Causes of albinism

Albinism is caused by a lack of the pigment melanin, whichgives hair, skin and eyestheir colour.

Melanin is also involved in the development of the retina (the thin layer of nerve cells that line the inside of the back of the eye) andnerve connections between the retina and the brain, which is why most people with albinism have vision problems.

In people with albinism, the cells that make melanin do not work due toa faulty (mutated) gene.

There are two main types of albinism:

• oculocutaneous albinism (OCA) the most common type that affects the skin, hair and eyes
• ocular albinism (OA) a rarer type that mainly affects the eyes

These two types are caused by differentgenetic faults, and they can be divided into many further sub-types that are caused by a number of different faulty genes.

Howalbinism is inherited

In most cases, including all types of OCA and some types of OA, albinism ispassed on in what is known as an autosomal recessive inheritance pattern.

However, some types of OA are caused by a mutation on the X chromosome (one of the sex chromosomes). This is known as an X-linked inheritance pattern.

Autosomal recessive inheritance

An autosomal recessive condition means you need to inherit two copies of the faulty gene (one from your mother and one from your father) to have the condition.

It is estimated that about one in 70 people carry the faulty gene that causes OCA. Carriers of the gene are not affected by the condition and have a normal amount of melanin.

If both parents carry the gene, there is a one in four chance that their child will have albinism and a one in two chance they will be a carrier.

X-linked inheritance

X-linked recessive conditions often don't affect females because females have two X chromosomes, one of which will be normal and can usually compensate for the mutated chromosome. However, females who inherit the mutation will become carriers.

If a male inherits the mutation from his mother (males receive a Y chromosome from their fathers), he will not have a normal copy of the gene and will develop albinism.

When a mother is a carrier of an X-linked mutation, each daughter they have has a one in two chance of becoming a carrier and each son they have has a one in two chance of having albinism.

When a father has an X-linked condition, his daughters will become carriers of the mutation.

Genetic counselling

If you have a history of albinism in your family, or you have a child with the condition, you may be referred for genetic counselling.

Genetic counselling is a service that provides support, information and advice about genetic conditions.

An adult or child diagnosed with albinism may also be referred for genetic counselling to discuss how the condition was inherited and what the chances are of passing the condition on.