vision on the retina (fovea centralis).
In patients with albinism, it is either incomplete (hypoplasia) or not developed at all (aplasia). Patients with albinism are often also short-sighted or farsighted, or they can only see contrasts with difficulty. However, colour perception is always unaffected.