|Number of repeats||Counts (alleles)||Percentage|
Overview of repeats
In a healthy population, CAG repeats in the ATXN7 gene ranges from 4-35, whereas expansions of 37 or more repeats cause spinocerebellar ataxia type 7 (Stevanin et al., 1998). Repeats between 28 and 35 increases risk of pathogenic alleles during meiosis which would result in SCA7 in offspring (Gousse et al., 2018), but repeats in this range are extremely rare (Stevanin et al., 1998). However, a study conducted on Mexican population discovered SCA7 patients who had alleles comprised as less as 34 repeats (Magaña et al., 2014).