|Number of repeats||Counts (alleles)||Percentage|
Overview of repeats
Normal range of repeats in ATXN1 gene was considered to be in the range of 6-39 repeats and where CAG expansions beyond 39 repeats were linked to the spinocerebellar ataxia type 1 (SCA1) (Orr et al., 1993). Another research by Zuhlke et al (2002) which analysed repeat lengths in the range of 36 to 43 triplets showed the importance of CAT interruptions in the pathogenicity of an allele. For example, individuals who had 39 triplets in their allele and no CAT interruptions had characteristic features for SCA1 whereas individuals with CAT interruptions did not. Additionally, they showed that individuals with alleles 36-38 repeats had ataxia but no SCA1 phenotype (Zuhlke et al., 2002). Recently there are reports showing the potential risk factor of intermediate length alleles (at least 33 CAG repeats) on the ALS (Lattante et al., 2018) as well as on progressive non-fluent aphasia (PNFA) (Rosas et al., 2020).