Prenatal diagnosis of Machado-Joseph disease by direct mutation analysis

MJD is the most frequent dominant ataxia and an incapacitating disorder. Onset is most frequently during the reproductive years, and genetic counselling is its only means of prevention. The causative mutation—an expansion of a (CAG)n on chromosome 14q32.1—can now be directly detected. We now report the first two cases of prenatal diagnosis (PND). The first presented as a simultaneous request for predictive testing and PND at 14 weeks of pregnancy. Owing to time constraints, we performed a full protocol of counselling with shorter intervals between sessions, while psycho‐social evaluation of the other parent and obstetric consults were also begun. We ensured that the couple wished termination if the fetus was a carrier, to avoid a presymptomatic test for the unborn child. We were thus able to deliver test results two weeks before PND. As the fetus carried an expanded allele (77 CAGs) inherited from his father, termination was performed and the couple received counselling, psychological and social support. The second case was the fetus of a carrier‐mother that was diagnosed as non‐carrier, also after amniocentesis. © 1998 John Wiley & Sons, Ltd.