Predictive testing in the context of pregnancy: experience in Huntington's disease and autosomal dominant cerebellar ataxia.

Presymptomatic (PT) and prenatal testing (PNT) for Huntington’s disease (HD) have been available since 1986. Testing was initially based on genetic markers linked to the disease locus on chromosome 4p. Since 1993 and the identification of the huntingtin gene, direct analysis provides accurate PT and PNT. Recent advances in the field of molecular genetics has provided suitable tools for direct testing in an increasing number of hereditary neurodegenerative disorders, such as autosomal dominant cerebellar ataxias (SCA for spinocerebellar ataxias). Huntington’s disease and SCA are both associated with severe neurological handicap and a progressive course of the disease. The onset is usually in adulthood and many people at risk have already completed their families when requesting PT. However, for others, future family planning is a frequent motive for requesting PT, either because subjects at risk do not want to give birth to a child with a 50% risk of being affected, or because they would rather not have children if they were a carrier. Several authors have studied the incidence of pregnancy and PNT after PT and showed that the frequency of PNT was quite low among adult onset diseases. In contrast, pregnancies in couples at risk who were requesting PT has not been studied. For the parents, the situation is stressful because of the lack of sufficient preparation for an unfavourable result