Dominant spinocerebellar ataxia: genetic counseling.

Dominantly inherited spinocerebellar ataxia (OPCA 1) poses a particular problem for genetic counseling due to late age of onset. Liability for disease using observed age of onset can be combined with HLA linkage data to provide revised estimates of risk for affection. Where data is informative, certain combinations may yield estimates which improve so rapidly with age that postponement of childbearing may become a strong consideration as an option.