What is albinism?
Albinism (say: AL-buh-niz-um) is a name used for genetic conditions that cause a person to have no pigment or less pigment than usual. Pigment is what gives our eyes and skin their colour.
There are two types of albinism:
- When the skin, hair, and eyes are involved, it is called oculocutaneous (say: ock-you-lo-kyoo-TAY-nee-us) albinism (OCA).
- When the eyes are involved, but skin and hair colouring are normal, it is called ocular albinism (OA).
Both types of albinism will cause your child to have poor eyesight. Each child’s vision will be affected in a different way. Albinism does not usually cause other medical problems or cause your child to have poor health.
Who albinism affects
- OCA can affect both girls and boys. It is more common than OA.
- OA is a disorder that affects boys. (Please see How the Body Works, X-linked Inheritance)
- OCA is more common that OA.
Albinism and your future children
Albinism is usually passed either from one unaffected parent (OA) to a child or from both unaffected parents (OCA) to a child. A parent who is not affected with albinism but has the gene mutation that causes it is called a “carrier”.
Different types of albinism are passed on in different ways. The explanation of how it is passed depends on the pattern of inheritance. If you have one child with albinism, the chance that you will have another child with albinism is 25%, or 1 in 4.
OCA usually has autosomal recessive inheritance
Most types of OCA have autosomal recessive inheritance. This means that both parents are carriers of an OCA mutation. The chance of any person being a carrier of OCA varies from 1 in 85 in African Americans to 1 in 100 in Caucasians.
People with different characteristics have different chances of having a child with OCA:
- If you and your partner are unaffected carriers of the OCA gene mutation, you have a 1 in 4 chance of having a child with OCA with each pregnancy. This means that 3 out of 4 are unaffected. It is possible to have more than one child with albinism.
- If you are affected with OCA, the risk is very low (0.5%) of having children with OCA if your partner is not affected or a carrier of OCA.
If you and your partner have the same type of OCA your children will also have OCA.
- If you and your partner have different types of OCA your children with be carriers of both types of OCA.
- If your partner is a biological relative (cousin) there may be an increased chance that your child will have OCA.
OA has an X-linked recessive pattern of inheritance.
X-linked disorders only affect boys, but it is still possible for women to be carriers. An affected male will not have affected children, but all of his daughters will be carriers of OA. Women carriers are not affected, but have a 1 in 4 chance of having a child with OA. A male baby has a 50% (1 out of 2) chance of being affected.
Women carriers have an equal chance of the following pregnancy outcomes:
- 25% chance of an affected boy
- 25% chance of an unaffected boy
- 25% chance of a carrier daughter
- 25% chance of a daughter who is not a carrier
Molecular Genetic (DNA) testing
Genetic testing can help you make decisions about future children and help you understand your child’s albinism. As of 2011, scientists have identified four of the OCA genes and one OA gene.
Girls with albinism usually have OCA not OA and should be tested for the OCA genes.
Boys can have OA or OCA. Sometimes doctors can’t tell if a child’s hair and skin is affected by albinism just by looking at a child. Genetic testing may be able to tell which type of albinism your child has.
- Albinism is a genetic condition.
- There are two main types of albinism: OCA that affects the eyes, skin and hair and OA that affects only the eyes.
- OCA usually has an autosomal recessive inheritance pattern.
- OA has an x-linked recessive inheritance pattern. It affects only boys.
- Genetic testing can help you make decisions about future children