Overview of repeats
Expansion of GGC repeats in the ZFHX3 gene in exon 10 leading to SCA4 has been identified independently in several studies. In one of them, the repeat expansions in SCA4 patients were found to be 45 GGC repeats or longer, all of which were uninterrupted (Figueroa et al., 2024). The second study reported that expanded alleles in affected individuals were 42–72 GGC repeats in length as determined from short-read WGS data (Wallenius et al., 2024). Finally, the third study showed that individuals with the disease have repeats between 48 and 57 GGC repeats (Chen et al., 2024). ZFHX3 repeat lengths in non-expanded alleles were reported to be 14-26 (Wallenius et al., 2024) and 15-31 in the control cohort of another study (Chen et al., 2024), with the most common length being 21.