FASTKD2-related infantile mitochondrial encephalomyopathy

FASTKD2-related infantile mitochondrial encephalomyopathy is an extremely rare autosomal recessive mitochondrial disorder caused by mutations in the FASTKD2 gene (also known as FAST kinase domain-containing protein 2). This gene plays a critical role in mitochondrial RNA processing and is essential for proper mitochondrial respiratory chain function. When FASTKD2 is deficient, cells cannot produce energy efficiently, leading to dysfunction in energy-demanding tissues such as the brain and skeletal muscles. The disease typically presents in infancy with a combination of encephalopathy (brain dysfunction) and myopathy (muscle weakness). Key clinical features include developmental delay or regression, seizures, hemiplegia (weakness on one side of the body), and episodes of neurological deterioration often triggered by febrile illness. Brain imaging may show abnormalities consistent with mitochondrial disease, including signal changes in the basal ganglia and brainstem. Elevated lactate levels in blood or cerebrospinal fluid may be observed, reflecting impaired mitochondrial energy metabolism. Muscle biopsy may reveal cytochrome c oxidase (complex IV) deficiency. There is currently no cure or disease-specific treatment for FASTKD2-related infantile mitochondrial encephalomyopathy. Management is supportive and symptomatic, focusing on seizure control with antiepileptic medications, physical therapy for motor impairment, nutritional support, and avoidance of metabolic stressors such as prolonged fasting or high fevers. Some clinicians may trial mitochondrial cofactor supplementation (such as coenzyme Q10, riboflavin, or L-carnitine), though evidence for efficacy in this specific condition is limited. The prognosis is variable but can be severe, with significant neurological disability.

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