Clinical and genetic analysis of a Tunisian family with autosomal dominant cerebellar ataxia type 1linked to the SCA2 locus

Autosomal dominant cerebellar ataxias (ADCA) type 1 are a clinically and genetically heterogeneous group of neurodegenerative disorders. We report a large Tunisian ADCA type 1 family in which 17 patients (mean age at onset ± SD = 35.6. ± 15.3 years) were examined. There was mean anticipation of 10.3 ± 15.4 years in this family; anticipation was greater in paternal (28 ± 8.2 years) than in maternal (2.7 ± 10.9 years) transmission. Linkage analysis performed with microsatellite markers linked to the spinal cerebellar ataxia 1 (SCA1) locus on chromosome 6p and the SCA2 locus on chromosome 12q excluded linkage to SCA1, but there was close linkage with marker D12S105 (Zmax = 2.51 at 6 = 0.00). This result was confirmed by multipoint analysis, which generated a maximal lod score of 3.46 at this locus. Multipoint analysis and haplotype reconstruction reduced the interval containing the SCA2 locus to 6.4 cM, a narrowing of the 35-cM interval in a previously described Cuban SCA2 family with a clinical picture similar to that of our family, including a high frequency of postural and action tremor.