Combined 3-methylglutaconic and 3-hydroxy-3-methylglutaric aciduria with endocardial fibroelastosis and dilatative cardiomyopathy in male and female siblings with partial deficiency of complex II/III in fibroblasts.

We report on 2 children, brother and sister, who presented with cardiomyopathy and muscular hypotonia at the age of B months. They both excreted significant amounts of 3-hydroxy-3-methylglutaric acid (3-HMG) and 3-methylglutaconic acid (3-MGC) but no 3-methylglutaric acid (3-MG). Enzyme analysis in fibroblasts revealed normal activities of 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) lyase and of 3-methylglutaconyl hydratase and other enzymes of 3-HMG metabolism. Loading tests with leucine did not affect the excretion of 3-HMG and 3-MGC. The girl died as a result of her cardiomyopathy, while the boy recovered and was treated with cardiac supportive therapy. He showed a steady improvement during his clinical course with biochemical normalization of the urinary excretion of 3-HMG, concomitant with marked improvement in the hypertrophic cardiomyopathy. In cultured fibroblasts from both patients a reduced activity of complex II/III of the respiratory chain was measured which may be the cause of this new type of 3-HMG uria. Analysis of mitochondrial DNA heart muscle, liver and fibroblast culture of the patient did not reveal any major mitochondrial DNA rearrangements (deletion, duplication) or any point mutation that had been described in association with mitochondrial cardiomyopathy.