REFINEMENT OF THE LOCUS FOR AUTOSOMAL-DOMINANT CEREBELLAR-ATAXIA TYPE-II TO CHROMOSOME 3P21.1-14.1

We have previously mapped the gene for autosomal dominant cerebellar a taxia type II (ADCAII) to chromosome 3p12-p21.1 in a region of 33 cM b y using four families of different geographic origin. In this study, w e analysed the families with nine additional simple tandem repeat mark ers located in the ADCAII candidate region. An extensive clinical eval uation was also performed in the Belgian family CA-1 on two probably a ffected and seven at-risk individuals by means of ophthalmological exa mination and magnetic resonance imaging. Based on informative recombin ants, we were able to reduce the ADCAII candidate region to the 12-cM region between D3S1300 and D3S1285. Furthermore, haplotype analysis am ong the families suggested that the most likely location of the ADCAII gene is within the 6.2-cM interval between D3S3698 and D3S1285. Becau se of the documented anticipation in ADCAII families, we also analysed family CA-1 with six polymorphic triplet repeat markers located on ch romosome 3. None of these markers showed expanded alleles.