We ultimately identified 41 mutations, of which 37 were novel, in 20 genes that were previously reported to cause OXPHOS disease and 3 novel mitochondria-related genes (MRPS23, QRSL1, and PNPLA4) as causative genes of mitochondrial respiratory chain complex deficiencies. Here, MRPS23 is linked to hyperinsulinemic hypoglycemia, familial, 4.