A comparison of in vitro acylcarnitine profiling methods for the diagnosis of classical and variant short chain acyl-CoA dehydrogenase deficiency.

Homozygosity and compound heterozygosity for the short chain acyl-CoA dehydrogenase (SCAD) gene sequence variants 625G-->A and 511C-->T are associated with ethylmalonic aciduria (EMA), a biochemical indicator of SCAD deficiency. The clinical and biochemical implications of these variants are not fully understood. The effect of these variants on the accumulation of butyrylcarnitine by fibroblasts in culture was studied. In vitro acylcarnitine profiling in fibroblasts was carried out using [U-13C]-labeled or unlabeled palmitate in the presence of excess L-carnitine, with or without a medium chain acyl-CoA dehydrogenase (MCAD) inhibitor. Acylcarnitines were analyzed using tandem mass spectrometry. 625G/625G (wild type), 625G/625A and 625A/625A (variant) control fibroblasts were compared with fibroblasts from patients homozygous for inactivating SCAD mutations (SCAD deficient) and from patients with EMA who were homozygous or compound heterozygous for the SCAD variants. Variant control and patient fibroblasts accumulated moderate amounts of butyrylcarnitine compared with wild-type controls and in contrast to the significant amount of butyrylcarnitine accumulated by SCAD deficient fibroblasts, regardless of incubation conditions. Moderately reduced SCAD activity associated with SCAD variants can be detected using in vitro acylcarnitine profiling methods, which may be used as an indirect measure of SCAD activity.