FDXR and multiple mitochondrial dysfunctions syndrome 9b: FDXR (OMIM: 103270) variants FDXR c.364C>T (p.Arg122Cys) and c.1069G>T (p.Val357Leu) could cause auditory neuropathy and optic atrophy (OMIM: 617717) or multiple mitochondrial dysfunction syndrome 9B (OMIM: 620887).