CYP2U1 and External ophthalmoplegia: The potential role of CYP2U1 in mitochondrial function and the onset of MacTel is consistent with recent findings by Birtel et al49 who reported 2 cases of chronic progressive external ophthalmoplegia associated with sporadic single mtDNA deletions (m.11037_14597del), demonstrating some phenotypic characteristics associated with MacTel.