Mary is a 27 year old woman who is very involved in the mucopolysaccahidosis (MPS)
support group. Mary’s sister, Jane, died of Hurler syndrome (alpha-L-iduronidase
deficiency) at age 8 years. Mary met two very nice men at the support group meeting, Joe
and Bob, both of whom are affected with a MPS disorder. Joe has Scheie syndrome
(alpha-L-iduronidase deficiency) and Bob has a mild form of Hunter syndrome (iduronate
sulfatase deficiency). All of the defects are verified by enzyme testing. Mary is actively
dating both Joe and Bob and wants to know her chances of having a child affected with a
MPS disorder before deciding which man to marry.

If Mary marries Joe, what is the chance they would have a child affected with a MPS
disorder: