Early-onset nystagmus often occurs in families, but by no means always. When nystagmus runs in families, the chance that a new baby will be affected with nystagmus depends on the specific inheritance pattern that is associated with the specific underlying diagnosis, not simply the presence of nystagmus. In some children the nystagmus appears not to be inherited, but it may be due to a random change in a gene, in which case the child will start a new line of inheritance. In other children with nystagmus, there is no obvious inheritance pattern, and it just seems to happen for unknown reasons.

WHAT ARE THE PATTERNS OF INHERITANCE?

Every child has 23 pairs of chromosomes (46 chromosomes in all), one of each pair is inherited from the child’s father and the other of each pair from the child’s mother. One pair are special, the X and Y chromosomes, since they determine the sex of the child, and are called the sex chromosomes. The other 44 are called autosomes.

Some of the conditions that give rise to nystagmus are due to a single gene defect, and usually follow a distinct pattern of inheritance. There are three main type of single-gene inheritance patterns: a) autosomal recessive, b) autosomal dominant, and c) X-linked recessive (sometimes called ‘sex-linked’ inheritance). Each has a different pattern of inheritance, which depends on the underlying visual disorder – not specifically on the presence of nystagmus.

It should be remembered that you have absolutely no control over which genes are passed on to you, or which genes you pass on to your children – it is just like rolling dice.