Leigh syndrome is often associated with mitochondrial deficiencies that can be the result of over 100 different monogenetic disorders associated with mitochondrial OXPHOS dysfunction [12], although to date only two mitochondrial ribosomal subunit genes, MRPL44 and MRPS34, have been associated with Leigh syndrome [7, 14]. Here, MRPS34 is linked to hyperinsulinemic hypoglycemia, familial, 4.