Combined oxidative phosphorylation defect type 4

Combined oxidative phosphorylation deficiency type 4 (COXPD4) is an extremely rare autosomal recessive mitochondrial disorder caused by mutations in the TUFM gene, which encodes the mitochondrial translation elongation factor Tu (EF-Tu). This protein is essential for mitochondrial protein synthesis, and its dysfunction leads to impaired assembly and activity of multiple oxidative phosphorylation (OXPHOS) enzyme complexes. Because oxidative phosphorylation is the primary means by which cells generate energy, deficiency in this pathway has devastating consequences for high-energy-demand tissues, particularly the brain, muscles, and liver. Clinical features of COXPD4 typically present in the neonatal or early infantile period and include severe lactic acidosis, progressive encephalopathy, and rapidly progressive neurological deterioration. Affected infants may exhibit hypotonia, feeding difficulties, respiratory insufficiency, and failure to thrive. Brain imaging often reveals leukoencephalopathy or other structural abnormalities. Liver dysfunction and cardiomyopathy may also be present. The clinical course is generally severe, with most reported patients experiencing rapid decline and early death. There is currently no curative treatment for COXPD4. Management is supportive and symptomatic, focusing on nutritional support, management of lactic acidosis, seizure control if applicable, and respiratory support. Some clinicians may trial mitochondrial cofactors or vitamins (such as coenzyme Q10, riboflavin, or thiamine), though evidence for their efficacy in this specific condition is lacking. Genetic counseling is recommended for affected families.

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