Malonyl CoA decarboxylase deficiency: C to T transition in intron 2 of theMCD gene

Malonyl CoA decarboxylase (MCD) is an enzyme involved in the metabolism of fatty acids synthesis. Based on reports of MCD deficiency, this enzyme is p articular important in muscle and brain metabolism. Mutations in the MCD ge ne result in a deficiency of MCD activity, that lead to psychomotor retarda tion, cardiomyopathy and neonatal death. To date however, only a few patien ts have been reported with defects in MCD. We report here studies of a pati ent with MCD deficiency, who presented with hypotonia, cardiomyopathy and p sychomotor retardation. DNA sequencing of MCD revealed a homozygous introni c mutation, specifically a -5 C to T transition near the acceptor site for exon 3. RT-PCR amplification of exons 2 and 3 revealed that although mRNA f rom a normal control sample yielded one major DNA band, the mutant mRNA sam ple resulted in two distinct DNA fragments. Sequencing of the patient's two RT-PCR products revealed that the larger molecular weight fragments contai ned exons 2 and 3 as well as the intervening intronic sequence. The smaller size band from the patient contained the properly spliced exons, similar t o the normal control. Western blotting analysis of the expressed protein sh owed only a faint band in the patient sample in contrast to a robust band i n the control. In addition, the enzyme activity of the mutant protein was l ower than that of the control protein. The data indicate that homozygous mu tation in intron 2 disrupt normal splicing of the gene, leading to lower ex pression of the MCD protein and MCD deficiency. J. Neurosci. Res. 65:591-59 4, 2001. (C) 2001 Wiley-Liss, Inc.