3-Hydroxyisobutyric acid dehydrogenase deficiency: Expanding the clinical spectrum and quantitation of D- and L-3-Hydroxyisobutyric acid by an LC-MS/MS method.

A deficiency of 3-hydroxyisobutyric acid dehydrogenase (HIBADH) has been recently identified as a cause of primary 3-hydroxyisobutyric aciduria in two siblings; the only previously recognized primary cause had been a deficiency of methylmalonic semialdehyde dehydrogenase, the enzyme that is immediately downstream of HIBADH in the valine catabolic pathway and is encoded by the ALDH6A1 gene. Here we report on three additional patients from two unrelated families who present with marked and persistent elevations of urine L-3-hydroxyisobutyric acid (L-3HIBA) and a range of clinical findings. Molecular genetic analyses revealed novel, homozygous variants in the HIBADH gene that are private within each family. Evidence for pathogenicity of the identified variants is presented, including enzymatic deficiency of HIBADH in patient fibroblasts. This report describes new variants in HIBADH as an underlying cause of primary 3-hydroxyisobutyric aciduria and expands the clinical spectrum of this recently identified inborn error of valine metabolism. Additionally, we describe a quantitative method for the measurement of D- and L-3HIBA in plasma and urine and present the results of a valine restriction therapy in one of the patients.

Clinical and biochemical characterization of 3-hydroxyisobutyryl-CoA hydrolase (HIBCH) deficiency that causes Leigh-like disease and ketoacidosis.

3-Hydroxyisobutyryl-CoA hydrolase (HIBCH) deficiency is an autosomal recessive disorder characterized by episodes of ketoacidosis and a Leigh-like basal ganglia disease, without high concentrations of pyruvate and lactate in the cerebrospinal fluid. Only 4 cases of HIBCH deficiency have been reported. However, clinical-biochemical correlation in HIBCH deficiency by determining the detailed residual enzyme activities has not yet been elucidated. Here, we report a case of two Japanese siblings with HIBCH deficiency carrying a new homozygous missense mutation (c.287C > A, [p.A96D]) at the substrate-binding site. A transfection study using HIBCH expression vectors harboring wild type or 4 reported mutations, including the newly identified mutation (p.A96D, p.Y122C, p.G317E, and p.K74Lfs*13), revealed a correlation between residual HIBCH activities and the severity of the disease. All HIBCH mutants, except p.K74Lfs*13, showed residual enzyme activity and only the patient with p.K74Lfs*13 had congenital anomalies. p.G317E showed only low enzyme activity (~ 3%) of that of wild-type HIBCH. Although p.A96D had approximately 7 times higher enzyme activity than p.G317E, patients with p.A96D died during childhood. These findings are essential for clinical management, genetic counseling, and specific meal and concomitant drug considerations as part of the treatment for patients with HIBCH deficiency.