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 ataxia type II (ADCAII) to chromosome 3p12-p21.1 in a region of 33 cM by using four families of different geographic origin. In this study, we analysed the families with nine additional simple tandem repeat markers located in the ADCAII candidate region. An extensive clinical evaluation was also performed in the Belgian family CA-1 on two probably affected and seven at-risk individuals by means of ophthalmological examination and magnetic resonance imaging. Based on informative recombinants, we were able to reduce the ADCAII candidate region to the 12-cM region between D3S1300 and D3S1285. Furthermore, haplotype analysis among the families suggested that the most likely location of the ADCAII gene is within the 6.2-cM interval between D3S3698 and D3S1285. Because of the documented anticipation in ADCAII families, we also analysed family CA-1 with six polymorphic triplet repeat markers located on chromosome 3. None of these markers showed expanded alleles.