(6, 7). Although the enzyme defect is evident in tissues other than skeletal muscle (6,8), the disease usually presents only with the muscular symptomatology. More recently, though, CPTase II deficiency has been observed also in children and newborns presenting with hypoketotic hypoglycemia, cardiomyopathy, and sudden death (9-12).These observations indicate that CPTase II deficiency is a complex disorder with phenotypic heterogeneity that may reflect underlying heterogeneity at the molecular level. As a first step to understanding the molecular basis of CPTase deficiency, we have cloned the full-length cDNA of human CPTase II (13, 14). We now report the identification and characterization of the molecular defect in a patient with the early-onset form of CPTase II deficiency presenting with hypoketotic hypoglycemia and cardiomyopathy. 16.4%, 8.8%, and 6.6% of normal control in fibroblasts, lymphoblasts, and skeletal muscle, respectively (see Fig. 4A). Fibroblast CPTase II activity was also reduced by 40%o and 35% in the father and in the mother, respectively. PATIENTS AND METHODSAbbreviations: CPTase, carnitine palmitoyltransferase; nt, nucleotide(s).tTo whom reprint requests should be addressed. 8429The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.

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