Combined Oxidative Phosphorylation Deficiency 55 (COXPD55)

OMIM number: 619743

Comments closing date: 26/09/2025

Combined Oxidative Phosphorylation Deficiency 55 (COXPD55) is a rare, variable hereditary
(genetic) condition which causes developmental delay, short stature and decreased muscle tone,
and learning disabilities, typically in childhood. It is caused by an alteration (also called “pathogenic
variant”) in one or both copies of gene called POLRMT. The POLRMT gene has an important
role within mitochondria and when altered, disrupts the cells’ ability to make energy. Symptoms typically being in infancy and childhood, but have been reported in adulthood. Symptoms include developmental delay, brain abnormalities and seizures; reduced muscle tone, muscle weakness and short stature; vision problems. People affected by this condition can have variable features, but unfortunately, most are expected to be significantly impacted. There is currently no cure for COXPD55, and treatment focuses on managing symptoms and supporting affected individuals.

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