Heterogeneity of carnitine-palmitoyltransferase deficiency

Episodes with muscle ache, rhabdomyolysis and myoglobinuria with or without associated renal insufficiency are characteristic of muscle carnitine-palmitoyltransferase (CPT) deficiency. However, patients differ from each other in many aspects, such as the kind of stimulus that triggers rhabdomyolysis, the ability to produce ketone bodies when fasting, whether the enzyme defect is localized in skeletal muscle or is general, and the nature of the enzyme defect, which may be in CPT I or CPT II or both. Studies of muscle, liver and fibroblasts from a patient with recurrent rhabdomyolysis spontaneously occurring or triggered by exercise or fever, revealed a CPT deficiency in the muscle and liver biopsy samples but normal CPT activity in cultured cells, differing from previously reported patients. The enzyme defect in muscle was evidenced by two different methods, but not when determined with a method that measures the formation of palmitoylcarnitine. The enzyme abnormality in the patient's liver was associated with a delayed ketone body production and with a dramatic increase in long-chain acylcarnitines in the serum when fasting. Moreover the patient was unable to build up ketones when fed long-chain triglycerides (LCT) but showed prompt ketogenic response when fed medium-chain triglycerides (MCT). The heterogeneity of clinical presentations and of the biochemical findings in patients with CPT deficiency are discussed.