Comparative frequency and severity of hypoglycemia in selected organic acidemias, branched chain amino acidemia, and disorders of fructose metabolism

Impaired glucose homeostasis and a novel HLCS pathogenic variant in holocarboxylase synthetase deficiency: a report of two cases and brief review

Objectives Holocarboxylase synthetase deficiency (HCSD) (OMIM #253270) is a rare inborn error of metabolism with an estimated annual incidence of 1 in 200,000 people. Typical manifestations of HCSD include eczema, alopecia, lactic acidosis and hyperammonemia. Diagnosis is made through genetic analysis. Case presentation Patient 1 was a 7-year-old girl with normal growth and development, presenting with severe hypoglycemia and metabolic acidosis. Her family reported that she was diagnosed as having ketotic hypoglycemia; she had five episodes of hypoglycemia and metabolic acidosis in past 4 years when her oral intake decreased during acute illness. Patient 2 was a 6-month-old female infant with normal growth and development, presenting with progressive generalized eczema and metabolic acidosis for the first time. We found that they both had hyperammonemia, hyperlactatemia, hyperketonemia, organic acids detected in urine and elevated C5OH acylcarnitine level by tandem mass spectrometry. HLCS gene analysis showed a homozygous pathogenic variant p.V363D in patient 1 and a pathogenic variant p.R508W compound with a novel splice site pathogenic variant c.2010-1G>A in patient 2. They have been on biotin treatment (10 mg/day for both of them) for more than 2 years and no more symptoms have occurred. Conclusions HCSD is a rare disease, and it can be fatal if severe metabolic acidosis occurs without timely management. Once the diagnosis is made, most of the patients with HCSD have good prognosis and normal life expectancy with biotin treatment.

Long Term Follow-Up of Polish Patients with Isovaleric Aciduria. Clinical and Molecular Delineation of Isovaleric Aciduria

Isovaleric acidemia (IVA) is an autosomal recessive leucine inborn error of metabolism caused by isovaleryl-CoA dehydrogenase deficiency. The disease has various courses, from severe ones manifesting in newborns to the intermittent form with first manifestation in children and adults. The aim of this study was to analyze clinical and neurological outcomes in Polish patients with IVA. Ten patients diagnosed and treated in The Children's Memorial Health Institute were included in the study. The diagnosis was based on tandem MS (increased level of C5 acylcarnitine) and urine GCMS (increased isovalerylglycine, and 3-hydroxyisovaleric acid). Molecular analysis was performed in seven patients (70%) leading to the detection of pathogenic variants in the IVD gene in all of them. A retrospective analysis of patients' medical records included: demographics, symptoms at diagnosis, medical management, and biochemical and clinical outcomes following therapy. The median follow-up time (median; Q1-Q2) was 2.5 years (1.5-9.0) for newborn screening (NBS) and family screening (FS) children, and 17 years (5.0-20) for symptomatic patients. Five patients were in a good clinical state, four children presented mild neurological symptoms, and one-severely delayed child. In the IVD gene, five known and two novel variants (p.466C>G, c.1132G>A) were identified. Molecular analysis was performed in seven patients leading to identification of biallelic pathogenic variants in the IVD gene in all of them. We can conclude that long-term clinical and neurological outcomes of patients with IVA were satisfactory as a result of an early diagnosis and proper management. Although early treatment did not prevent decompensations, they were milder in these patients.

Defect of cobalamin intracellular metabolism presenting as diabetic ketoacidosis: a rare manifestation

Hypoglycemia is the usual feature of commonly occurring organic acidemias. Organic acidemias manifesting as hyperglycemia or diabetic ketoacidosis are rare and only a few cases have been reported. We report a 13-month-old boy who presented with vomiting, dehydration, coma, hyperglycemia, high anion gap metabolic acidosis and ketosis, mimicking diabetic ketoacidosis (DKA). Treatment with parenteral fluid, electrolytes, and insulin infusion resulted in an improvement in hyperglycemia, but persistence of metabolic acidosis and lack of improvement of neurologic status led us to suspect an organic acidemia. Urinary organic acid analysis revealed increased methylmalonic acid levels. In addition, hyperhomocysteinemia and homocystinuria were also noted in presence of normal vitamin B12 levels. This confirmed the diagnosis of cobalamin metabolism defect leading to combined methylmalonic aciduria and homocystinuria. There was some improvement in neurologic status and metabolic parameters after treatment with low-protein diet, vitamin B12, folic acid, and L-carnitine, but he ultimately succumbed to polymicrobial nosocomial sepsis. The entire MMACHC gene of the patient was sequenced and no mutations were identified. This is probably the first case report of cobalamin intracellular metabolism defect (CblC/CblD/CblF/CblJ or ABCD4) presenting as diabetic ketoacidosis.

Propionic acidemia mimicking diabetic ketoacidosis

Propionic acidemia manifesting with hyperglycemia is rare. Few cases have been reported mainly of the neonatal-onset form associated with high mortality. We report a 9-month-old Palestinian boy who manifested with coma, severe hyperglycemia and ketoacidosis mimicking diabetic ketoacidosis. Family history of unexplained infant deaths was helpful in reaching the correct diagnosis. In response to therapy, the patient regained consciousness without neurologic deficits and had normal examination. This is, to our knowledge, the first case report of late-onset propionic acidemia that had this presentation and survived.

Novel FBP1 gene mutations in Arab patients with fructose-1,6-bisphosphatase deficiency

Deficiency of fructose-1,6-bisphosphatase (FBP) results in impaired gluconeogenesis, which is characterized by episodes of hyperventilation, apnea, hypoglycemia, and metabolic and lactic acidosis. This autosomal recessive disorder is caused by mutations in the FBP1 gene, which encodes for fructose-1,6-bisphosphatase 1 (FBP1). Although FBP1 gene mutations have been described in FBP-deficient individuals of various ethnicities, there has been limited investigation into the genetics of this disorder in Arab patients. This study employed five consanguineous Arab families, in which 17 patients were clinically diagnosed with FBP deficiency. Seven patients and six carrier parents were analyzed for mutations in the FBP1 gene. DNA sequencing of the FBP1 gene identified two novel mutations in these families. A novel six nucleotide repetitive insertion, c114_119dupCTGCAC, was identified in patients from three families. This mutation encodes for a duplication of two amino acids (p.Cys39_Thr40dup) in the N-terminal domain of FBP1. A novel nonsense c.841G>T mutation encoding for a p.Glu281X truncation in the active site of FBP1 was discovered in patients from two families. The newly identified mutations in the FBP1 gene are predicted to produce FBP1 deficiency. These mutations are the only known genetic causes of FBP deficiency in Arab patients. The p.Cys39_Thr40dup is the first reported amino acid duplication in FBP deficiency patients.

CONCLUSION

This study provides a strong rationale for genetic testing of FBP deficient patients of Arab ethnicity for recurrent or novel mutations in the FBP1 gene.

Insulin-resistant hyperglycaemia complicating neonatal onset of methylmalonic and propionic acidaemias

BACKGROUND

Insulin-resistant hyperglycaemia may occasionally complicate the clinical course of organic acidaemias.

STUDY DESIGN

Clinical observation.

RESULTS

Two term infants, one suffering from acute early-onset methylmalonic acidaemia, the other suffering from acute early-onset propionic acidaemia, presented acutely with dehydration, ketoacidosis, and hyperammonaemia. Urinary organic acid, plasma amino acids, and blood and plasma acylcarnitine analysis allowed the diagnosis of methylmalonic and propionic acidaemias. The detection of the novel c.481G>A (p.Gly161Arg) and the known c.655A>T (p.Asn219Tyr) MUT gene mutations identified the first patient as affected by methylmalonic acidaemia mut type. The high increase of propionylcarnitine after carnitine administration in both patients suggested a greatly elevated metabolic intoxication. Both newborns showed insulin-resistant hyperglycaemia. Patient 1 died, but patient 2, after a strong reduction of glucose administration, survived. To our knowledge, this is the only patient with this complication who survived.

CONCLUSION

Insulin-resistant hyperglycaemia complicating neonatal onset of methylmalonic and propionic acidaemias is probably a marker of a serious disease. One patient with this complication survived after a strong reduction of glucose administration. Even if this is probably only a partial intervention, we hypothesize that in this situation a reduction of glucose administration can reduce almost the risk of persistent hyperglycaemia. Further studies are required to confirm our hypothesis.

Urinary organic metabolite screening of children with influenza-associated encephalopathy for inborn errors of metabolism using GC/MS

BACKGROUND

Influenza-associated encephalopathy (IAE) occurs in childhood often with a serious clinical course and fatal outcomes. We screened children with IAE using GC/MS to determine whether they have metabolic disorders such as organic acidemias.

METHODS

Urine samples from 70 Japanese children with IAE were analyzed between 2001 and 2005 using GC/MS with solvent extraction and direct drying methods.

RESULTS

Apparent metabolic disorders in 6 of 70 tested children included vitamin B12-responsive methylmalonic acidemia (MMA; n=1), fructose-1,6-diphosphatase (FDPase) deficiency (n=1) and non-ketotic dicarboxylic aciduria (n=4) suggesting disorders of fatty acid oxidation. One child had an FDPase deficiency, for which glycerol infusion was contraindicated. Valproic acid metabolites were detected in 10 children and urinary glycerol excretion was increased in 22 of them after glycerol treatment.

DISCUSSION

Our results showed that inborn errors of metabolism (IEM), such as organic acidemias, are detectable among children with IAE. Patients with metabolic disorders such as an FDPase deficiency and MMA often have hypoglycemia, hyperammonemia and acute lactic acidemia. Importantly, a detection of FDPase deficiency in which glycerol infusion is contraindicated suggests careful selection of a treatment strategy for "acute encephalopathy". We detected valproic acid and its metabolites at a rate of 14%, which was considerably higher than that in a control population. Thus, convulsive disorders might be a risk factor associated with IAE.

Isovaleric acidemia: new aspects of genetic and phenotypic heterogeneity

Isovaleric acidemia (IVA) is an autosomal recessive inborn error of leucine metabolism caused by a deficiency of the mitochondrial enzyme isovaleryl-CoA dehydrogenase (IVD) resulting in the accumulation of derivatives of isovaleryl-CoA. It was the first organic acidemia recognized in humans and can cause significant morbidity and mortality. Early diagnosis and treatment with a protein restricted diet and supplementation with carnitine and glycine are effective in promoting normal development in severely affected individuals. Both intra- and interfamilial variability have been recognized. Initially, two phenotypes with either an acute neonatal or a chronic intermittent presentation were described. More recently, a third group of individuals with mild biochemical abnormalities who can be asymptomatic have been identified through newborn screening of blood spots by tandem mass spectrometry. IVD is a flavoenzyme that catalyzes the conversion of isovaleryl-CoA to 3-methylcrotonyl-CoA and transfers electrons to the electron transfer flavoprotein. Human IVD has been purified from tissue and recombinant sources and its biochemical and physical properties have been extensively studied. Molecular analysis of the IVD gene from patients with IVA has allowed characterization of different types of mutations in this gene. One missense mutation, 932C>T (A282V), is particularly common in patients identified through newborn screening with mild metabolite elevations and who have remained asymptomatic to date. This mutation leads to a partially active enzyme with altered catalytic properties; however, its effects on clinical outcome and the necessity of therapy are still unknown. A better understanding of the heterogeneity of this disease and the relevance of genotype/phenotype correlations to clinical management of patients are among the challenges remaining in the study of this disorder in the coming years.

Lactate dehydrogenase activity is inhibited by methylmalonate in vitro

Methylmalonic acidemia (MMAemia) is an inherited metabolic disorder of branched amino acid and odd-chain fatty acid metabolism, involving a defect in the conversion of methylmalonyl-coenzyme A to succinyl-coenzyme A. Systemic and neurological manifestations in this disease are thought to be associated with the accumulation of methylmalonate (MMA) in tissues and biological fluids with consequent impairment of energy metabolism and oxidative stress. In the present work we studied the effect of MMA and two other inhibitors of mitochondrial respiratory chain complex II (malonate and 3-nitropropionate) on the activity of lactate dehydrogenase (LDH) in tissue homogenates from adult rats. MMA potently inhibited LDH-catalyzed conversion of lactate to pyruvate in liver and brain homogenates as well as in a purified bovine heart LDH preparation. LDH was about one order of magnitude less sensitive to inhibition by MMA when catalyzing the conversion of pyruvate to lactate. Kinetic studies on the inhibition of brain LDH indicated that MMA inhibits this enzyme competitively with lactate as a substrate (K (i)=3.02+/-0.59 mM). Malonate and 3-nitropropionate also strongly inhibited LDH-catalyzed conversion of lactate to pyruvate in brain homogenates, while no inhibition was observed by succinate or propionate, when present in concentrations of up to 25 mM. We propose that inhibition of the lactate/pyruvate conversion by MMA contributes to lactate accumulation in blood, metabolic acidemia and inhibition of gluconeogenesis observed in patients with MMAemia. Moreover, the inhibition of LDH in the central nervous system may also impair the lactate shuttle between astrocytes and neurons, compromising neuronal energy metabolism.

Hypoglycemia in association with various organic and amino acid disorders

A number of organic and amino acidemias, particularly those that involve the oxidation of fatty acids, cause hypoglycemia intermittently. This may be associated with distrubances of acid base equilibrium and accumulation of lactic acid and/or ketone bodies. When such diseases are not diagnosed rapidly, they might lead to neurological crippling and, at times, death. As a group, these disorders involve more than 1 organ and their phenotypic expression may include all or a single system. The symptoms may appear soon after birth or as late as 1 year of age. Their early recognition and rapid intervention provide rewarding clinical outcome. With the recent advances in diagnostic techniques, such as the introduction of tandem mass spectrometry (MS), screening for these diseases now can be performed because rapid identification on a large scale is possible. The phenotypes, mutations involved, pathognomonic laboratory findings, prognosis, and treatment procedures available have been reviewed for major diseases.

Neurological dysfunction in methylmalonic acidaemia is probably related to the inhibitory effect of methylmalonate on brain energy production

Methylmalonic acidaemia is an inherited metabolic disorder caused by a severe deficiency of the activity of the enzyme L-methylmalonyl-CoA mutase or its cofactor 5'-deoxyadenosylcobalamin, resulting in tissue accumulation of large quantities of methylmalonic acid. Among the various clinical features, neurological symptoms are frequently observed. Patients may present cerebral atrophy and basal ganglia abnormalities are common. In the present report, we update the current knowledge on the influence of methylmalonic acid on brain metabolism in the hope of better understanding the neurological dysfunction characteristic of methylmalonic acidaemia. We present evidence showing that the metabolite inhibits brain energy production by various mechanisms and propose that a fall in cellular ATP generation leading to excitotoxicity is crucial for the occurrence of the neurological damage observed in these patients.

Unusual presentations of propionic acidemia

The files of 25 patients with propionic acidemia (PA), followed by the Inborn Errors of Metabolism Service (IEMS) at King Faisal Specialist Hospital and Research Centre (KFSH & RC) from 1990 to 1993, were studied retrospectively. In 14 patients PA presented acutely with acidosis, hyperammonemia and thrombocytopenia, while in 11 patients the presentation of the disease was unusual. In the latter group, two neonates with PA initially appeared as a primarily hyperammonemic metabolic disease. In two other neonates the vomiting was so severe that they were diagnosed as intestinal obstruction in referral hospitals. The presentation in three infants was primarily as an immune disorder. In four infants, PA appeared as an acute or chronic encephalopathy, i.e. as a silent organic acidemia, with few other findings of the disease. The clinical picture of PA includes facial and nipple dysmorphia, severe hypotonia and vomiting. Severe thrombocytopenia is the hallmark of the metabolic crisis. In one patient it was noticed late and caused intracranial hemorrhage, while in three others intracranial bleeding caused death. The prognosis in PA remained grave despite rigorous treatment. Only seven of the 25 PA patients remained to have a normal life-style, while eight patients expired. The diagnosis is readily achieved by urine gas chromatography/mass spectrometry (GC/MS), by tandem mass spectrometry (MS/MS), or by enzyme analysis of fibroblasts. While there may be both examiner- and patient-related reasons for the variations in the presentation of PA, one other reason may be the heterogeneity of the molecular defect in propionyl-CoA carboxylase.