Long-term results of selective screening for inborn errors of metabolism

Spectrum of Organic Aciduria Diseases in Tunisia: A 35-year Retrospective Study

Background

Organic aciduria diseases (OADs) occur worldwide, with differences in prevalence and patterns between populations.

Objectives

To describe the spectrum of OADs identified in Tunisia over a 35-years period.

Materials and Methods

This retrospective study included patients who were diagnosed with OADs between 1987 and 2022 in the Laboratory of Biochemistry, Rabta Hospital, Tunisia. Organic acids were analyzed using gas chromatography-mass spectrometry.

Results

A total of 30,670 urine samples were analyzed for OADs, of which 471 were positive for OADs. The estimated incidence of OADs in Tunisia was 6.78 per 100,000 live births. Methylmalonic (n = 146) and propionic (n = 90) acidurias were the most common OADs (estimated incidence: 2.10 and 1.30 per 100,000 live births, respectively). There were 54 cases of L-2-hydroxyglutatric acidurias and 30 cases of pyroglutamic acidurias, which makes it one of the highest in the world. The main clinical features were hypotonia (65%) and feeding difficulties (41%). Age at diagnosis was highly variable, ranging from 1 day to 49 years. Only 27% of the patients were diagnosed within the first month of life. The prevalence of OADs was highest in the Center-East and Southeast regions.

Conclusions

In Tunisia, OADs are relatively frequent, but there are shortcomings regarding the diagnosis of these disorders. The frequency and health/social impact of these disorders warrant the need for implementing newborn screening programs and suitable patient management.

Ex vivo proton spectroscopy (1 H-NMR) analysis of inborn errors of metabolism: Automatic and computer-assisted analyses

There are about 1500 genetic metabolic diseases. A small number of treatable diseases are diagnosed by newborn screening programs, which are continually being developed. However, most diseases can only be diagnosed based on clinical symptoms or metabolic findings. The main biological fluids used are urine, plasma and, in special situations, cerebrospinal fluid. In contrast to commonly used methods such as gas chromatography and high performance liquid chromatography mass spectrometry, ex vivo proton spectroscopy (¹ H-NMR) is not yet used in routine clinical practice, although it has been recommended for more than 30 years. Automatic analysis and improved NMR technology have also expanded the applications used for the diagnosis of inborn errors of metabolism. We provide a mini-overview of typical applications, especially in urine but also in plasma, used to diagnose common but also rare genetic metabolic diseases with ¹ H-NMR. The use of computer-assisted diagnostic suggestions can facilitate interpretation of the profiles. In a proof of principle, to date, 182 reports of 59 different diseases and 500 reports of healthy children are stored. The percentage of correct automatic diagnoses was 74%. Using the same ¹ H-NMR profile-targeted analysis, it is possible to apply an untargeted approach that distinguishes profile differences from healthy individuals. Thus, additional conditions such as lysosomal storage diseases or drug interferences are detectable. Furthermore, because ¹ H-NMR is highly reproducible and can detect a variety of different substance categories, the metabolomic approach is suitable for monitoring patient treatment and revealing additional factors such as nutrition and microbiome metabolism. Besides the progress in analytical techniques, a multiomics approach is most effective to combine metabolomics with, for example, whole exome sequencing, to also diagnose patients with nondetectable metabolic abnormalities in biological fluids. In this mini review we also provide our own data to demonstrate the role of NMR in a multiomics platform in the field of inborn errors of metabolism.

Prevalence of methylmalonic acidemia among newborns and the clinical-suspected population: a meta-analyse

IMPORTANCE

Knowing the scale of rare inborn errors is important for screening and resource allocation. Evidence on the prevalence of methylmalonic acidemia (MMA) among newborns and the clinical-suspected population from large-scale screening programs needs to be systematically synthesized.

OBJECTIVE

To estimate the worldwide prevalence of MMA for newborns and the clinical-suspected population and explore the differences in different regions, periods, and diagnostic technologies.

DATA SOURCES

MEDLINE, Embase, CRD, Cochrane Library, Scopus, CINAHL, and PROSPERO. Study Selection: All studies reporting the epidemiology characteristics of MMA were selected.

DATA EXTRACTION AND SYNTHESIS

Characteristics of study, subjects, and epidemiology were extracted, random-effect models were used for meta-analyses.

MAIN OUTCOME AND MEASURE

Pooled prevalence of MMA.

RESULTS

This study included 111 studies. The pooled prevalence of MMA worldwide was 1.14 per 100,000 newborns (1516/190,229,777 newborns, 95% CI: 0.99-1.29) and 652.11 per 100,000 clinical-suspected patients (1360/4,805,665 clinical-suspected individuals, CI: 544.14-760.07). Asia and Africa got a higher pooled prevalence of MMA. The prevalence of MMA in newborns increased through the years, while that in the clinical-suspected population decreased. Collecting blood ≥ 72 h after birth had a higher pooled prevalence of MMA than collecting during 24 h-72 h after birth. The combining-use of MS/MS and GC/MS had a higher pooled prevalence than the single-use of MS/MS or GC/MS. Prevalence of cbl C, mut, cbl B, cbl A, isolated MMA, combined MMA and homocystinuria, vitamin B12-responsive MMA was synthesized.

CONCLUSIONS AND RELEVANCE

Prevalence of MMA among newborns was extremely low, but considerably high in the clinical-suspected population, indicating the need for more efficient newborn screening strategies and closer monitoring of the high-risk population for the early signs of MMA. Asia and Africa should attach importance to the high prevalence of MMA. Further diagnostic tests were recommended for the combining-use vs single-use of MS/MS and GC/MS and for collecting blood after 72 h vs during 24-72 h after birth.

d-Glycerate kinase deficiency in a neuropediatric patient

d-Glyceric aciduria (DGA) due to d-glycerate kinase deficiency (DGKD) is a rare autosomal-recessive inborn error of metabolism that is usually linked to the metabolism of fructose and serine. We describe a Moroccan patient with DGKD whose metabolic defect has been characterized by metabolite studies, sequencing of genomic DNA and by studies on the RNA level. Since birth the index patient presented with severe muscular hypotonia, joint hypermobility and tremor. Enantioselective analysis showed elevated d-glyceric acid in the urine of the patient, but not in that of his parents. DNA analysis revealed homozygosity in the GLYCTK gene for c.517G>T [p.(Val173Leu)], the first mutation reported for exon 3 of this gene, as well as for the c.530-4A>G polymorphism. RNA studies suggest that none of these sequence variants affects splicing. The mother was heterozygous for both sequence variants, the father heterozygous for the first one and homozygous for the polymorphism, which further supports that c.517G>T is the functionally relevant nucleotide change. The conservation of GLYCTK throughout evolution suggests an important biological role of this enzyme, although it is not known yet how mutations are linked to clinical features. Future studies should investigate the molecular defect in a more general way and search for additional roles of GLYCTK beyond its established role in catabolism of serine and fructose.

The emerging role of the mitochondrial fatty-acid synthase (mtFASII) in the regulation of energy metabolism

Malonyl-CoA synthetase (ACSF3) catalyzes the first step of the mitochondrial fatty acid biosynthesis (mtFASII). Mutations in ACSF3 cause CMAMMA a rare inborn error of metabolism. The clinical phenotype is very heterogeneous, with some patients presenting with neurologic manifestations. In some children, presenting symptoms such as coma, ketoacidosis and hypoglycemia are suggestive of an intermediary metabolic disorder. The overall pathophysiological mechanisms are not understood. In order to study the role of mtFASII in the regulation of energy metabolism we performed a comprehensive metabolic phenotyping with Seahorse technology proteomics in fibroblasts from healthy controls and ACSF3 patients. SILAC-based proteomics and lipidomic analysis were performed to investigate the effects of hypofunctional mtFASII on proteome and lipid homeostasis of complex lipids. Our data clearly confirmed an impaired mitochondrial flexibility characterized by reduced mitochondrial respiration and glycolytic flux due to a lower lipoylation degree. These findings were accompanied by the adaptational upregulation of β-oxidation and by the reduction of anaplerotic amino acids as compensatory mechanism to address the required energy need. Finally, lipidomic analysis demonstrated that the content of the bioactive lipids sphingomyelins and cardiolipins was strongly increased. Our data clearly demonstrate the role of mtFASII in metabolic regulation. Moreover, we show that mtFASII acts as mediator in the lipid-mediated signaling processes in the regulation of energy homeostasis and metabolic flexibility.

Genetic basis of alpha-aminoadipic and alpha-ketoadipic aciduria

Alpha-aminoadipic and alpha-ketoadipic aciduria is an autosomal recessive inborn error of lysine, hydroxylysine, and tryptophan degradation. To date, DHTKD1 mutations have been reported in two alpha-aminoadipic and alpha-ketoadipic aciduria patients. We have now sequenced DHTKD1 in nine patients diagnosed with alpha-aminoadipic and alpha-ketoadipic aciduria as well as one patient with isolated alpha-aminoadipic aciduria, and identified causal mutations in eight. We report nine novel mutations, including three missense mutations, two nonsense mutations, two splice donor mutations, one duplication, and one deletion and insertion. Two missense mutations, one of which was reported before, were observed in the majority of cases. The clinical presentation of this group of patients was inhomogeneous. Our results confirm that alpha-aminoadipic and alpha-ketoadipic aciduria is caused by mutations in DHTKD1, and further establish that DHTKD1 encodes the E1 subunit of the alpha-ketoadipic acid dehydrogenase complex.

[Characterization of inborn errors of intermediary metabolism in mexican patients]

INTRODUCTION

Inborn errors of intermediary metabolism (IEiM) are a group of heterogeneous genetic diseases that are diagnostically challenging and cause significant morbidity and mortality. The aim of this study is to perform a descriptive analysis of the number, type, and clinical features, in a series of cases with IEiM identified through selective diagnosis in a highly specialized pediatric hospital.

MATERIALS AND METHODS

A retrospective study was performed from January of 2000 to December of 2012 by analyzing the files of 204 patients with an IEiM, by selective screening, before and after the implementation of tandem mass spectrometry (MS/MS).

RESULTS

A total of 25 different types of IEiM were found in the 204 files; 102 organic acidurias, 100 aminoacidopathies, and 2 fatty acid oxidation disorders. The introduction of MS/MS increased the number of cases detected by 50%. Patients were referred from 13 different specialists, with pediatricians being the most active. The average interval between onset of symptoms and diagnosis was 18 months.

CONCLUSION

Among the sick Mexican children studied, a wide variety of IEiM was found, propionate defects and maple syrup urine disease being noteworthy. The diagnosis of metabolic disease was delayed in the population studied. These results present evidence to perhaps incorporate IEiM into an expanded newborn screening, or else to perform selective diagnosis in all hospitalized children with suggestive clinical data.

Amino acid disorders detected by quantitative amino acid HPLC analysis in Thailand: an eight-year experience

BACKGROUND

Amino acid disorders are a major group of inborn errors of metabolism (IEM) with variable clinical presentations. This study was aimed to provide the data of amino acid disorders detected in high-risk Thai patients referred to our metabolic lab from all over the country.

METHODS

From 2001 to 2009, we analyzed amino acids by HPLC in 1214 plasma and cerebrospinal fluid specimens. These specimens were obtained from patients with clinical suspicion of IEM or with positive newborn screening. The clinical data of the patients with confirmed diagnoses of amino acid disorders were also analyzed.

RESULTS

Fifty-eight patients were diagnosed with amino acid disorders, including 20 cases (34.5%) with maple syrup urine disease, 13 (22.4%) with phenylketonuria and hyperphenylalaninemia, 13 (22.4%) with nonketotic hyperglycinemia, 9 (15.5%) with urea cycle defects, 2 (3.4%) with classical homocystinuria, and 1 (1.7%) with ornithine aminotransferase deficiency. There was considerable delay in diagnoses which led to poor outcomes in most patients.

CONCLUSION

The prevalence of amino acid disorders in Thailand is distinct from other countries. This will guide the selection of the prevalent IEM for the future expansion of newborn screening program in this country.

Diagnosis of major organic acidurias in children: two years experience at a tertiary care centre

Organic acid disorders are inherited metabolic disorders in which organic acids accumulate in tissues and biological fluids of affected individuals. Classical organic acidurias include methylmalonic aciduria, propionic aciduria, isovaleric aciduria and maple syrup urine disease (MSUD). They are considered the most frequent metabolic disorders among severely ill children. Patients frequently present with acute symptoms early in life. 420 cases clinically suspected to have organic aciduria, with upper age limit of 12 years for a 2-year period (January 2007-December 2008) were enrolled into this study. Metabolic acidosis and neurological symptoms were the most common signs. Screening tests and thin layer chromatography were done for detection of organic acidurias. Identification and quantitation of organic acids in urine and quantification of amino acids in blood were done by high performance liquid chromatography. Out of 420 patients, 45 patients (10.7%) were found to have organic acidurias. 15 cases of methylmalonic aciduria, 16 cases of propionic aciduria, 13 cases of MSUD, and one case of isovaleric aciduria were diagnosed. Results demonstrate the importance of testing for organic acidurias. Since organic aciduria may cause irreversible brain damage if not treated, we recommend selective screening amongst severely ill children despite implied extra costs.

Three Japanese Patients with Beta-Ketothiolase Deficiency Who Share a Mutation, c.431A>C (H144P) in ACAT1 : Subtle Abnormality in Urinary Organic Acid Analysis and Blood Acylcarnitine Analysis Using Tandem Mass Spectrometry

Mitochondrial acetoacetyl-CoA thiolase (T2) deficiency affects both isoleucine catabolism and ketone body metabolism. The disorder is characterized by intermittent ketoacidotic episodes. We report three Japanese patients. One patient (GK69) experienced two ketoacidotic episodes at the age of 9 months and 3 years, and no further episodes until the age of 25 years. She had two uncomplicated pregnancies. GK69 was a compound heterozygote of the c.431A>C (H144P) and c.1168T>C (S390P) mutations in T2 (ACAT1) gene. She was not suspected of having T2 deficiency during her childhood, but she was diagnosed as T2 deficient at the age of 25 years by enzyme assay using fibroblasts. The other two patients were identical twin siblings who presented their first ketoacidotic crisis simultaneously at the age of 3 years 4 months. One of them (GK77b) died during the first crisis and the other (GK77) survived. Even during severe crises, C5-OH and C5:1 were within normal ranges in their blood acylcarnitine profiles and trace amounts of tiglylglycine and small amounts of 2-methyl-3-hydroxybutyrate were detected in their urinary organic acid profiles. They were H144P homozygotes. This H144P mutation has retained the highest residual T2 activity in the transient expression analysis of mutant cDNA thus far, while the S390P mutation did not retain any residual T2 activity. The "mild" H144P mutation may result in subtle profiles in blood acylcarnitine and urinary organic acid analyses. T2-deficient patients with "mild" mutations have severe ketoacidotic crises but their chemical phenotypes may be subtle even during acute crises.

Aminoacylase 1 deficiency associated with autistic behavior

Aminoacylase 1 (ACY1) deficiency is a recently described inborn error of metabolism. Most of the patients reported so far have presented with rather heterogeneous neurologic symptoms. At this moment, it is not clear whether ACY1 deficiency represents a true metabolic disease with a causal relationship between the enzyme defect and the clinical phenotype or merely a biochemical abnormality. Here we present a patient identified in the course of selective screening for inborn errors of metabolism (IEM). The patient was diagnosed with autistic syndrome and admitted to the Children's Memorial Health Institute (CMHI) for metabolic evaluation. Organic acid analysis using gas chromatography-mass spectrometry (GC-MS) revealed increased urinary excretion of several N-acetylated amino acids, including the derivatives of methionine, glutamic acid, alanine, glycine, leucine, isoleucine, and valine. In Epstein-Barr virus (EBV)-transformed lymphoblasts, ACY1 activity was deficient. The mutation analysis showed a homozygous c.1057C>T transition, predicting a p.Arg353Cys substitution. Both parents were heterozygous for the mutation and had normal results in the organic acid analysis using GC-MS. This article reports the findings of an ACY1-deficient patient presenting with autistic features.

Two inborn errors of metabolism in a newborn: glutaric aciduria type I combined with isobutyrylglycinuria

BACKGROUND

Glutaric aciduria type 1 (GA1) is an inborn error in the metabolism of the amino acids tryptophan, lysine and hydroxylysine due to mutations in the GCDH gene coding for glutaryl-CoA dehydrogenase. Affected individuals often suffer from an encephalopathic crisis in infancy or childhood which results in acute striatal injury leading to a severe dystonic-dyskinetic movement disorder. Isobutyryl-coenzyme dehydrogenase (IBD) is an enzyme encoded by the ACAD8 gene and involved in the catabolism of the branched-chain amino acid valine. Both GA1 and IBD deficiency can be detected by expanded newborn screening using tandem-mass spectrometry, if they are considered screening targets.

METHODS

Tandem-mass spectrometry and gas-chromatography with mass-selective detection were used for the assessment of key metabolites in body fluids of a patient with abnormal findings in newborn screening. Mutations were investigated by direct sequencing and by restriction fragment lengths analysis. Valine metabolism was studied in vitro in immortalized lymphocytes.

RESULTS

Following accumulation of acylcarnitines C5DC and C4, of 3-hydroxyglutaric acid and isobutyrylglycine in body fluids, sequence analysis in the GCDH gene revealed homozygosity for a missense mutation in exon 6, c.482G>A, p.Arg161Gln, which had been reported in GA1 before. In the ACAD8 gene a novel mutation c.841+3G>C was identified, which results in loss of exon 7 and predicts a premature stop of translation. Impaired valine degradation was corroborated by the increased post-load level of acylcarnitine C4 in lymphocytes.

CONCLUSION

The molecular basis of two inborn errors of metabolism in a newborn was elucidated. The metabolite studies underline the use of urinary C4 acylcarnitine as a sensitive marker of IBD deficiency. A functional test of IBD activity in lymphocytes may replace more invasive fibroblast studies. In view of the combination of two organic acidurias, which may both affect the level of free carnitine, careful follow-up including regular assessment of the carnitine status of the patient appears prudent.

NMR spectroscopy of aminoacylase 1 deficiency, a novel inborn error of metabolism

Aminoacylase 1 deficiency is a novel inborn error of metabolism. The clinical significance of the deficiency is under discussion, as well as the possible consequences of the defect for brain metabolism and function. This study includes the five originally published cases as well as three novel ones. NMR spectroscopy of urine, serum and cerebrospinal fluid has been used to study these patients. A typical profile with 11 accumulating N-acetylated amino acids was observed in urine from the patients. The concentration of most of the accumulating metabolites is typically 100-500 micromol/mmol creatinine. Two additional minor N-acetylated metabolites remain unidentified. The concentrations of the accumulating metabolites are <20 micromol/L in serum from the patients. Interestingly we found no evidence of an increased concentration of N-acetylated amino acids in the cerebrospinal fluid from one patient. Our data define aminoacylase 1 deficiency at the metabolite level providing a specific urinary profile of accumulating N-acetylated amino acids.

2-Methylbutyryl-coenzyme A dehydrogenase deficiency: functional and molecular studies on a defect in isoleucine catabolism

2-Methylbutyryl-CoA dehydrogenase (MBD; coded by the ACADSB gene) catalyzes the step in isoleucine metabolism that corresponds to the isovaleryl-CoA dehydrogenase reaction in the degradation of leucine. Deficiencies of both enzymes may be detected by expanded neonatal screening with tandem-mass spectrometry due to elevated pentanoylcarnitine (C5 acylcarnitine) in blood, but little information is available on the clinical relevance of MBD deficiency. We biochemically and genetically characterize six individuals with MBD deficiency from four families of different ethnic backgrounds. None of the six individuals showed clinical symptoms attributable to MBD deficiency although the defect in isoleucine catabolism was demonstrated both in vivo and in vitro. Several mutations in the ACADSB gene were identified, including a novel one. MBD deficiency may be a harmless metabolic variant although significant impairment of valproic acid metabolism cannot be excluded and further study is required to assess the long-term outcome of individuals with this condition. The relatively high prevalence of ACADSB gene mutations in control subjects suggests that MBD deficiency may be more common than previously thought but is not detected because of its usually benign nature.

Variations in IBD (ACAD8) in children with elevated C4-carnitine detected by tandem mass spectrometry newborn screening

The isobutyryl-CoA dehydrogenase (IBD) enzyme is involved in the degradation of valine. IBD deficiency was first reported in 1998 and subsequent genetic investigations identified acyl-CoA dehydrogenase (ACAD) 8, now IBD, as the gene responsible for IBD deficiency. Only three individuals homozygous or compound heterozygous for variations in the IBD gene have been reported. We present IBD deficiency in an additional four newborns with elevated C(4)-carnitine identified by tandem mass spectrometry (MS/MS) screening in Denmark and the United States. Three showed urinary excretions of isobutyryl-glycine, and in vitro probe analysis of fibroblasts from two newborns indicated enzymatic IBD defect. Molecular genetic analysis revealed seven new rare variations in the IBD gene (c.348C>A, c.400G>T, c.409G>A, c.455T>C, c.958G>A, c.1000C>T and c.1154G>A). Furthermore, sequence analysis of the short-chain acyl-CoA dehydrogenase (SCAD) gene revealed heterozygosity for the prevalent c.625G>A susceptibility variation in all newborns and in the first reported IBD patient. Functional studies in isolated mitochondria demonstrated that the IBD variations present in the Danish newborn (c.409G>A and c.958G>A) together with a previously published IBD variation (c.905G>A) disturbed protein folding and reduced the levels of correctly folded IBD tetramers. Accordingly, low/no IBD residual enzyme activity was detectable when the variant IBD proteins were overexpressed in Chang cells.

Mutations in ACY1, the gene encoding aminoacylase 1, cause a novel inborn error of metabolism

N-terminal acetylation of proteins is a widespread and highly conserved process. Aminoacylase 1 (ACY1; EC 3.5.14) is the most abundant of the aminoacylases, a class of enzymes involved in hydrolysis of N-acetylated proteins. Here, we present four children with genetic deficiency of ACY1. They were identified through organic acid analyses using gas chromatography-mass spectrometry, revealing increased urinary excretion of several N-acetylated amino acids, including the derivatives of methionine, glutamic acid, alanine, leucine, glycine, valine, and isoleucine. Nuclear magnetic resonance spectroscopy analysis of urine samples detected a distinct pattern of N-acetylated metabolites, consistent with ACY1 dysfunction. Functional analyses of patients' lymphoblasts demonstrated ACY1 deficiency. Mutation analysis uncovered recessive loss-of-function or missense ACY1 mutations in all four individuals affected. We conclude that ACY1 mutations in these children led to functional ACY1 deficiency and excretion of N-acetylated amino acids. Questions remain, however, as to the clinical significance of ACY1 deficiency. The ACY1-deficient individuals were ascertained through urine metabolic screening because of unspecific psychomotor delay (one subject), psychomotor delay with atrophy of the vermis and syringomyelia (one subject), marked muscular hypotonia (one subject), and follow-up for early treated biotinidase deficiency and normal clinical findings (one subject). Because ACY1 is evolutionarily conserved in fish, frog, mouse, and human and is expressed in the central nervous system (CNS) in human, a role in CNS function or development is conceivable but has yet to be demonstrated. Thus, at this point, we cannot state whether ACY1 deficiency has pathogenic significance with pleiotropic clinical expression or is simply a biochemical variant. Awareness of this new genetic entity may help both in delineating its clinical significance and in avoiding erroneous diagnoses.

Quantitative acylcarnitine profiling in peripheral blood mononuclear cells using in vitro loading with palmitic and 2-oxoadipic acids: biochemical confirmation of fatty acid oxidation and organic acid disorders

Organic acid (OAD) and fatty acid oxidation disorders (FAOD) are inborn errors of metabolism often presenting with life-threatening metabolic decompensation followed by (irreversible) organ failure, and even death during catabolic state. Most of these diseases are considered as treatable, and metabolic decompensations can be avoided by early diagnosis and start of therapy. Confirmation of suspected diagnosis currently relies on enzymatic and mutation analyses and in vitro loading of palmitic acid in human skin fibroblast cultures. Furthermore, in some cases potentially life-threatening in vivo loading or fasting tests are still performed. In this study, we established a standardized in vitro loading test in peripheral blood mononuclear cells (PBMC) that allows reliable biochemical confirmation of a suspected diagnosis within 1 week. Patients with confirmed diagnosis of short-, medium-, very-long-chain, and long-chain 3-hydroxyacyl-CoA dehydrogenase deficiencies, methylmalonic, propionic, isovaleric acidurias, and glutaric aciduria type I were included in the study. PBMC, isolated from heparinized venous blood samples of these individuals were incubated for 5 days with palmitic acid or 2-oxoadipic acid (glutaric aciduria type I), respectively, and quantitative acylcarnitine profiling was subsequently performed in supernatants using electrospray ionization tandem mass spectrometry. All patients were clearly identified, including those with mild biochemical phenotypes who, in particular, are at risk to be missed under balanced metabolic conditions. In glutaric aciduria type I, the same results were also obtained using lymphoblasts. In conclusion, our assay allows biochemical confirmation of a number of FAOD and OAD and could easily be implemented into the confirmatory diagnostic work-up.

Isobutyryl-CoA dehydrogenase deficiency: isobutyrylglycinuria and ACAD8 gene mutations in two infants

Isobutyryl-CoA dehydrogenase (IBD) is an enzyme involved in the catabolism of the branched-chain amino acid valine. We report a third and a fourth child with IBD deficiency who were both detected during newborn screening with tandem mass spectrometry and so far do not receive any treatment. The diagnosis was confirmed by biochemical and molecular studies. One of the children is homozygous for the mutation M128I in the ACAD8 gene, which is predicted to affect the substrate binding cavity. The other child is compound heterozygous for a frameshift mutation F33fsins and a missense mutation V203I. It is as yet uncertain whether IBD deficiency may cause significant morbidity in affected children and whether treatment is necessary. In view of the limited experience worldwide, careful monitoring of the children is recommended.

Detection of organic acidemias in Brazil

BACKGROUND

Organic acidurias or organic acidemias are inherited metabolic disorders in which organic acids (carboxylic acids) accumulate in tissues and physiologic fluids of affected individuals. They are considered the most frequent metabolic disorders among severely ill children. Patients frequently present acute symptoms in early life. Metabolic acidosis and neurologic symptoms are the most common signs.

METHODS

Urine specimens obtained from 1,926 children from January 1994 to July 2001 were used in analyses. Venous blood specimens were also collected from some patients. Samples were initially submitted to screening tests for detection of inborn errors of metabolism. Identification and semi-quantitation of organic acids in urine were performed by gas chromatography or gas chromatography coupled to mass spectrometry using capillary column (DB-5) and flame ionization detection.

RESULTS

Ninety three (4.8%) cases of organic acidemias were diagnosed among 1,926 patients investigated from January 1994 to July 2001. Prompt therapy was instituted after diagnosis in a considerable number of patients and resulted in rapid improvement in their symptomatology, distinct from our previous cases diagnosed abroad where patients representing index cases died before any measure could be taken.

CONCLUSIONS

Results demonstrate the importance of diagnosing organic acidurias in loco in developing countries despite implied extra costs.

Isolated biotin-resistant 3-methylcrotonyl-CoA carboxylase deficiency: long-term outcome in a case with neonatal onset

A patient with early-onset 3-methylcrotonyl coenzyme A carboxylase (MCC) deficiency showing a severe clinical course is described. Abnormal eye and head movements suggestive of seizures were noticed soon after birth. Tonic convulsions at the age of 10 weeks led to admission. Urinary organic acid analysis using gas chromatography-mass spectrometry at 3 months of age revealed elevated concentrations of 3-hydroxyisovaleric acid (3HIVA) and 3-methylcrotonylglycine but normal levels of lactate, 3-hydroxypropionate and methylcitrate suggesting isolated MCC deficiency. This was confirmed by enzyme assays in lymphocytes and cultured skin fibroblasts: MCC activity was virtually undetectable whereas activities of propionyl-CoA and pyruvate carboxylases were within the normal range. A low protein (0.8-1.5 g/kg/day) diet supplemented with a leucine-free amino acid mixture resulted in a marked decrease of 3HIVA excretion. L-Carnitine and biotin administration had no effect on the clinical condition or metabolite excretion. Supplementation with glycine resulted in only a temporary fall of 3HIVA excretion and was therefore discontinued. L-Carnitine therapy was reintroduced later because of secondary carnitine deficiency. Compliance with treatment was poor until the age of 27 months resulting in a severe episode with seizures and coma. The general clinical condition of the patient was always good but his psychomotor development was delayed and seizures were not continuously under good control due to poor therapy compliance. The boy is now 10.5 years old and attending a school for children with learning handicaps.

CONCLUSION

Isolated MCC deficiency of early-onset is a rare condition exhibiting a more severe clinical course than the later-onset form described in most other cases. The prognostic value of 3 HIVA measurements in CSF and serum should be evaluated in future cases.

Seizures in a boy with succinic semialdehyde dehydrogenase deficiency treated with vigabatrin (gamma-vinyl-GABA)

Succinic semialdehyde dehydrogenase (SSADH) deficiency is an autosomal recessive disease involving the catabolism of the neurotransmitter gamma-aminobutyric acid (GABA). The main symptoms include retardation of psychomotor and language development, muscle hypotonia and non-progressive ataxia. Therapy consisting of approximately 75 mg/kg per day of vigabatrin, an irreversible inhibitor of GABA-transaminase, is reported to lead to some improvement of the clinical condition in affected patients. We report on a 12-year-old boy with SSADH deficiency who, when treated with 75 mg/kg per day of vigabatrin, showed marked amelioration of symptoms but also EEG changes and two generalized seizures. On discontinuing vigabatrin therapy, the seizures resolved and the EEG improved, but the patient's clinical condition deteriorated to its pre-treatment state. A stable EEG without the recurrence of seizures as well as renewed improvement of cognitive and behavioural functions was achieved with a reduced vigabatrin dose of 25 mg/kg per day. We conclude that vigabatrin in SSADH deficiency should be administered in a gradually increasing dosage combined with frequent evaluation of the clinical condition and the EEG.

Selective screening for inborn errors of metabolism--past, present and future

Selective screening for hereditary metabolic disorders has developed from a highly specialized activity, provided mostly by research oriented scientists, to an important diagnostic tool in the work-up of paediatric patients. A brief overview is given of the present status of selective screening in Europe, the USA and Israel including the distribution of centres and resources for diagnosis, therapy and follow-up. Current status and most pressing problems vary widely between different countries. Most countries still lack an organized network of clinical genetic centres which are capable of competent and comprehensive diagnostic and therapeutic services. For example, it must be assumed that more than 60% of patients with inherited metabolic diseases, which could be diagnosed nowadays, remain un(mis)diagnosed in former Western Germany. Early diagnosis and treatment are important determinants for a successful approach towards inherited metabolic diseases. Therefore, screening and therapy for inborn errors of metabolism has to be organized in clinical genetic centres, each serving a population between 2 and 4 million. The quality of the services provided depends on good pre- and postgraduate training of physicians (paediatricians) in the field of metabolic diseases, good co-operation between the referring physician and the clinical genetic centre and a broad spectrum of highly specialized metabolic investigations in the respective centre. The institutionalization has to include licensing of laboratories, directors and personnel, as well as quality control and proficiency testing. The size of the centres cannot be judged on the basis of the work involved with selective screening for inborn errors of metabolism alone.(ABSTRACT TRUNCATED AT 250 WORDS)