combined oxidative phosphorylation defect type 15 (Monarch Disease Ontology entry MONDO_0013987) is a rare mitochondrial disease due to a defect in mitochondrial protein synthesis characterized by onset in infancy or early childhood of muscular hypotonia, gait ataxia, mild bilateral pyramidal tract signs, developmental delay (affecting mostly speech and coordination) and subsequent intellectual disability. Short stature, obesity, microcephaly, strabismus, nystagmus, reduced visual acuity, lactic acidosis, and a brain neuropathology consistent with Leigh syndrome are also reported. Also known as: COXPD15, MTFMT combined oxidative phosphorylation deficiency, combined oxidative phosphorylation deficiency caused by mutation in MTFMT, combined oxidative phosphorylation deficiency type 15.