Autosomal Dominant sight loss is due to a ‘fault’ (or mutation) in one gene, which is on one pair of autosomes. In other words, Autosomal Dominant sight loss occurs when a fault in only one copy of a gene is sufficient to cause sight loss. Genes that can cause Autosomal Dominant sight loss are often important for the structure of the retina.
Autosomal Dominant sight loss affects men and women equally, and can be passed on from an affected parent to a son or a daughter. A person with Autosomal Dominant sight loss has a one in two chance (50 per cent risk) of passing on the condition to one of their children. This is because he or she will contribute one chromosome from each pair to a child. Depending on whether the chromosome carries the faulty gene or its normal counterpart, the child may or may not be affected.
The chance of a child being affected is therefore 50:50 in each pregnancy; think of this as the tossing of a coin and the chance of the coin coming up heads. Chance has no memory and neither does nature. You have the same chance of a coin coming up heads irrespective of the number of times you have tossed it. In other words, if you have Autosomal Dominant sight loss and you already have a child with the condition, there is still a one in two chance of the next child being affected as well.
In some families, Autosomal Dominant sight loss has been known to exist for several generations while in others it may have been evident for only one or two generations. It does have to start somewhere so that some people who have no affected relatives may have Dominant sight loss although this in practice is not common.
Autosomal Dominant sight loss can be particularly variable, both between and within families, so some family members can be affected mildly and others more severely, irrespective of their ages. Occasionally the effects of Autosomal Dominant sight loss may appear to ‘skip a generation’ due to the variability in the severity of sight loss in different individuals or generations.