Detection Methods and Status of CAT Interruption of ATXN1 in Korean Patients With Spinocerebellar Ataxia Type 1

Spinocerebellar ataxia type 1 (SCA1) is an autosomal dominant disease caused by abnormal CAG repeat expansion in the ataxin 1 gene (ATXN1). The presence of CAT interruption(s) is important for diagnosing SCA1 in patients with 39–44 repeat alleles, as only uninterrupted alleles are considered abnormal. Determining the CAT interruption status might also be important for patients with >44 repeats, as the length of the longest uninterrupted CAG repeat stretch has been correlated with age at SCA1 onset. We detected CAT interruption(s) in the archived samples of Korean SCA1 patients using a traditional restriction enzyme method and validated the usefulness of a fluorescence-based tethering PCR procedure. Among the 2,312 alleles analyzed from 1,156 patients, we found 17 expanded alleles with ≥39 repeats, 71% of which harbored 39–44 repeats. Restriction enzyme method of six samples (four with 39–44 repeats and two with >44 repeats) revealed that none of the expanded alleles had CAT interruption(s). Tethering PCR showed the characteristic electropherogram pattern expected without CAT interruption(s). Along with the enzyme restriction method, tethering PCR can be applied to determine the number of allele repeats and provide information on CAT interruption(s) in clinical laboratories.