Carnitine palmitoyl transferase II deficiency, myopathic form

Carnitine palmitoyl transferase II (CPT II) deficiency, myopathic form, is the most common and mildest presentation of CPT II deficiency, a rare inherited disorder of long-chain fatty acid oxidation. CPT II is an enzyme located on the inner mitochondrial membrane that is essential for transporting long-chain fatty acids into the mitochondria, where they are broken down to produce energy. In the myopathic form, the enzyme has reduced but not absent activity, primarily affecting skeletal muscle. This form is also sometimes referred to as the 'adult' or 'muscular' form of CPT II deficiency. The hallmark symptom is recurrent episodes of muscle pain (myalgia), muscle stiffness, and exercise intolerance, often accompanied by rhabdomyolysis — the breakdown of muscle tissue that releases a protein called myoglobin into the blood, which can lead to dark-colored urine (myoglobinuria) and, in severe cases, acute kidney failure. Episodes are typically triggered by prolonged exercise, fasting, cold exposure, infection, emotional stress, or sleep deprivation. Between episodes, patients usually have normal muscle strength and no symptoms. The condition predominantly affects males, though females can also be affected. The age of onset is typically in adolescence or young adulthood, though childhood onset has been reported. Diagnosis is confirmed through enzyme activity assays and genetic testing of the CPT2 gene. A common pathogenic variant, p.Ser113Leu, is found in a large proportion of patients with the myopathic form. Management focuses on prevention of episodes through dietary modifications, including a high-carbohydrate, low-long-chain-fat diet, avoidance of known triggers such as prolonged fasting and intense exercise, and supplementation with medium-chain triglycerides (MCT) as an alternative energy source. Intravenous glucose and hydration are used during acute rhabdomyolysis episodes to protect kidney function. With appropriate lifestyle modifications, the long-term prognosis is generally favorable.

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