Mitochondrial disorders (MDs) are among the most common inborn errors of metabolism, and dysfunction in oxidative phosphorylation (OXPHOS) is a hallmark. Their complex mode of inheritance and diverse clinical presentations render the diagnosis of MDs challenging, and, to date, most lack a cure. Here, we build on previous efforts to identify genes necessary for OXPHOS and report a highly complementary galactose-sensitized CRISPR-Cas9 growth screen, presenting an updated inventory of 481 OXPHOS genes, including 157 linked to MDs. We further focus on FAM136A, a gene associated with Ménière's disease, and demonstrate that it supports intermembrane space protein homeostasis and OXPHOS in cell lines, mice, and patients. Our study identifies a mitochondrial basis in familial Ménière's disease, provides a comprehensive resource of OXPHOS-related genes, and sheds light on the pathways involved in MDs, with the potential to guide future diagnostics and treatments for MDs.