Objective: To characterize a distinct form of autosomal dominant cerebellar ataxia (ADCA) clinically and genetically. Background: ADCAs are a clinically, pathologically, and genetically heterogeneous group of neurodegenerative disorders. Nine responsible genes have been identified for SCA-1, -2, -3, -6, -7, -8, -10, and -12 and dentatorubral-pallidoluysian atrophy (DRPLA). Loci for SCA-4, -5, -11, -13, and -14 have been mapped. Methods: The authors studied a four-generation Japanese family with ADCA. The 19 members were enrolled in this study. The authors performed the mutation analysis by PCR and a genome-wide linkage analysis. Results: Nine members (five men and four women) were affected. The ages at onset ranged from 20 to 66 years. All affected members showed pure cerebellar ataxia, and three patients also had head tremor. Head MRI demonstrated cerebellar atrophy without brain stem involvement. The mutation analysis by PCR excluded diagnoses of SCA-1, -2, -3, -6, -7, -8, and -12 and DRPLA. The linkage analysis suggested linkage to a locus on chromosome 8q22.1-24.1, with the highest two-point lod score at D8S1804 (Z = 3.06 at θ = 0.0). The flanking markers D8S270 and D8S1720 defined a candidate region of an approximately 37.6-cM interval. This candidate region was different from the loci for SCA-4, -5, -10, -11, -13, and -14. Conclusion: The family studied had a genetically novel type of SCA (SCA-16).
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