[SCA1, SCA2, MJD/SCA3 (CAG)n mutation detection and analysis in patients with hereditary spinocerebellar ataxia from Chinese families].

OBJECTIVE

To assess the frequency of the SCA1, SCA2, MJD/SCA3 CAG trinucleotide repeat expansions ((CAG)n) among individuals diagnosed with hereditary spinocerebellar ataxia (SCA) from Chinese families.

METHOD: The SCA1, SCA2, MJD/SCA3 (CAG)n mutation were detected with the polymerose chain reaction (PCR), denaturing polyacrylamide gel and silver staining technique in 79 patients with autosomal dominant SCA from 50 Chinese families.

RESULTS

Among 50 kindreds, 2% (1/50) had the SCA1, (CAG)n, 6% (3/50) had the SCA2, (CAG)n, whereas 48% (24/50) were positive for the MJD/SCA3 (CAG)n. Thus, together SCA1, SCA2, and MJD/SCA3 represent 56% (28/50) of the autosomal dominant ataxias in our group. In two SCA1 patients the CAG repeat was expanded to 53-62 repeats, whereas in normal ivdividuals was 12-36 repeats. In seven SCA2 patients the CAG repeat was expanded to 43-47 repeats, whereas in normal ivdividuals was 22-30 repeats. In forty-two MJD/SCA3 patients the CAG repeat was expanded to 63-78 repeats, whereas in normal ivdividuals was 15-38 repeats. The SCA1, SCA2, MJD/SCA3 (CAG)n mutation were excluded in the other 28 SCA patients from 22 families.

CONCLUSION

The frequency of MJD/SCA3 is substantially higher than that of SCA1 and SCA2 in the autosomal dominant SCA from Chinese families. Chinese patients with MJD/SCA3 are non-Portuguese patients with MJD/SCA3. Clinical expressions of the various SCAs overlap one another, making a diagnostic classification based on phenotype inaccurate in many instances. It is important for SCA clinical study to make a SCA gene diagnosis and genomic classification.