Enzymology of the branched-chain amino acid oxidation disorders: the valine pathway

Valine is one of the three branched-chain amino acids which undergoes oxidation within mitochondria. In this paper, we describe the current state of knowledge with respect to the enzymology of the valine oxidation pathway and the different disorders affecting oxidation

Clinical, biochemical, and molecular findings in three patients with 3-hydroxyisobutyric aciduria

3-Hydroxyisobutyric aciduria is a rare entity and affected individuals display a range of clinical manifestations including dysmorphic features and neurodevelopmental problems in the majority of patients. Here, we present two novel patients with 3-hydroxyisobutyric aciduria. To our knowledge, these are the 11th and 12th cases of 3-hydroxyisobutyic aciduria reported. It is believed that a deficiency in 3-hydroxyisobutyrate dehydrogenase is the most likely cause of this disorder. Measurement of 3-hydroxyisobutyrate dehydrogenase activity in fibroblasts homogenates of the two newly identified patients and a previously reported patient, however, revealed similar activities as in control fibroblasts. Since other enzymes with overlapping substrate specificity could conceal abnormal 3-hydroxyisobutyrate dehydrogenase activity, we cloned a candidate human cDNA for 3-hydroxyisobutyrate dehydrogenase (HIBADH). By heterologous expression in Escherichia coli, we showed that the product of the HIBADH gene indeed displays 3-hydroxyisobutyrate dehydrogenase activity. Mutation analysis of the corresponding gene in the patients suffering from 3-hydroxyisobutyric aciduria revealed no mutations. We conclude that HIBADH is not the causative gene in 3-hydroxyisobutyric aciduria

Clinical, biochemical, and molecular findings in three patients with 3-hydroxyisobutyric aciduria

3-Hydroxyisobutyric aciduria is a rare entity and affected individuals display a range of clinical manifestations including dysmorphic features and neurodevelopmental problems in the majority of patients. Here, we present two novel patients with 3-hydroxyisobutyric aciduria. To our knowledge, these are the 11th and 12th cases of 3-hydroxyisobutyic aciduria reported. It is believed that a deficiency in 3-hydroxyisobutyrate dehydrogenase is the most likely cause of this disorder. Measurement of 3-hydroxyisobutyrate dehydrogenase activity in fibroblasts homogenates of the two newly identified patients and a previously reported patient, however, revealed similar activities as in control fibroblasts. Since other enzymes with overlapping substrate specificity could conceal abnormal 3-hydroxyisobutyrate dehydrogenase activity, we cloned a candidate human cDNA for 3-hydroxyisobutyrate dehydrogenase (HIBADH). By heterologous expression in Escherichia coli, we showed that the product of the HIBADH gene indeed displays 3-hydroxyisobutyrate dehydrogenase activity. Mutation analysis of the corresponding gene in the patients suffering from 3-hydroxyisobutyric aciduria revealed no mutations. We conclude that HIBADH is not the causative gene in 3-hydroxyisobutyric aciduri

Hypertrophic cardiomyopathy, cataract, developmental delay, lactic acidosis: a novel subtype of 3-methylglutaconic aciduria

3-Methylglutaconic aciduria is the biochemical marker of several inherited metabolic diseases. Four types of 3-methylglutaconic aciduria can be distinguished. In the type I form, accumulation of 3-methylglutaconate is due to deficient activity of 3-methylglutaconyl-CoA hydratase, an enzyme of the leucine degradation pathway. In the other forms, 3-methylglutaconic acid is not derived from leucine but is of unidentified origin, possibly derived from other metabolic pathways, such as mevalonate metabolism. We report five patients, all presenting a severe early-onset phenotype characterized by 3-methylglutaconic aciduria, hypertrophic cardiomyopathy, cataract, hypotonia/developmental delay, lactic acidosis, and normal 3-methylglutaconyl-CoA hydratase activity. This peculiar phenotype, for which a primary mitochondrial disorder is hypothesized, identifies a novel subtype of 3-methylglutaconic aciduri

Mutations in the gene encoding 3-hydroxyisobutyryl-CoA hydrolase results in progressive infantile neurodegeneration

Only a single patient with 3-hydroxyisobutyryl-CoA hydrolase deficiency has been described in the literature, and the molecular basis of this inborn error of valine catabolism has remained unknown until now. Here, we present a second patient with 3-hydroxyisobutyryl-CoA hydrolase deficiency, who was identified through blood spot acylcarnitine analysis showing persistently increased levels of hydroxy-C(4)-carnitine. Both patients manifested hypotonia, poor feeding, motor delay, and subsequent neurological regression in infancy. Additional features in the newly identified patient included episodes of ketoacidosis and Leigh-like changes in the basal ganglia on a magnetic resonance imaging scan. In cultured skin fibroblasts from both patients, the 3-hydroxyisobutyryl-CoA hydrolase activity was deficient, and virtually no 3-hydroxyisobutyryl-CoA hydrolase protein could be detected by western blotting. Molecular analysis in both patients uncovered mutations in the HIBCH gene, including one missense mutation in a conserved part of the protein and two mutations affecting splicing. A carefully interpreted acylcarnitine profile will allow more patients with 3-hydroxyisobutyryl-CoA hydrolase deficiency to be diagnose