Tay-Sachs, Sandhoff, GM-1, Canavan and most related allied diseases are
autosomal recessive diseases.
Autosomal means the disease affects males and females equally. Recessive means both parents must be a carrier for a child to be at risk. Carriers do not have any adverse health effects.
High-risk couples, in which the man and the woman are carriers of the same genetic condition, have a 25% chance with each pregnancy of conceiving a child with that condition. There is a 50% chance of producing a child who is a carrier like the parents and a 25% chance that the child will be neither a carrier nor affected with the disease.
If only one parent is a carrier, there is no chance of producing a baby with a recessive disease. There is, however, a 50% chance in each pregnancy that the child will be a carrier.
A few of the allied diseases such as Fabry and Pelizaeus Merzbacher Disease are X-linked diseases. The term X-linked refers to the location of the genes causing these diseases on the X
chromosome, which means they typically only affect males. Recently female carriers have been recognized as also experiencing symptoms.
A carrier female of an X-linked condition may pass on either of her X chromosomes to her children. On average, half of her sons will be affected, and half of her sons will not be affected. Half of her daughters will be carriers, and half will not be carriers and therefore will have no chance of having a child with the condition.
