3-hydroxypropionate: significance of -oxidation of propionate in patients with propionic acidemia and methylmalonic acidemia

Glutaric aciduria: clinical and laboratory findings in two brothers

In two siblings with dystonic cerebral palsy the urinary metabolic profiles of organic acids were dominated by glutaric acid, a metabolite not normally present in urine. The exretion of glutaric acid amounted to several grams per day. The urinary excretion of beta-OH-glutaric acid and glutaconic acid was also enhanced. Imparied metabolism of glutaryl-CoA by leukocytes indicates that the patients suffer from an inborn error of lysine, tryptophan, and hydroxylysine metabolism. A defective oxidation of glutaryl-CoA to crotonyl-CoA, probably due to a deficiency of glutaryl-CoA dehydrogenase, is consistent with these findings.

[Methylmalonic aciduria. Classification, diagnosis and therapy (author's transl)]

Congenital methylmalonic aciduria (MMA) is a metabolic disorder inherited by an autosomal recessive trait. The metabolic block is located in the catabolic pathway of propionyl-CoA to succinyl-CoA. Biochemically, four enzymatic defects have been recognized, i.e.: 1. Methylmalonyl-CoA racemase. 2. Methylmalonyl-CoA mutase apoenzyme. 3. Synthesis of desoxyadenosyl-cobalamine. 4. Disturbance at an earlier level of cobalamine metabolism which causes defective synthesis of both vitamin B12-coenzymes. These four enzymatic defects express themselves in three ways: non-vitamin B12-dependent MMA (defects 1 and 2); vitamin B12-dependent MMA (defect 3); MMA associated with homocystinuria (defect 4). The various forms of MMA cannot be distinguished clinically from one another. The disorder manifests itself during the first few days to weeks of life. Principal symptoms and signs are: anorexia, vomiting, muscular hypotonia and metabolic acidosis. The diagnosis is established by determination of methylmalonic acid in plasma, cerebrospinal fluid and urine, as well as by assay of enzyme activities in leukocytes, liver tissue or cultured fibroblasts (from biopsied skin). A prenatal diagnosis is feasible by the examination of cultured amnion cells, amniotic fluid and maternal urine. Therapy of non vitamin B12-dependent MMA calls for reduction of protein intake, particularly that of precursors of methylmalonic acid, such as methionine, threonine, isoleucine and valine. The treatment of vitamin B12-dependent forms is accomplished by i.m. injection of high doses of vitamin B12. No definite statement can be made as yet with regard to long-term prognosis and normalcy of mental development in treated children.

[13C]Valine metabolism in methylmalonicacidemia using nuclear magnetic resonance: propinonate as an obligate intermediate

[Alpha-13C]- and [alpha,beta-13C]valine were administered sequentially to a patient with methylmalonicacidemia to clarify the metabolic pathway of valine from methylmalonic acid semialdehyde to methylmalonyl-CoA. Methylmalonic acid was isolated from multiple urine samples, purified, and analyzed by 13C nuclear magnetic resonance spectroscopy. Contrary to the widely accepted view, the results show unequivocally that methylmalonic acid semialdehyde is decarboxylated to propionate before conversion to methylmalonyl CoA.