severe X-linked mitochondrial encephalomyopathy (MONDO_0010437) is an extremely rare mitochondrial respiratory chain disease resulting in a neurodegenerative disorder characterized by psychomotor delay, hypotonia, areflexia, muscle weakness and wasting in the two patients reported to date. Also known as: combined oxidative phosphorylation deficiency 6, X-linked recessive, combined oxidative phosphorylation deficiency type 6, mitochondrial encephalomyopathy due to COXPD6, mitochondrial encephalomyopathy due to combined oxidative phosphorylation defect 6.