The genotype–phenotype study of the PRDM12 polyalanine tract shows that having 7–15 alanines is normal; 16–18 alanines is associated with MiTES; 19 alanines leads to CIP; and no clinically atypical cases of MiTES had a polyalanine tract expansion. Here, PRDM12 is linked to hereditary sensory and autonomic neuropathy.