A Novel Mutation in CPT1A Resulting in Hepatic CPT Deficiency

The present work presents a "from gene defect to clinics" pathogenesis study of a patient with a hitherto unreported mutation in the CPT1A gene. In early childhood, the patient developed a life-threatening episode (hypoketotic hypoglycemia, liver cytolysis, and hepatomegaly) evocative of a mitochondrial fatty acid oxidation disorder, and presented deficient fibroblast carnitine palmitoyltransferase 1 (CPT1) activity and homozygosity for the c.1783 C > T nucleotide substitution on exon 15 of CPT1A (p.R595W mutant). While confirming CPT1A deficiency, whole blood de novo acylcarnitine synthesis and the levels of carnitine and its esters formally linked intracellular free-carnitine depletion to intracellular carnitine esterification. Sequence alignment and modeling of wild-type and p.*R595W CPT1A proteins indicated that the Arg595 targeted by the mutated codon is phylogenetically well conversed. It contributes to a hydrogen bond network with neighboring residues Cys304 and Met593 but does not participate in the catalysis and carnitine pocket. Its replacement by tryptophan induces steric hindrance with the side chain of Ile480 located in α-helix 12, affecting protein architecture and function. This hindrance with Ile480 is also originally described with tryptophan 304 in the known mutant p.C304W CPT1A, suggesting that the mechanisms that invalidate CPT1A activity and underlie pathogenesis could be common in both the new (p.R595W) and previously described (p.C304W) mutants.