Objective: To study the clinical characteristics and molecular biology of hereditary spinocerebellar ataxia type 7 (SCA7).
Methods: Peripheral blood samples were collected from 245 with autosomal dominant SCA from 184 families and 71 sporadic SCA patients. Polymerase chain reaction, polyacrylamide gel electrophoresis, and capillary electrophoresis technique were used to detect the SCA7 (CAG) n trinucleotide repeat mutations. 163 healthy persons were used as controls. The abnormal allele fragments were sequenced by ABI 377 DNA sequencing machine.
Results: Three SCA families with 15 patients were identified with a positive rate of 1.6%. DNA sequencing showed that the abnormal SCA7 alleles with CAG repeat were expanded to 38 to 71 repeats, and the normal SCA7 alleles were carried from 6 to 15 CAG repeats. Analysis of parent-child couples demonstrated the existence of marked anticipation in 2 families, especially in paternal transmission. Linkage analysis found a maximum two-point LOD score of 2.82 in the microsatellite D3S1300 at recombination fraction (theta = 0.00).
Conclusion: CAG expansion is the pathogenic cause of SCA7, a rare subtype of SCA. The 38 CAG is the minimum pathological expansion in mainland China.