Research Notes: Isovaleric Acidemia

Background: Isovaleric acidemia results from a defect in the metabolism of the amino acid, leucine. The first patient with isovaleric acidemia was described in 1966 and the deficiency of isovaleryl-CoA dehydrogenase activity was found a few years later. Isovaleryl-CoA dehydrogenase functions in the inner mitochondrial matrix. The gene is located on chromosome 15.

Clinical: Isovaleryl-CoA dehydrogenase deficiency has two general presentations. The first occurs within days or weeks of life as an acute, overwhelming illness with vomiting and ketoacidosis progressing to lethargy, coma and death in greater than 50% of the patients. Other laboratory findings include variable hyperammonemia, hypocalcemia, neutropenia, thrombocytopenia, and pancytopenia. A second cohort has onset later in the first year of life or after. These patients develop chronic, intermittent illnesses brought on by infection or a large protein intake. Laboratory findings will be as noted above, but perhaps not so severe. Both groups are susceptible to infection. The patient commonly has a distinctive odor of "sweaty feet" during an illness because of the volatile isovaleric acid that accumulates.

Testing: Newborns can be screened for isovaleric acidemia using tandem mass spectrometry analysis of a heel-stick dried blood spot specimen. The finding of elevated five-carbon acylcarnitine (C5) indicates either isovaleryl-CoA dehydrogenase deficiency or 2-methylbutyryl-CoA dehydrogenase deficiency. To differentiate the two diseases, further testing is required. Urine organic acid analysis of a patient with isovaleric acidemia will reveal an elevation of isovalerylglycine with lesser elevation of 3-hydroxyisovaleric acid. The odiferous isovalerate is found in a urine specimen only during acute illness when its levels are significant. Due to its volatility (thus producing the odor), it is lost prior to and during specimen preparation for urine organic acid determination. In contrast, patients with 2-methylbutyryl-CoA dehydrogenase deficiency have 2-methylbutyrate and 2-methylbutyrylglycine in their urine. Prenatal diagnosis is possible by measuring isovalerylglycine in amniotic fluid and by measuring isovaleryl-CoA dehydrogenase enzyme activity in chorionic villus specimens or cultured amniocytes. The activity can also be measured in fibroblasts and leukocytes.

Treatment: Treatment of patients with isovaleric acidemia involves reducing protein intake, particularly the branched-chain amino acid leucine. During an acute episode, aggressive use of glucose and electrolytes is necessary. Glycine supplementation has proven beneficial because this amino acid is conjugated to isovalerate, forming the less harmful isovalerylglycine. Carnitine treatment is similarly effective. Strict dietary control and aggressive treatment have resulted in normal development in some patients. However, many patients with isovaleric acidemia show neurologic abnormalities from acute illness.

Because the diagnosis and therapy of isovaleric acidemia is complex, the pediatrician is advised to manage the patient in close collaboration with a consulting pediatric metabolic disease specialist and dietician. It is recommended that parents travel with a letter of treatment guidelines from the patient's physician.

Inheritance: This disorder most often follows an autosomal recessive inheritance pattern.

Cell Mol Neurobiol. 2007 Mar 30.
Isovaleric Acid Reduces Na(+), K (+)-ATPase Activity in Synaptic Membranes from Cerebral Cortex of Young Rats.
Ribeiro CA, Balestro F, Grando V, Wajner M.
Departamento de Bioquimica, Instituto de Ciencias Basicas da Saude, UFRGS, Porto Alegre, RS, Brazil.

1. Patients affected by isovaleric acidemia (IVAcidemia) suffer from acute episodes of encephalopathy. However, the mechanisms underlying the neuropathology of this disease are poorly known. The objective of the present study was to investigate the in vitro effects of the metabolites that predominantly accumulate in IVAcidemia, namely isovaleric acid (IVA), 3-hydroxyisovaleric acid (3-OHIVA) and isovalerylglycine (IVG), on important parameters of energy metabolism, such as (14)CO(2) production from acetate and the activities of the respiratory chain complexes I-IV, creatine kinase and Na(+), K(+)-ATPase in synaptic plasma membranes from cerebral cortex homogenates of 30-day-old rats. 2. We observed that 3-OHIVA acid and IVG did not affect all the parameters analyzed. Similarly, (14)CO(2) production from acetate (Krebs cycle activity), the activities of creatine kinase, and of the respiratory chain complexes was not modified by IVA. In contrast, IVA exposition to cortical homogenates provoked a marked inhibition of Na(+), K(+)-ATPase activity. However, this activity was not changed when IVA was directly exposed to purified synaptic plasma membranes, suggesting an indirect effect of this organic acid on the enzyme. Furthermore, pretreatment of cortical homogenates with alpha-tocopherol and creatine totally prevented IVA-induced inhibition on Na(+), K(+)-ATPase activity from synaptic plasma membranes, whereas glutathione (GSH) and the NO synthase inhibitor N(omega)-nitro-L: -arginine methyl ester (L-NAME) did not alter this inhibition. 3. These data indicate that peroxide radicals were probably involved in this inhibitory effect. Since Na(+), K(+)-ATPase is a critical enzyme for normal brain development and functioning and necessary to maintain neuronal excitability, it is presumed that the inhibitory effect of IVA on this activity may be involved in the pathophysiology of the neurological dysfunction of isovaleric acidemic patients.

Eur J Clin Nutr. 2007 Feb 7.
Amino-acid depletion induced by abnormal amino-acid conjugation and protein restriction in isovaleric acidemia.
Loots DT, Mienie LJ, Erasmus E.
1Department of Nutrition, School of Physiology, Nutrition and Consumers Science, Potchefstroom, South Africa.

Background: Previously, we detected 19 'new' amino-acid conjugates in the urine of patients with isovaleric acidemia. There is currently a poor understanding of the relationship between the clinical symptoms and the excreted metabolites occurring in these patients, owing to insufficient metabolite characterization and quantification. Consequently, controversial treatment protocols exist, particularly pertaining to dietary protein restriction. Objective: To determine the effect of the previously identified amino-acid conjugates and conventional dietary protein restriction therapy, on the free amino-acid concentrations in isovaleric acidemia patients, to better explain the clinical symptoms and develop more effective therapy. Design: Free amino-acid quantification via liquid chromatography mass spectrometry (LC-MS-MS) was performed on pre- and post-treatment urine or serum samples collected from six isovaleric acidemia patients, previously investigated for the presence of new induced N-isovaleryl and N-acetyl-amino-acid conjugates. Results: Depleted amino-acid concentrations were detected in varying degrees in all six patients and did not recover after conventional treatment. Conclusions: The 19 potentially toxic metabolites previously identified and the consequent amino-acid depletions detected in this study, may explain many of the clinical symptoms associated with isovaleric acidemia. Furthermore, the occurrence of amino-acid depletions in these patients, steers away from the controversial dietary protein restriction treatment protocols, and towards dietary leucine restriction alone with essential amino-acid supplementation, in combination with glycine and L-carnitine supplementation.

Acta Paediatr Taiwan. 2004 Jul-Aug.
Isovaleric acidemia diagnosed promptly by tandem mass spectrometry: report of one case.
Wei CC, Lin WD, Tsai FJ, Wu JY, Peng CT, Tsai CH.
Department of Pediatrics, China Medical University Hospital, Taichung, Taiwan.

Isovaleric acidemia (IVA), a recessive autosomal disorder, is caused by isovaleryl-CoA dehydrogenase deficiency. Isovaleric acidemia may present with symptoms during the acute stage of severe metabolic acidosis, ketosis, vomiting and altered mental status. This report concerns a 2-month-old female infant diagnosed as isovaleric acidemia by tandem mass spectrometry. She presented with two episodes of vomiting, poor activity and pancytopenia without obvious metabolic acidosis and hyperammonemia. She received combined therapy of L-carnitine, glycine and low protein and leucine diet. Hemogram and serum isovalerylcarnitine (IVC) were measured during the treatment. The depressed leukocyte and platelets recovered when serum isovalerylcarnitine level increased.

Pediatr Res. 1994 Aug.
Involvement of erythrocyte calpain in glycine- and carnitine-treated isovaleric acidemia.
Salamino F, Di Lisa F, Burlina AB, Menabo R, Barbato R, De Tullio R, Siliprandi N.
Istituto di Chimica Biologica, Universita di Genova, Italy.

When a 12-y-old girl suffering from isovaleric acidemia was treated with L-carnitine, there was a considerable increase in her blood and urine concentration of isovalerylcarnitine. When later the patient received an infusion of glycine in place of carnitine, isovalerylcarnitine reverted toward the low levels found in a normal subject. At the end of either treatment, erythrocyte calpain was measured and found to be decreased after carnitine therapy (140 versus 96 U/mg Hb with glycine or carnitine, respectively). Because we have previously shown that the activity of calpain isolated from erythrocytes was markedly modified by isovalerylcarnitine, the present results might be seen as the consequence of the chronic exposure of the patient's red blood cells to high levels of isovalerylcarnitine. The lowered calpain activity was also proved by an increase in erythrocyte band 3 phosphorylation together with an increased erythrocyte fragility after calcium loading in the presence of the ionophore A-23187. Calpastatin, the natural inhibitor of calpain, was only slightly modified.

Pediatr Res. 1994 Jan.
Intravenous L-carnitine and acetyl-L-carnitine in medium-chain acyl-coenzyme A dehydrogenase deficiency and isovaleric acidemia.
Van Hove JL, Kahler SG, Millington DS, Roe DS, Chace DH, Heales SJ, Roe CR.
Department of Pediatrics, Duke University Medical Center, Durham, North Carolina.

The purpose of this study was to determine whether treatment with L-carnitine or acetyl-L-carnitine enhances the turnover of lipid or branched-chain amino acid oxidation in patients with inborn errors of metabolism. Increasing i.v. doses of L-carnitine and acetyl-L-carnitine were given to one patient with medium-chain acyl-CoA dehydrogenase deficiency and to another with isovaleric acidemia. Both patients were in stable condition and receiving oral L-carnitine supplements. The excretion of carnitine and disease-specific metabolites was measured. The incorporation of L-carnitine in the intracellular pool was demonstrated using stable isotopes and mass spectrometry. Increasing doses of either i.v. L-carnitine or acetyl-L-carnitine did not stimulate the excretion of octanoylcarnitine in the patient with medium-chain acyl-CoA dehydrogenase deficiency, nor did it raise the plasma levels of either cis-4-decenoate or octanoylcarnitine. Similarly, increasing doses of either i.v. L-carnitine or acetyl-L-carnitine did not enhance the excretion of isovalerylcarnitine in a patient with isovaleric acidemia. The excretion of isovalerylglycine actually decreased. We conclude that there was no evidence of enhanced fatty acid beta-oxidation or enhanced branched-chain amino acid oxidation in vivo by the administration of high doses of L-carnitine or acetyl-L-carnitine in these two patients. Because only one individual with each disorder was studied, the data are only indicative and may not necessarily be representative of all individuals with these disorders. Definite settlement of this issue will require further studies in additional subjects.

Pediatr Res. 1988 Jul.
The treatment of isovaleric acidemia with glycine supplement.
Naglak M, Salvo R, Madsen K, Dembure P, Elsas L.
Emory University, Department of Pediatrics, Atlanta, Georgia.

Although dietary leucine restriction and supplemental glycine are used to treat patients with isovaleric acidemia [deficient isovaleryl-CoA-dehydrogenase (E.C.1.3.99.10)], little quantitative information is available regarding their optimum relationship. Herein we compare different glycine supplements and quantitate isovalerylglycine produced in two patients with clinically different forms of isovaleric acidemia during restricted leucine intake and during oral leucine loading. We found that under stable conditions of leucine restriction, 150 mg glycine/kg/day is an optimum glycine supplement and that glycine supplements of more than 250 mg/kg/day may result in reduced isovalerylglycine production; that when isovaleric acid accumulation is increased, glycine supplements to 600 mg/kg/day will increase isovalerylglycine production; and that the phenotype of isovaleric acidemia is related not only to the extent of impaired isovaleryl-CoA dehydrogenase, but also the ability to detoxify accumulated isovaleryl CoA to isovalerylglycine.

J Pediatr. 1988 Jul.
Isovaleric acidemia: medical and neurodevelopmental effects of long-term therapy.
Berry GT, Yudkoff M, Segal S.
Department of Pediatrics and Medicine, University of Pennsylvania School of Medicine, Philadelphia.

Nine patients with isovaleric acidemia were treated with a low-protein diet and supplemental glycine for up to 10 years. Carnitine was added to the therapy in four patients. Overall, the treatment was well tolerated, resulting in no significant side effects other than persistent hyperglycinemia. Normal growth was observed in all patients. Of four patients with the chronic phenotype, three, whose treatment was delayed beyond the first year of life, are mentally retarded. Two of five patients with the acute phenotype are retarded. The outcome in these two was complicated in one by neonatal intraventricular hemorrhage and in the other by therapeutic noncompliance. In our patients, only those who were treated successfully from early infancy and had no complications did not develop mental retardation. After initiation of therapy, there was a significant decrease in ketoacidotic attacks requiring hospitalization. Glycine is indicated for the treatment of acute ketoacidosis in these patients; none of the catastrophically ill newborn who received glycine died. The aim of treatment is to reduce the isovaleric acid burden to a minimum. Therapy consisting of leucine restriction with supplemental glycine and carnitine should be started as soon as possible after birth.

J Pediatr. 1987 Jan.
Endogenous catabolism is the major source of toxic metabolites in isovaleric acidemia.
Millington DS, Roe CR, Maltby DA, Inoue F.

A patient with isovaleryl-coenzyme A dehydrogenase deficiency was given a synthetic oral feed containing L-(2H3-methyl)-leucine of high isotopic purity as the only dietary precursor to the defective enzyme. Metabolites derived from this source were readily distinguished from their unlabeled endogenous counterparts by mass spectrometry. During 6 consecutive days of labeled leucine ingestion, the average daily excretion of labeled metabolites was only about 10% of the total derived from leucine. It is suggested that therapy should be directed toward the control of endogenous protein turnover rather than the restriction of dietary protein intake.

Enzyme. 1987.
Molecular basis of isovaleric acidemia and medium-chain acyl-CoA dehydrogenase deficiency.
Tanaka K, Ikeda Y, Matsubara Y, Hyman DB.
Department of Human Genetics, Yale University School of Medicine, New Haven, Conn.

Our early study of isovaleric acidemia (IVA) indicated that isovaleryl-CoA is dehydrogenated by an enzyme that is specific for isovaleryl-CoA. We subsequently identified and purified isovaleryl-CoA dehydrogenase (IVD) and 2-methyl-branched chain acyl-CoA dehydrogenase, which were previously unknown. We also purified and characterized three previously known acyl-CoA dehydrogenases. Five acyl-CoA dehydrogenases share similar molecular features and reaction mechanisms, indicating a close evolutionary relationship. Using the tritium release assay and [35S]methionine labeling/immunoprecipitation, we showed that IVA is due to a mutation of IVD. We also demonstrated that there are at least 5 distinct forms of mutant IVD, indicating an extensive molecular heterogeneity. Furthermore, we cloned cDNAs encoding IVD and medium-chain acyl-CoA dehydrogenases. The comparison of their complete primary sequences revealed a high degree of homology, indicating that these enzymes belong to a gene family, the acyl-CoA dehydrogenase family.

Pediatr Res. 1984 Dec.
Urinary excretion of l-carnitine and acylcarnitines by patients with disorders of organic acid metabolism: evidence for secondary insufficiency of l-carnitine.
Chalmers RA, Roe CR, Stacey TE, Hoppel CL.

Concentrations of l-carnitine and acylcarnitines have been determined in urine from patients with disorders of organic acid metabolism associated with an intramitochondrial accumulation of acyl-CoA intermediates. These included propionic acidemia, methylmalonic aciduria, isovaleric acidemia, multicarboxylase deficiency, 3-hydroxy-3-methylglutaric aciduria, methylacetoacetyl-CoA thiolase deficiency, and various dicarboxylic acidurias including glutaric aciduria, medium-chain acyl-CoA dehydrogenase deficiency, and multiple acyl-CoA dehydrogenase deficiency. In all cases, concentrations of acylcarnitines were greatly increased above normal with free carnitine concentrations ranging from undetectable to supranormal values. The ratios of acylcarnitine/carnitine were elevated above the normal value of 2.0 +/- 1.1. l-Carnitine was given to three of these patients; in each case, concentrations of plasma and urine carnitines increased accompanied by a marked increase in concentrations of short-chain acylcarnitines. These acylcarnitines have been examined using fast atom bombardment mass spectrometry in some of these diseases and have been shown to be propionylcarnitine in methylmalonic aciduria and propionic acidemia, isovalerylcarnitine in isovaleric acidemia, and hexanoylcarnitine and octanoylcarnitine in medium-chain acyl-CoA dehydrogenase deficiency. The excretion of these acylcarnitines is compatible with the known accumulation of the corresponding acyl-CoA esters in these diseases. In this group of disorders, the increased acylcarnitine/carnitine ratio in urine and plasma indicates an imbalance of mitochondrial mass action homeostasis and, hence, of acyl-CoA/CoA ratios. Despite naturally occurring attempts to increase endogeneous l-carnitine biosynthesis, there is insufficient carnitine available to restore the mass action ratio as demonstrated by the further increase in acylcarnitine excretion when patients were given oral l-carnitine.