Novel pathogenic <i><scp>COX</scp>20</i> variants causing dysarthria, ataxia, and sensory neuropathy

<i>COX20/FAM36A</i> encodes a mitochondrial complex IV assembly factor important for COX2 activation. Only one homozygous <i>COX20</i> missense mutation has been previously described in two separate consanguineous families. We report four subjects with features that include childhood hypotonia, areflexia, ataxia, dysarthria, dystonia, and sensory neuropathy. Exome sequencing in all four subjects identified the same novel <i>COX20</i> variants. One variant affected the splice donor site of intron-one (c.41A>G), while the other variant (c.157+3G>C) affected the splice donor site of intron-two. cDNA and protein analysis indicated that no full-length cDNA or protein was generated. These subjects expand the phenotype associated with COX20 deficiency.