Mitochondrial DNA depletion syndrome

Mitochondrial DNA depletion syndrome (MDS, also known as mtDNA depletion syndrome) is a group of severe, genetically heterogeneous disorders characterized by a significant reduction in mitochondrial DNA (mtDNA) copy number in affected tissues, leading to impaired mitochondrial energy production. Because mitochondria serve as the primary energy-generating organelles in cells, depletion of mtDNA results in defective oxidative phosphorylation and energy failure, predominantly affecting organs with high energy demands such as the brain, muscles, liver, and kidneys. MDS is classified into several clinical forms based on the primary organ systems involved: myopathic (affecting skeletal muscles, causing progressive muscle weakness, hypotonia, and feeding difficulties), hepatocerebral (affecting the liver and brain, presenting with liver failure, developmental delay, seizures, and neurological regression), encephalomyopathic (combining brain and muscle involvement), and neurogastrointestinal (affecting the nervous system and gastrointestinal tract). Onset is typically in infancy or early childhood, though some forms may present in the neonatal period. Common symptoms across subtypes include failure to thrive, progressive muscle weakness, lactic acidosis, developmental regression, and organ-specific dysfunction. MDS is caused by mutations in nuclear genes responsible for mtDNA maintenance and replication, including but not limited to POLG, DGUOK, TK2, SUCLA2, SUCLG1, RRM2B, TYMP, TWNK (previously C10orf2), and MPV17. Diagnosis is confirmed through genetic testing, measurement of mtDNA copy number in affected tissues, and assessment of respiratory chain enzyme activity. Treatment is primarily supportive and symptomatic, including nutritional support, management of organ failure, physical therapy, and seizure control. For the myopathic form caused by TK2 mutations, deoxynucleoside supplementation therapy has shown promise in clinical studies. Liver transplantation may be considered in select hepatocerebral cases, though outcomes vary. Prognosis depends on the subtype and severity, with many forms being progressive and life-limiting.

Data sourced from FDA regulatory filings and ClinicalTrials.gov. Updated periodically.

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