Identification of five Spinocerebellar Ataxia Type 2 pedigrees in patientswith autosomal dominant cerebellar ataxia in Taiwan

Objectives - The autosomal dominant cerebellar ataxias (ADCAs) are a group of genetically diverse neurological conditions linked by progressive deteri oration in balance and coordination. Spinocerebellar Ataxia Type 2 (SCA2) i s one of the ADCAs and also belongs to a special group caused by the expans ion of an unstable CAG repeat encoding a polyglutamine tract. We aimed to i nvestigate the frequency of SCA2 mutation in the ataxia patients referred t o the clinic. Materials and methods - We screened 58 families with inherent cerebellar ataxia and 57 normal individuals by the use of radioactive geno mic polymerase chain reaction (PCR) method. A simple non-radioactive PCR fo r rapid detection of the expanded SCA2 alleles via agarose gel electrophore sis was also employed. Results - Eight SCA2 affected patients and 1 at-risk individual in 5 unrelated SCA2 families were identified. The CAG repeats o f normal alleles in the sample studied range in size from 16 to 30 repeat u nits, while those of SCA2 chromosomes are expanded to 34 to 49 repeat units . Our results also showed that unlike SCA1 and SCA3/MJD, the size distribut ion of the normal alleles showed few polymorphisms, with the 22 repeat alle le accounting for 90.1%. Homozygosity in normal individuals was 80.2%. No o verlap in ataxin-2 allele size between normal and expanded chromosomes was observed. Conclusion - This is the first report of the SCA2 gene distributi ons in the population of Taiwan. The SCA2 mutation accounts for 8.6% of ADC A type I families referred to us, intermediate between SCA1 (1.7%) and SCA3 /MJD (24%) of the ADCA type I families in our collection.