Albinisme

Qu'est-ce que l'albinisme ?

Albinism is an inherited condition that leads to someone having very light skin, hair, and eyes. It happens because they have less melanin than usual in their body. Melanin gives skin, hair, and eyes their colour.

Except for vision problems, most people with albinism are just as healthy as anyone else.

Signs and symptoms include:

• Pale skin (or paler than expected).

• Hair that is very light blonde, brown, or reddish.

• Eyes that are pink, light blue, green, grey, or light brown. In certain light conditions there is a reddish tint reflected through the iris and pupil from the retina and the eyes appear red (similar to the 'red eye' in flash photography).

• Eyes that are sensitive to light.

• A “lazy eye”.

• Repetitive horizontal movements of the eyes (called nystagmus).

• Vision problems.

While most people with albinism have very light, pale skin and hair, levels of pigmentation can vary depending on the type of albinism.

Oculocutaneous albinism (OCA) involves the eyes, hair and skin. Ocular albinism (OA), which is much less common, involves only the eyes, while skin and hair may appear similar or slightly lighter than that of other family members.

Approximately 1 in 17,000 people in Europe and the USA have one of the types of albinism, although in some parts of the world it is more common than this. In sub-Saharan Africa cultural norms permit marriages between family members. This lack of genetic mixing means the prevalence increases up to 1 in 1000. Albinism can affect all races and also affects other species, such as mice.

La plupart des enfants atteints d'albinisme naissent de parents qui ont une couleur de cheveux et d'yeux normale pour leur origine ethnique.

Albinism is divided into OCA (which is more common and has many forms) and ocular albinism (OA), which is rare.

Oculocutaneous albinism (OCA)

Seven forms of OCA are now recognised - OCA1, OCA2, OCA3, OCA4, OCA5, OCA6 and OCA7. Some are further divided into subtypes:

OCA1

OCA1 results from a genetic defect in an enzyme called tyrosinase. This enzyme helps the body to make melanin pigment. There are two subtypes of OCA1.

In OCA1A, the enzyme is completely inactive and absolutely no melanin is produced, leading to white hair and very light skin.

In OCA1B, the enzyme is minimally active and a small amount of melanin is produced. This leads to hair that may darken to blond, yellow/orange or even light brown, as well as slightly more pigment in the skin.

OCA2

OCA2, results from a genetic defect in a different protein that helps the tyrosinase enzyme to function. People with OCA2 make a tiny amount of melanin pigment and can have hair colour ranging from very light blond to brown.

OCA3

OCA3 is rare and results from a genetic defect in a related protein. People with OCA3 can have normal pigmentation.

OCA4

OCA4 results from a genetic defect in a protein that helps the tyrosinase enzyme to function. It is similar to OCA2.

OCA 5-7

OCA5-7 were recognised in humans in 2012 and 2013. Currently, these types of albinism are considered to be uncommon.

Albinisme oculaire (AO)

OA is much less common and only involves the eyes. The person's skin and hair may appear similar or slightly lighter than that of other family members.

Researchers have also identified several other genes that result in albinism with other features. These include Hermansky-Pudlak syndrome (patients have albinism with bleeding problems and bruising). Other albinism-related syndromes include Chédiak-Higashi syndrome and Griscelli's syndrome.

The genes for occulocutaneous albinism (OCA) are located on 'autosomal' chromosomes. These are the 22 pairs of chromosomes that contain genes for our general body characteristics, compared to the one pair of sex chromosomes.

We normally have two copies of these chromosomes - one inherited from our father, the other inherited from our mother. For a recessive condition (like most types of albinism) to occur, both of the person's chromosomes must carry that trait - that is, the one from the mother and the one from the father.

That means that most types of albinism result from inheriting an albinism gene from both the mother and the father (who often have normal pigmentation themselves, as their OTHER gene is normal). When both parents carry the albinism gene (and neither parent has albinism) there is a one in four chance at each pregnancy that the baby will be born with albinism.

If a parent has albinism then they will pass on one affected gene to their child. The child will still only develop albinism if they also inherit an albinism gene from the other parent.

Diagnosis is based on examination and observation. The only type of albinism with white hair at birth is OCA1.

Hair bulbs plucked from the scalp can be tested to check for the ability to make melanin. This can detect OCA type 1A but does not rule out other types of albinism.

The most accurate test is a genetic test. The test is useful only for families which contain people with albinism and even then, not all cases can be detected.

Based on hair and skin having less pigmentation:

• Hermansky-Pudlak syndrome.

• Chediak-Higashi syndrome.

• Angelman syndrome and Prader-Willi syndrome.

• Vici syndrome.

• Waardenburg syndrome type II.

• Tietz albinism-deafness syndrome.

• Griscelli syndrome.

People with albinism typically experience vision problems, skin problems and social problems.

Vision problems

Eye problems in albinism result from the abnormal development of the eye because of a lack of pigment.

The most common ones include:

• Nystagmus (regular horizontal back and forth movement of the eyes).

• Squint (muscle imbalance of the eyes).

• Sensitivity to bright light or glare.

• Problems with vision and focus.

People with albinism are sensitive to glare as extra light gets into their eyes through the thinner iris. However, they do not prefer to be in the dark, as they need light to see just like anyone else.

They may be either far-sighted or near-sighted and usually have astigmatism. Because the retina (the surface inside the eye that receives light) does not develop normally, the nerve pathways transmitting vision to the brain also don't develop normally.

Problèmes de peau

People with albinism are very susceptible to burning and subsequent cancer de la peau. High-factor sun protection cream and avoidance of sunlight are essential.

In tropical countries, people with albinism may not have access to adequate skin protection and may develop life-threatening skin cancers. They need to use sunscreens rated 20 SPF or higher, together with opaque clothing, in order to enjoy outdoor activities in summer.

Difficultés sociales

Children with albinism can experience difficulty with harcèlement and social relationships because their condition is so visible. They look different from their families, friends and other members of their ethnic group.

In some ethnic groups the difference may be dramatic, especially within communities of colour, where the race or paternity may be questioned. Support of family and friends and contact with other affected people can be helpful.

Vision treatments

Treatment of albinism is mainly with support and help with vision:

Chirurgie

Surgery can be used to correct squint, which may improve the appearance of the eyes. However, surgery cannot improve eyesight or depth (binocular) vision. Eye specialists usually start to treat squint in infants of about 6 months of age. They may recommend a patch over one eye, or the wearing of glasses.

Surgery can also help reduce nystagmus, if severe. Nystagmus may reduce over time. People with albinism may find ways of reducing nystagmus while reading, such as placing a finger by the eye, or tilting the head at an angle where nystagmus is reduced.

Sunglasses

Sunglasses or tinted contact lenses may help with light sensitivity. Indoors, it is important to place lights for close work over a shoulder rather than in front.

Glasses

Some people with albinism use glasses which have small telescopes mounted on, in or behind their regular lenses (bioptics). This enables them to look through either the regular lens or the telescope. Some patients wear contact lenses with a special iris tint.

Various classroom aids help children with albinism

High-contrast written material with large text can help children to read: black on white high-contrast material is the easiest to read. Because children with albinism often have difficulty keeping track of their place on the page if copying text, it may help to allow them to write in the textbook. Audio tapes may be helpful. Computers with large text display will make reading easier.

Giving the child copies of the teacher's notes may be useful; sometimes magnifying devices can also be helpful.

Albinism cannot be prevented, as it is an inherited (genetic) condition rather than an illness.

Gene testing can be used to determine if a baby in the womb has albinism. Amniocentesis is performed at 16 to 18 weeks of gestation in pregnancy. Those considering testing of this sort should be made aware that, whilst children with albinism are usually severely visually impaired, they are otherwise healthy and have a normal lifespan.

Life expectancy is normal for a person with albinism. Although vision is usually severely impaired, intellect and development are normal.

People with albinism have an increased risk of sunburn and of skin cancers as their skin is not protected by pigment.

Dr Mary Lowth est l'auteur ou l'auteur original de ce dépliant.