ATXN2 and amyotrophic lateral sclerosis: The effect of (CCG)2CCC (encoding poly-proline tail varying from 1–4) on CAG instability and possibly ALS phenotype should be also considered as it may contribute to both to the CAG (in)stability increasing the number of continuous triplets folding as hairpin, and to the content of prolines residues which lowers the complexity of unstructured sequence regions in the N-terminal tail of ataxin-2 [41].