Features of carnitine palmitoyltransferase type I deficiency

Carnitine palmitoyltransferase type I (CPT I) is unique among long-chain fa tty acid oxidation enzymes in that there are two tissue-specific isoforms, 'hepatic' and 'muscle', which are encoded by two separate genes. The 'hepat ic' isoform is expressed in liver, kidney and fibroblasts and at low levels in the heart, while the other isoform occurs in skeletal muscle and is the predominant form in heart. Reported patients with CPT I deficiency lack ac tivity of the hepatic isoform and present before 30 months of age with hypo ketotic hypoglycaemia, hepatomegaly with raised transaminases, seizures and coma. We discuss four new cases in three families showing, variously, rena l tubular acidosis, transient hyperlipidaemia and, paradoxically, myopathy with elevated creatinine kinase or cardiac involvement in the neonatal peri od as additional features that deserve wider recognition.