Occurrence of hyperammonemia in the course of 17 cases of methylmalonic acidemia

Methylmalonic and propionic acidemias: clinical management update

PURPOSE OF REVIEW

Recent clinical studies and management guidelines for the treatment of the organic acidopathies methylmalonic acidemia (MMA) and propionic acidemia address the scope of interventions to maximize health and quality of life. Unfortunately, these disorders continue to cause significant morbidity and mortality due to acute and chronic systemic and end-organ injury.

RECENT FINDINGS

Dietary management with medical foods has been a mainstay of therapy for decades, yet well controlled patients can manifest growth, development, cardiac, ophthalmological, renal, and neurological complications. Patients with organic acidopathies suffer metabolic brain injury that targets specific regions of the basal ganglia in a distinctive pattern, and these injuries may occur even with optimal management during metabolic stress. Liver transplantation has improved quality of life and metabolic stability, yet transplantation in this population does not entirely prevent brain injury or the development of optic neuropathy and cardiac disease.

SUMMARY

Management guidelines should identify necessary screening for patients with methylmalonic acidemia and propionic acidemia, and improve anticipatory management of progressive end-organ disease. Liver transplantation improves overall metabolic control, but injury to nonregenerative tissues may not be mitigated. Continued use of medical foods in these patients requires prospective studies to demonstrate evidence of benefit in a controlled manner.

Growth retardation, general hypotonia, and loss of acquired neuromotor skills in the infants of mothers with cobalamin deficiency and the possible role of succinyl-CoA and glycine in the pathogenesis

Vitamin B12 (cobalamin, Cbl) deficiency can cause metabolic, hematological, and neurological abnormalities. Adequate levels of succinyl-coenzyme A (CoA) cannot be synthesized from methylmalonyl-CoA because of the decreased activity of the methylmalonyl-CoA mutase enzyme that uses Cbl as the cofactor. Succinyl-CoA synthesis deficiency leads to decreased heme synthesis and gluconeogenesis. The reason of growth retardation can be gluconeogenesis deficiency together with heme synthesis deficiency whereas the reason of the neurological abnormalities can be glycine increase in the tissue due to decreased heme synthesis. We present 7 infants diagnosed with severe nutritional Cbl deficiency and discuss the role of succinyl-CoA and glycine in the possible pathogenesis in this article. Patients brought to our clinic with a complaint of growth retardation and diagnosed with nutritional Cbl deficiency were included in the study. There were 5 females and 2 males. The mean age was 11 ± 2.30 (range 6-13) months. All patients had general muscular hypotonia and 4 had growth retardation. Neuromotor growth retardation was found in 4 of the children who had previously shown normal neuromotor development for age. The mean Cbl level was 83.8 ± 27.6 (45.6-114) pg/mL. The mean Cbl level of the mothers was 155 ± 56.6 (88-258) pg/mL. Six of the patients had anemia and 1 had thrombocytopenia. Mean corpuscular volume value was 91.5 ± 12.2 fL. Following treatment, the muscle tonus of the patients improved, the anemia and growth retardation decreased, and the lost neuromotor abilities were recovered. Severe nutritional Cbl deficiency is an important nutritional disease where complications can be prevented with early treatment. When evaluating the pathogenesis, it should be noted that nutritional Cbl deficiency is a succinyl-CoA synthesis deficiency.

α-Ketoglutaramate: an overlooked metabolite of glutamine and a biomarker for hepatic encephalopathy and inborn errors of the urea cycle

Glutamine metabolism is generally regarded as proceeding via glutaminase-catalyzed hydrolysis to glutamate and ammonia, followed by conversion of glutamate to α-ketoglutarate catalyzed by glutamate dehydrogenase or by a glutamate-linked aminotransferase (transaminase). However, another pathway exists for the conversion of glutamine to α-ketoglutarate that is often overlooked, but is widely distributed in nature. This pathway, referred to as the glutaminase II pathway, consists of a glutamine transaminase coupled to ω-amidase. Transamination of glutamine results in formation of the corresponding α-keto acid, namely, α-ketoglutaramate (KGM). KGM is hydrolyzed by ω-amidase to α-ketoglutarate and ammonia. The net glutaminase II reaction is: L - Glutamine + α - keto acid + H2O → α - ketoglutarate + L - amino acid + ammonia. In this mini-review the biochemical importance of the glutaminase II pathway is summarized, with emphasis on the key component KGM. Forty years ago it was noted that the concentration of KGM is increased in the cerebrospinal fluid (CSF) of patients with hepatic encephalopathy (HE) and that the level of KGM in the CSF correlates well with the degree of encephalopathy. In more recent work, we have shown that KGM is markedly elevated in the urine of patients with inborn errors of the urea cycle. It is suggested that KGM may be a useful biomarker for many hyperammonemic diseases including hepatic encephalopathy, inborn errors of the urea cycle, citrin deficiency and lysinuric protein intolerance.

Effects of a single dose of N-carbamylglutamate on the rate of ureagenesis

We studied the effect on ureagenesis of a single dose of N-carbamylglutamate (NCG) in healthy young adults who received a constant infusion (300 min) of NaH(13)CO(3). Isotope ratio-mass spectrometry was used to measure the appearance of label in [(13)C]urea. At 90 min after initiating the H(13)CO3-infusion each subject took a single dose of NCG (50 mg/kg). In 5/6 studies the administration of NCG increased the formation of [(13)C]urea. Treatment with NCG significantly diminished the concentration of blood alanine, but not that of glutamine or arginine. The blood glucose concentration was unaffected by NCG administration. No untoward side effects were observed. The data indicate that treatment with NCG stimulates ureagenesis and could be useful in clinical settings of acute hyperammonemia of various etiologies.

Clinical approach to inherited metabolic diseases in the neonatal period: a 20-year survey

Every newborn with unexplained neurological deterioration, ketosis, metabolic acidosis or hypoglycaemia should be suspected of having an inherited error of intermediary metabolism. Many of these conditions can be diagnosed clinically with the aid of simple laboratory investigations. Since a substantial number of these diseases respond well to treatment but may otherwise be fatal, and in order to assure adequate prenatal diagnosis in subsequent pregnancies, a high index of suspicion and rapid diagnosis are necessary in the face of the clinical presentations described. According to three major clinical presentations observed in 218 neonates with inborn errors of intermediary metabolism (neurological distress 'intoxication' type, neurological distress 'energy-deficiency' type and hypoglycaemia with liver dysfunction) and according to the proper use of few laboratory investigations, we propose a method of diagnosis which groups these children into five categories. Initial therapy, and sophisticated investigations can be planned on the basis of this grouping.

3-Hydroxy-3-methylglutaryl-coenzyme A lyase deficiency: report of five new patients

Five new patients are reported and the pathogenesis of the hypoglycaemia without ketogenesis is discussed. This report extends a recent review.

Hyperammonemia

A symptomatic elevation in plasma ammonium concentration, termed hyperammonemia, is associated with numerous congenital and acquired conditions (Table 11). In some cases, such as urea cycle disorders, ammonia is the principal toxin. In other instances, such as portal systemic encephalopathy, it is but one of a number of metabolic disturbances, However, in either case hyperammonemic episodes should be treated aggressively to prevent coma, subsequent brain damage, or death. This involves restricting protein intake, providing adequate calories, and giving agents that remove accumulated nitrogen. Long-term therapy relies on diagnosing the specific disease rate. This rarely requires invasive procedures such as liver biopsy. In most cases measurement of plasma amino acids and urinary organic acids will identify the defect. Treatment involving restriction of nitrogen intake, vitamin supplementation, or stimulation of alternative pathways of waste nitrogen excretion can then be instituted. Early therapy, especially in patients with neonatal-onset hyperammonemia, is imperative to avoid severe brain damage. On this basis, the plasma ammonium level should be determined in virtually every newborn with lethargy, hypotonia, poor feeding, seizures, and/or respiratory distress of unclear origin (Table 12).

Hudson memorial lecture. Neonatal management of organic acidurias. Clinical update

Therapeutic guidelines have been obtained from a retrospective review of 41 patients affected with organic acidaemias, 16 patients with neonatal maple syrup urine disease (MSUD), 11 methylmalonic acidaemia, (MMA) seven propionic acidaemias (PA) and seven isovaleric acidaemias (IVA), and by comparing this personal series with similar reported cases. The emergency treatment of these organic acidurias in the neonate has to main goals: toxin removal and anabolism. Anabolism is always promoted by early diet therapy. The best method of toxin removal depends on the nature of the defect; peritoneal dialysis with exchange transfusions or multiple or prolonged exchange transfusions in MSUD and in PA, diuresis and exchange transfusions in MMA and glycine supplementation in IVA. Vitamin supplementation (thiamine 20 mg, biotin 10 mg, B12 2 mg and riboflavin 100 mg) should be tried in all cases although the neonatal forms of these defects are very rarely vitamin responsive. Additional treatments such as carnitine or insulin may prove to be useful.

Characterization of enzymatic deficiencies of branched chain amino-acid catabolism in human fibroblasts by genetic complementation

Leucine and Isoleucine metabolism in cultured skin fibroblasts from patients with leucinosis, beta-Ketothiolase deficiency, propionic, methylmalonic and isovaleric acidemia, was compared with that in normal fibroblasts. A simple assay was developed using (U14C) Isoleucine and (U14C) Leucine as substrates. Radioactive incorporation into protein aminoacids were measured. The (U14C) branched chain aminoacid incorporation into proteins provides an estimation of the protein synthesis and the incorporation ratio (14C) Aspartate + (14C) Glutamate/(14C) branched chain aminoacid, measures the integrity of the metabolic pathway. Complementation tests permits to characterize the genetic defect. The incorporation ratio was significantly decreased in blocked pathways, namely in leucinosis and isovaleric acidemia in the presence of (U14C) Leucine and in Leucinosis, beta-Ketothiolase deficiency, propionic and methylmalonic acidemia in the presence of (U14C) Isoleucine. There was a significant restoration of activity in mutant strains with distinct genetic defects after polyethylene-glycol fusion. This assay provides a valuable tool to screen for enzymatic deficiencies of branched chain aminoacid catabolism.