MT-ND4L and Leber hereditary optic neuropathy: Further molecular genetics analyses included a gene dosage analysis of OPA1 using multiplex ligation-dependent probe amplification (MLPA), as well as Sanger sequencing of MT-ND1, MT-ND2, MT-ND4, MT-ND4L and MT-ND6, which include all mitochondrial mutations in LHON described to date.