Evidence for the existence of a fourth dominantly inherited spinocerebellar ataxia locus.

The autosomal dominantly inherited spinocerebellar ataxias (SCAs) are a heterogeneous group of disorders. To date, three loci have been identified: the SCA1 locus (on chr 6p), the SCA2 locus (on chr 12q), and more recently a Machado-Joseph disease (MJD) locus (on chr 14q). We have studied one large French-Canadian kindred with four generations of living affected individuals segregating an autosomal dominant form of SCA. Linkage analysis using anonymous DNA markers that flank the three previously described loci significantly exclude the French-Canadian kindred from the SCA1, SCA2, and MJD loci. Therefore, a fourth, still unmapped SCA locus remains to be identified. In addition, the unique clinical phenotype present in all affected individuals of the French-Canadian kindred might be characteristic of this still unmapped SCA locus.