Electron Transport Chain

A 3-year-old child from rural Maharashtra presents with failure to thrive, developmental delay, and recurrent infections. Serum lactate is elevated at 8 mmol/L (normal <2), and pyruvate is 0.5 mmol/L. Muscle biopsy shows ragged-red fibres on Gomori trichrome stain. Which investigation is most appropriate to confirm the suspected mitochondrial cytopathy involving the electron transport chain?

A 28-year-old woman with a history of recurrent syncope and exercise intolerance is found to have a pathogenic heteroplasmic mutation in the mitochondrial ND4 gene (Complex I). Which investigation would best confirm the functional consequence of this mutation on electron transport chain activity?

Which is the most common cause of isolated Complex I deficiency in mitochondrial disease?

Which complex of the electron transport chain is the site of action of cyanide poisoning?

A 3-year-old boy from rural Maharashtra presents with progressive weakness, developmental delay, and recurrent infections. Serum lactate is 8 mmol/L (normal <2), and pyruvate is elevated. Muscle biopsy shows ragged-red fibres. Genetic testing confirms a mutation in MT-CO1 (mitochondrial cytochrome c oxidase subunit 1). What is the most appropriate immediate next step in management?