Overview of repeats
Repeat mutations in the PRDM12 gene have been shown to be one of the causes of the hereditary sensory and autonomic neuropathy type VIII (HSAN8) (Chen et al., 2015). Patients with homozygous alleles of 18 and 19 alanine repeats have been defined, while in the general population the length of alleles does not exceed 14 alanine repeats (Chen et al., 2015).
In some cases, the type of repeats causing HSAN8 has been classified as imperfect GCN (Khristich & Mirkin, 2020; Lavoie et al., 2003). However, we consider repeats in this locus as the standard type due to the fact that in both affected and unaffected individuals, the allele consists of alanines coded by GCC repeat units only, except the last residue that is coded by GCG (Chen et al., 2015). This means that the repeat expansion in patients resulted in extended stretch of only GCC repeats, and therefore do not have the characteristics of imperfect GCN types of repeats.