In CPI II deficiency, long-chain acylcarnitines are transported across the inner mitochondrial membrane but cannot be converted to their corresponding long-chain acyl- CoAs. They accumulate in the mitochondrial matrix and are transported out into plasma. Ihese elevated levels may produce cardiac arrhythmias. Dicarboxylicaciduria is absent, because of the same explanation given for carnitine transport defect. Ihe exact incidence is unknown, but the adult form is more common than the infantile form. Risk factors are fasting and prolonged exercise.
Ihere are two presentations: the adult muscular form, in which prolonged exercise induces weakness and myoglobinuria, and a severe infantile form, in which nonketotic hypoglycemic coma without dicarboxylicaciduria, seizures, hepatomegaly, cardiomegaly, and cardiac arrhythmia are accompanied by low plasma and tissue levels of carnitine with increase in long-chain acylcarnitines. Ihe classic adult form is autosomal recessive and usually affects males between 15 and 30 years of age. Ihe serum creatine kinase value is normal between episodes, carnitine levels are usually normal in plasma and tissues, and long-term muscle weakness is rare, although lipid storage may be seen on muscle biopsy. Ihe differential diagnosis includes other carnitine cycle disorders. Management involves supportive treatment of the renal failure and measures to remove the myoglobin from kidney and avoidance of triggering factors-prolonged exercise, exposure to cold, infections, and fasting. Presentation in the neonatal period usually ends in death. In the adult form, about a fourth of patients develop renal failure secondary to the episodic myoglobinuria.
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