Molecular heterogeneity of autosomal dominant cerebellar ataxia: analysis of flanking microsatellites of the spinocerebellar ataxia 1 locus in a northern European family unequivocally demonstrates non-linkage.

This study addresses the question whether the different forms of autosomal dominant cerebellar ataxia (ADCA) are related to different ethnic/geographical regions in Europe. One mutation in families originating from Holland, Prussia and Italy has previously been localized to chromosome 6p (SCA1 locus), whereas the mutation in families of Iberic origin has been excluded from chromosome 6p. In a Danish five-generation pedigree with ADCA and in which previous HLA-serotyping had shown inconclusive linkage results, the present study shows unequivocal exclusion from the SCA1 locus, firstly through the use of the new, highly informative microsatellites D6S89 and D6S109, which closely flank the SCA1 locus, and secondly through the manifestation of disease in four pedigree members previously scored as unaffected. Additional molecular genetic analysis of the HLA DRbeta and F13A polymorphisms also argue against a cluster of ADCA genes on chromosome 6p. Since this study demonstrates the existence of non-SCA1 families and therefore heterogeneity in the North-European population, molecular family counselling remains restricted to the few known SCA1 families.