A 28-year-old woman from Delhi with a 6-month history of progressive fatigue, dyspnea on exertion, and recurrent infections is found to have a serum lactate of 6 mmol/L (normal <2) and pyruvate of 0.3 mmol/L (normal <0.1) at rest. Muscle biopsy shows ragged-red fibers and electron microscopy reveals abnormal mitochondrial morphology. Genetic sequencing confirms a heteroplasmic mutation in the mitochondrial DNA-encoded NADH dehydrogenase (Complex I) gene. She is currently on standard supportive care. What is the most appropriate immediate next step in management?