Isobutyryl-CoA dehydrogenase deficiency: isobutyrylglycinuria and ACAD8 gene mutations in two infants.

Isobutyryl-CoA dehydrogenase (IBD) is an enzyme involved in the catabolism of the branched-chain amino acid valine. We report a third and a fourth child with IBD deficiency who were both detected during newborn screening with tandem mass spectrometry and so far do not receive any treatment. The diagnosis was confirmed by biochemical and molecular studies. One of the children is homozygous for the mutation M128I in the ACAD8 gene, which is predicted to affect the substrate binding cavity. The other child is compound heterozygous for a frameshift mutation F33fsins and a missense mutation V203I. It is as yet uncertain whether IBD deficiency may cause significant morbidity in affected children and whether treatment is necessary. In view of the limited experience worldwide, careful monitoring of the children is recommended.