I already have one child with Canavan disease, what is the chance that I will have a second child with the condition?
One in four, or 25% chance. Canavan disease is inherited in an autosomal recessive pattern, meaning that both parents of a child with the disorder likely carry a change in the ASPA gene. The parents have one working copy of the gene and one nonworking copy; they are carriers for Canavan disease. Both parents must pass along a nonworking copy of the gene. For each individual pregnancy, there is a 25% chance that both parents will pass along a nonworking copy of the gene and the child will have the disorder. There is a 50% chance that one parent will pass on the gene change and the other won't, meaning the child will be a carrier for the disorder. There is a 25% chance that both parents will pass along a working copy of the gene and the child will not have the disorder and will not be a carrier.