Question

Jack and Jill are thinking about starting a family and they come to you with a question about a rare

recessive genetic disease called Alpers Syndrome. Alpers causes progressive neurodegeneration in

infants and children and is usually lethal within the first 10 years of life. Jack's grandfather had a brother

die of Alpers Syndrome, while Jill has no family history of the disease. If the frequency of heterozygotes

for Alpers is 1 in 2000 in the general population, what is the chance that Jack and Jill will have a child

with Alpers Syndrome?

The answer is not 0.

Answer 1

The possible alleles for Alper's syndrome are A and a. Because Alper's disease is autosomal (not sex-linked) recessive, it should be aa. Because Jill married into his family, it should be assumed that she is genotypically normal. If this is the case, then there should be a zero percent chance that her child with Jack will have the disease, even if Jack has it. This is because Jill's dominant alleles will protect the child from the disease. However, the child has 1/2 chance of being a carrier of the Alper's allele if Jack is a carrier, and a 1/1 chance of being a carrier if Jack has the disease.