Recently, a homozygous mutation in individuals from two unrelated families displaying ataxia and muscle hypotonia was found in a gene (FAM36A) homologous to the yeast gene COX20 (Szklarczyk et al., 2013), which has previously been shown to encode a protein that assists membrane insertion and maturation of the COXII subunit of CIV (Elliott et al., 2012). Here, COX20 is linked to cerebellar ataxia.