Very-
long-chain acyl-coenzyme A dehydrogenase (
VLCAD) deficiency is an inborn mitochondrial
fatty-acid beta-oxidation (FAO) defect associated with a broad mutational spectrum, with phenotypes ranging from fatal cardiopathy in infancy to adolescent-onset
myopathy, and for which there is no established treatment. Recent data suggest that
bezafibrate could improve the FAO capacities in beta-oxidation-deficient cells, by enhancing the residual level of mutant
enzyme activity via gene-expression stimulation. Since
VLCAD-deficient patients frequently harbor missense mutations with unpredictable effects on
enzyme activity, we investigated the response to
bezafibrate as a function of genotype in 33
VLCAD-deficient fibroblasts representing 45 different mutations. Treatment with
bezafibrate (400 microM for 48 h) resulted in a marked increase in FAO capacities, often leading to restoration of normal values, for 21 genotypes that mainly corresponded to patients with the myopathic phenotype. In contrast,
bezafibrate induced no changes in FAO for 11 genotypes corresponding to severe neonatal or infantile phenotypes. This pattern of response was not due to differential inductions of
VLCAD messenger RNA, as shown by quantitative real-time polymerase chain reaction, but reflected variable increases in measured
VLCAD residual
enzyme activity in response to
bezafibrate. Genotype cross-analysis allowed the identification of alleles carrying missense mutations, which could account for these different pharmacological profiles and, on this basis, led to the characterization of 9 mild and 11 severe missense mutations. Altogether, the responses to
bezafibrate reflected the severity of the metabolic blockage in various genotypes, which appeared to be correlated with the phenotype, thus providing a new approach for analysis of genetic heterogeneity. Finally, this study emphasizes the potential of
bezafibrate, a widely prescribed
hypolipidemic drug, for the correction of
VLCAD deficiency and exemplifies the integration of molecular information in a therapeutic strategy.