Biomedical subjects

Georg F Hoffmann

Publications and source records attributed to Georg F Hoffmann.

At least 19 recordsLinked to original sources

PubMed2004

Frequencies of inherited organic acidurias and disorders of mitochondrial fatty acid transport and oxidation in Germany.

UNLABELLED: The lack of epidemiological data on the frequency and/or burden of organic acidurias (OA) and mitochondrial fatty acid transport and oxidation disorders (mtFATOD) is one reason for hesitation to expand newborn screening (NBS) by tandem mass spectrometry (MS-MS). From 1999 to 2000, the frequency of ten potentially treatable OA and mtFATOD was assessed by active nation-wide surveillance on cases presenting with clinical symptoms using the German Paediatric Surveillance Unit (ESPED) system. Case ascertainment was complemented by a second independent source: 3-monthly inquiries in the metabolic laboratories performing secondary selected screening for OA and mtFATOD. Frequency estimates for clinically symptomatic cases older than 7 days in a birth cohort of 844,575 conventionally screened children was compared to the frequency found in a cohort of 382,247 screened by MS-MS in Bavaria and Baden-Württemberg. The overall frequency of the ten conditions considered was 1:8,000 (95% CI 1:11,000-1:6,000) by MS-MS as compared to 1:23,000 (95% CI 1:36,000-1:17,000) in symptomatic cases presenting mainly with metabolic crisis. The contributions of medium-chain acyl-CoA dehydrogenase deficiency (MCADD), other mtFATOD and OA were 29, 4 and 13 among the 46 cases identified by MS-MS, and 19, 1 and 13 among the 33 clinically symptomatic cases, respectively. Acute metabolic crisis, with a lethal outcome in four patients, was reported for 22/33 clinically symptomatic cases. No clinically symptomatic cases were reported from cohorts with screened by MS-MS. CONCLUSION: ten potentially treatable organic acidurias and mitochondrial fatty acid transport and oxidations disorders were more common than phenylketonuria with organic acidurias accounting for 28% of the cases detected by newborn screening and 39% of the cases identified on high risk screening. These conditions were related to considerable morbidity and mortality. Considerations for their inclusion in expanded newborn screening programmes might be warranted.

Acyl-CoA Dehydrogenase↗

PubMed2004

Pathomechanisms of neurodegeneration in glutaryl-CoA dehydrogenase deficiency.

Glutaryl-CoA dehydrogenase deficiency is an inherited organic aciduria with predominantly neurological presentation. Biochemically, it is characterized by an accumulation and enhanced urinary excretion of two key organic acids, glutaric acid and 3-hydroxyglutaric acid. If untreated, acute striatal degeneration is often precipitated by febrile illnesses during a vulnerable period of brain development in infancy or early childhood, resulting in a dystonic dyskinetic movement disorder. The mechanism underlying these acute encephalopathic crises has been partially elucidated using in vitro and in vivo models. 3-Hydroxyglutaric and glutaric acids share structural similarities with the main excitatory amino acid glutamate and are considered to play an important role in the pathophysiology of this disease. 3-Hydroxyglutaric acid induces excitotoxic cell damage specifically via activation of N-methyl-D-aspartate receptors. Furthermore, glutaric and 3-hydroxyglutaric acids indirectly modulate glutamatergic and GABAergic neurotransmission, resulting in an imbalance of excitatory and inhibitory neurotransmission. It also has been suggested that secondary amplification loops potentiate the neurotoxic properties of these organic acids. Probable mechanisms for this effect include cytokine-stimulated nitric oxide production, a decrease in energy metabolism, and reduction of cellular creatine phosphate levels. Finally, maturation-dependent changes in the expression of neuronal glutamate receptors may affect the vulnerability to 3-hydroxyglutaric and glutaric acid toxicity.

Amino Acid Metabolism, Inborn Errors↗

PubMed2003

Beta-carotene cleavage products after oxidation mediated by hypochlorous acid--a model for neutrophil-derived degradation.

After beta-carotene failed in certain clinical efficacy trials, there is evidence that the carotenoid might even be harmful, especially to smokers, when given in high dosages. These negative effects might be mediated in part also by carotenoid cleavage products (CPs) having a high reactivity towards biomolecules. The authors postulate that in certain tissues oxidative, nonenzymatic cleavage of carotenoids is carried out primarily by oxidants liberated by polymorphonuclear leukocytes (PML). In this study, we show that beta-carotene is degraded by stimulated PML in vitro. This gives the pathophysiological meaning to our further experiments in which beta-carotene degradation by hypochlorous acid and consecutive CP formation were investigated. While formation of apo-carotenals under these conditions has been studied before, this was not the case for short chain products. Performing gas chromatography mass spectrometry, we were able to identify for the first time 5,6-epoxi-beta-ionone, ionene, beta-cyclocitral, beta-ionone, dihydroactinidiolide, and 4-oxo-beta-ionone as CPs formed after degradation of beta-carotene mediated by hypochlorous acid. Our findings may be of biological relevance because beta-carotene CPs are highly reactive and, therefore, potentially toxic.

Chromatography, High Pressure Liquid↗

PubMed2003

eIF2B-related disorders: antenatal onset and involvement of multiple organs.

Leukoencephalopathy with vanishing white matter, also called "childhood ataxia with central nervous system hypomyelination," is the first human disease related to mutations in any of the five genes encoding subunits of eukaryotic initiation factor eIF2B or any translation factor at all. eIF2B is essential in all cells of the body for protein synthesis and the regulation of this protein synthesis under different stress conditions. It is surprising that mutations in the eIF2B genes have been reported to lead to abnormalities of the white matter of the brain only, although it has been shown recently that ovarian failure may accompany the leukoencephalopathy. Another surprising observation is that the onset of the disease varies from early childhood to adulthood, with the exception of Cree leukoencephalopathy, a disease related to a particular mutation in one of the eIF2B genes, which invariably has its onset within the first year of life. We analyzed the eIF2B genes of nine patients with an antenatal- or early-infantile-onset encephalopathy and an early demise and found mutations in eight of the patients. In addition to signs of a serious encephalopathy, we found oligohydramnios, intrauterine growth retardation, cataracts, pancreatitis, hepatosplenomegaly, hypoplasia of the kidneys, and ovarian dysgenesis. Until now, no evidence had been found for a genotype-phenotype correlation, but the consistently severe phenotype in affected siblings among our patients and in Cree encephalopathy patients suggests an influence of the genotype on the phenotype.

Abnormalities, Multiple↗

PubMed2003

Methylmalonic acid, a biochemical hallmark of methylmalonic acidurias but no inhibitor of mitochondrial respiratory chain.

Methylmalonic acidurias are biochemically characterized by an accumulation of methylmalonic acid and alternative metabolites. An impairment of energy metabolism plays a key role in the pathophysiology of this disease, resulting in neurodegeneration of the basal ganglia and renal failure. It has become the subject of intense debates whether methylmalonic acid is the major toxin, inhibiting respiratory chain complex II. To elucidate whether methylmalonic acid is a respiratory chain inhibitor, we used spectrophotometric analysis of complex II activity in submitochondrial particles from bovine heart, radiometric analysis of 14C-labeled substrates (pyruvate, malate, succinate), and analysis of ATP production in muscle from mice. Methylmalonic acid revealed no direct effects on the respiratory chain function, i.e. on single electron transferring complexes I-IV, ATPase, and mitochondrial transporters. However, we identified a variety of variables that must be carefully controlled to avoid an artificial inhibition of complex II activity. In summary, the study verifies our hypothesis that methylmalonic acid is not the major toxic metabolite in methylmalonic acidurias. Inhibition of respiratory chain and tricarboxylic acid cycle is most likely induced by synergistically acting alternative metabolites, in particular 2-methylcitric acid, malonic acid, and propionyl-CoA.

Acyl Coenzyme A↗

PubMed2003

Lack of creatine in muscle and brain in an adult with GAMT deficiency.

Guanidinoacetate methyltransferase deficiency, which so far has been exclusively detected in children, was diagnosed in a 26-year-old man. The full-blown spectrum of clinical symptoms already had been present since infancy without progression of symptoms during adolescence. Cranial magnetic resonance imaging showed normal findings. Ophthalmological examination showed no retinal changes. Besides creatine deficiency in the brain, a distinct lack of phosphocreatine in skeletal muscle was proved by (31)P magnetic resonance spectroscopy. Creatine substitution combined with a guanidinoacetate-lowering diet introduced first at the age of 26 years was shown to be effective by an impressive improvement of epileptic seizures, mental capabilities, and general behavior and by normalization of the (31)P spectrum in the skeletal muscle.

Adult↗

PubMed2003

Approach to the diagnosis of neurotransmitter diseases exemplified by the differential diagnosis of childhood-onset dystonia.

We present our approach to the diagnosis of pediatric neurotransmitter diseases exemplified by the differential diagnosis of children presenting with dystonia. This approach is based upon the primary aim of early diagnosis of treatable conditions and the need for a logical series of investigations. We have tried to be comprehensive with our coverage but are aware that "new" pediatric neurotransmitter diseases continue to be delineated and that, similarly, a proportion of children presenting with dystonia remain undiagnosed. If this is the case, all of the investigations suggested here may need to be performed regardless of age and presentation. However, of more value is a careful clinical reevaluation.

Child↗

PubMed2003

Tyrosine hydroxylase deficiency causes progressive encephalopathy and dopa-nonresponsive dystonia.

Tyrosine hydroxylase (TH) is the key enzyme in the biosynthesis of the catecholamines dopamine, epinephrine, and norepinephrine. Recessively inherited deficiency of TH was recently identified and incorporated into recent concepts of genetic dystonias as the cause of recessive Dopa-responsive dystonia or Segawa's syndrome in analogy to dominantly inherited GTP cyclohydrolase I deficiency. We report four patients with TH deficiency and two with GTP cyclohydrolase I deficiency. Patients with TH deficiency suffer from progressive infantile encephalopathy dominated by motor retardation similar to a primary neuromuscular disorder, fluctuating extrapyramidal, and ocular and vegetative symptoms. Intellectual functions are mostly compromised. Prenatally disturbed brain development and postnatal growth failure were observed. Treatment with levodopa ameliorates but usually does not normalize symptoms. Compared with patients with dominantly inherited GTP cyclohydrolase I deficiency, catecholaminergic neurotransmission is severely and constantly impaired in TH deficiency. In most patients, this results not in predominating dystonia, a largely nondegenerative condition, but in a progressive often lethal neurometabolic disorder, which can be improved but not cured by L-dopa. Investigations of neurotransmitter defects by specific cerebrospinal fluid determinations should be included in the diagnostic evaluation of children with progressive infantile encephalopathy.

Amino Acid Metabolism, Inborn Errors↗

PubMed2003

Mutations in the AUH gene cause 3-methylglutaconic aciduria type I.

The conversion of 3-methylglutaconyl-CoA to 3-hydroxy-3-methylglutaryl-CoA is the only step in leucine catametabolism yet to be characterized at enzyme and DNA levels. The deficiency of the putative mitochondrial enzyme 3-methylglutaconyl-CoA hydratase associates with the rare organic aciduria 3-methylglutaconic aciduria type I (MGA1), but neither the enzyme nor its gene have been described in any organism. Here we report that human 3-methylglutaconyl-CoA hydratase is identical with a previously described RNA-binding protein (designated AUH) possessing enoyl-CoA hydratase activity. Molecular analyses in five patients from four independent families revealed homozygosity or compound heterozygosity for mutations in the AUH gene; most mutations are predicted to completely abolish protein function. Mutations identified include c.80delG, R197X, IVS8-1G>A, A240V, and c.613_614insA. Clinical severity of MGA1 in published patients has been quite variable. Included in the present study is an additional patient with MGA1 who was detected by neonatal screening and has remained asymptomatic up to his present age of 2 years. The boy is homozygous for an N-terminal frameshift mutation in the AUH gene. Complete absence of 3-methylglutaconyl-CoA hydratase/AUH appears to be compatible with normal development in some cases. Further work is required to identify external or genetic factors associated with development of clinical problems in patients with MGA1.

Amino Acid Metabolism, Inborn Errors↗

PubMed2003

The molecular basis of phenylalanine hydroxylase deficiency in Croatia.

We present the results of a comprehensive analysis of mutations, polymorphisms and haplotypes in the phenylalanine hydroxylase (PAH) gene in 39 Croatian families with phenylketonuria (PKU). A total of 21 disease-causing mutations was identified on 78 out of 79 independent chromosomes. The commonest mutation, R408W on haplotype 2 was found with a relative frequency of 37 %. P281L accounted for 11 %, R261Q and E390G each for 9 % of mutant chromosomes. There were three novel mutations: L249P (c.746T>C) in exon 7, IVS8+2T>C (c.912T>C) in intron 8, and F402L (c.1206T>G) in exon 12 of the PAH gene. Two known PKU mutations were found in cis on the same chromosome in one family, highlighting the need to perform full mutation scanning in recessive disease genes for molecular diagnosis even if two known mutations have been identified in a patient. This is the first comprehensive report on PKU mutations in southeastern Europe, adding to the growing bulk of molecular data for population genetic investigations.

Croatia↗

PubMed2003

Accurate measurement of free carnitine in dried blood spots by isotope-dilution electrospray tandem mass spectrometry without butylation.

BACKGROUND: To test the feasibility of free carnitine (FC) determination in dried blood spot specimens (DBS) by stable isotope-dilution electrospray-ionisation tandem mass spectrometry (MS/MS). METHODS: The MS/MS method established for newborn screening, measuring acylcarnitines by positive precursor ion scan of m/z 85 in DBS, was adapted by omitting the butylation and heating step during sample preparation. FC measurement in DBS by this non-butylating MS/MS assay was compared with the butylating MS/MS method and the spectrophotometric Cobas method. RESULTS: FC measurement by the non-butylating MS/MS method meets the demands for a bioanalytical microassay with respect to linearity, detection limit (LOD), accuracy, and precision. Formation of FC was 0-1% and 1-4% in liquid samples and in DBS by the non-butylating MS/MS method, while 3-10% and 8-16% by the butylating method, respectively. Acid-catalysed hydrolysis (butanolysis) in liquid samples was higher for short-chain acylcarnitines (acetyl- and propionylcarnitine). Hydrolysis in DBS was more pronounced for long-chain acylcarnitines. FC concentrations in healthy newborns without butylation were 35% lower than those measured by the established newborn screening assay. CONCLUSIONS: The non-butylating MS/MS assay provides a simple and accurate method for FC determination in DBS and represents a trivial but important adaptation of a method already used in many laboratories.

Calibration↗

PubMed2003

Cytosine arabinofuranoside-induced activation of astrocytes increases the susceptibility of neurons to glutamate due to the release of soluble factors.

Activation of astrocytes occurs during many forms of CNS injury, but its importance for neuronal survival is poorly understood. When hippocampal cultures of neurons and astrocytes were treated from day 2-4 in vitro (DIV 2-4) with 1 microM cytosine arabinofuranoside (AraC), we observed a stellation of astrocytes, an increase in glial fibrillary acidic protein (GFAP) level as well as a higher susceptibility of the neurons to glutamate compared with cultures treated from DIV 2-4 with vehicle. To find out whether factors released into the culture medium were responsible for the observed differences in glutamate neurotoxicity, conditioned medium of AraC-treated cultures (MCMAraC) was added to vehicle-treated cultures and conditioned medium of vehicle-treated cultures (MCMvh) was added to AraC-treated cultures 2 h before and up to 18 h after the exposure to 1mM glutamate for 1 h. MCMAraC increased glutamate neurotoxicity in vehicle-treated cultures and MCMvh reduced glutamate neurotoxicity in AraC-treated cultures. Heat-inactivation of MCMvh increased, whereas heat-inactivation of MCMAraC did not affect glutamate toxicity suggesting that heat-inactivation changed the proportion of factors in MCMvh inhibiting and exacerbating the excitotoxic injury. Similar findings were obtained using conditioned medium of pure astrocyte cultures of DIV 12 treated from DIV 2-4 with vehicle or 1 microM AraC suggesting that heat-sensitive factors in MCMvh were mainly derived from astrocytes. Treatment of hippocampal cultures with 1mM dibutyryl-cAMP for 3 days induced an activation of the astrocytes similar to AraC and increased neuronal susceptibility to glutamate. Our findings provide evidence that activation of astrocytes impairs their ability to protect neurons after excitotoxic injury due to changes in the release of soluble and heat-sensitive factors.

Animals↗

PubMed2003

Mevalonate kinase deficiency: enlarging the clinical and biochemical spectrum.

OBJECTIVE: Mevalonic aciduria as a result of mevalonate kinase deficiency is an inborn error of cholesterol biosynthesis characterized by dysmorphology, psychomotor retardation, progressive cerebellar ataxia, and recurrent febrile crises, usually manifesting in early infancy, accompanied by hepatosplenomegaly, lymphadenopathy, arthralgia, and skin rash. The febrile crises are similar to those observed in hyperimmunoglobulinemia D and periodic fever syndrome (HIDS). Pathogenic mutations in the mevalonate kinase gene in both disorders have demonstrated a common genetic basis. Our aim was to describe the clinical picture of adolescent patients with mevalonate kinase deficiency and to expand the clinical and biochemical spectrum of mevalonate kinase deficiency, particularly with regard to HIDS. METHODS: We report the clinical history and biochemical findings of 3 patients with mevalonic aciduria. RESULTS: In 2 siblings with mevalonic aciduria, a 15-year-old girl and a 14-year-old boy, the phenotype shifted with age. Ataxia has become the predominant clinical manifestation, whereas the febrile attacks occur less frequently but as yet have not disappeared. Both of them show marked elevations of immunoglobulin D (IgD). Psychomotor development is retarded but not regressive. Short stature developed in both patients. Additional findings include the development of retinal dystrophy and cataracts in both of them. The third patient is a 6-year-old boy who presented at the age of 5 years with cerebellar ataxia and retinal dystrophy. He is different from all known patients with mevalonic aciduria because of the mild neurologic involvement and because he has never developed febrile crises. In addition, levels of IgD were repeatedly normal. CONCLUSION: The clinical and biochemical spectrum of patients with mevalonic aciduria is heterogeneous. Manifestations of the disease seem to be age dependent, as evident from this first report of adolescent patients. In patients who survive infancy, short stature, ataxia caused by cerebellar atrophy, and ocular involvement with retinal dystrophy become predominant findings. Recurrent febrile crises seem to diminish with increasing age and may not even be an obligatory finding. Elevation of IgD is most likely a secondary phenomenon that seems to be linked to recurrent febrile crises.

Adolescent↗

PubMed2003

Expanded newborn screening for inborn errors of metabolism by electrospray ionization-tandem mass spectrometry: results, outcome, and implications.

OBJECTIVE: The aims of this study were to determine the impact of expanded newborn screening using tandem mass spectrometry (MS/MS) on the overall detection rate of inborn errors of metabolism in Germany and to assess the outcome for the patients that were diagnosed. METHODS: During the period of study, 250,000 neonates in a German population were investigated for 23 inborn errors of metabolism by electrospray ionization-MS/MS. The overall value of the screening program was estimated by 1) complete ascertainment of all positive tests; 2) definite assignment of all diagnoses including reconfirmation at 12 months; and 3) clinical follow-up of all detected patients in an overall interval of 42 months. The mean observation period was 13.5 months per child. RESULTS: In 106 newborns, confirmed inborn errors of metabolism were found. The disorders were classified as 50 classic forms and 56 variants. A total of 825 tests (0.33%) were false-positives. Seventy of the 106 newborns with confirmed disorders were judged to require treatment. Six children developed symptoms despite treatment. Three children had died. Among 9 children who became symptomatic before report of the results of screening, in 6 the diagnosis had been made in advance of the screening report. In evaluation of the screening program, 61 of the 106 identified children (58% of true-positives, or 1 of 4100 healthy newborns) were judged to have benefited from screening and treatment, because the diagnosis had not been made before screening. None of these infants had died and none developed psychomotor retardation or metabolic crisis during the follow-up period. CONCLUSIONS: The screening by MS/MS for up to 23 additional disorders has approximately doubled the detection rate compared with that achieved by the conventional methods used in Germany. This strategy represents valuable preventive medicine by enabling diagnosis and treatment before the onset of symptoms.

Acyl-CoA Dehydrogenase↗

PubMed2002

A method for quantitative acylcarnitine profiling in human skin fibroblasts using unlabelled palmitic acid: diagnosis of fatty acid oxidation disorders and differentiation between biochemical phenotypes of MCAD deficiency.

Inherited disorders of fatty acid oxidation are a group of acute life-threatening but treatable disorders, clinically complicated by severe hypoketotic hypoglycemia precipitated by prolonged fasting. Among them, medium-chain acyl-CoA dehydrogenase (MCAD) deficiency is by far the most frequent disorder. Here we report a modified method for quantitative acylcarnitine profiling by electrospray ionisation-tandem mass spectrometry (ESI-MS-MS) in human skin fibroblasts using unlabelled palmitic acid as substrate. The reliability of this method was tested in cultured skin fibroblasts from previously diagnosed patients with specific carnitine cycle and fatty acid beta-oxidation defects. Furthermore, acylcarnitine profiling was investigated in fibroblasts and dried blood spots from patients with different variants of MCAD deficiency. ESI-MS-MS-based investigation of cultured skin fibroblasts from patients with disorders of fatty acid oxidation revealed a pathognomonic acylcarnitine profiling. In addition, this method delineated different variants of MCAD deficiency, i.e. mild and classical. The octanoylcarnitine (C8)-to-decanoylcarnitine (C10) and C8-to-acetylcarnitine (C2) ratios were the most specific markers to differentiate mild and classical forms of MCAD deficiency in fibroblasts. Similar results were obtained by quantitative acylcarnitine profiling in dried blood spots. In conclusion, this novel technique is a powerful tool for the investigation of fatty acid oxidation disorders under standardized conditions in fibroblasts.

Acyl-CoA Dehydrogenase↗

PubMed2002

Chronic treatment with glutaric acid induces partial tolerance to excitotoxicity in neuronal cultures from chick embryo telencephalons.

Glutaryl-CoA dehydrogenase deficiency (GDD) is characterized biochemically by an accumulation of glutaric (GA) and 3-hydroxyglutaric (3-OH-GA) acids and clinically by the development of acute striatal degeneration. 3-OH-GA was recently shown to induce neuronal damage via N-methyl-D-aspartate (NMDA) receptors. The pathogenetic role of GA, however, remains unclear. We demonstrate that GA exerts a dual action in cultured chick embryo neurons. Short-term incubation with millimolar concentrations of GA induces a weak neuronal damage, adding to 3-OH-GA neurotoxicity. In contrast, chronic treatment with subtoxic, micromolar concentrations of GA results in partial tolerance to 3-OH-GA- and NMDA-induced cell damage. A downregulation of NMDA receptors, in particular of the NR2B subunit, is critically involved in this GA-induced effect, resulting in a reduced Ca(2+) increase and generation of reactive oxygen species after acute exposure to NMDA or 3-OH-GA. Furthermore, GA decreases Na(+)/K(+)-ATPase activity, which is prevented by glutathione, suggesting a modulation of NMDA receptor function via resting membrane potential and Na(+)-dependent glutamate transport. In contrast, GA does not inhibit mitochondrial respiratory chain and beta-oxidation of fatty acids, virtually excluding an activation of NMDA receptors secondary to ATP depletion. These results strongly suggest that GA modulates the NMDA receptor-mediated neurotoxicity of 3-OH-GA, providing an explanatory basis for the non-linear relationship between organic acid concentrations and disease progression in GDD patients. Furthermore, GA-induced downregulation of NMDA receptors might be involved in the delayed cerebral maturation of GDD patients, resulting in frontotemporal atrophy and a reduced opercularization, which are common neuroradiological findings in GDD patients.

Animals↗

PubMed2002

Neurodegeneration in methylmalonic aciduria involves inhibition of complex II and the tricarboxylic acid cycle, and synergistically acting excitotoxicity.

Methylmalonic acidurias are biochemically characterized by an accumulation of methylmalonate (MMA) and alternative metabolites. There is growing evidence for basal ganglia degeneration in these patients. The pathomechanisms involved are still unknown, a contribution of toxic organic acids, in particular MMA, has been suggested. Here we report that MMA induces neuronal damage in cultures of embryonic rat striatal cells at a concentration range encountered in affected patients. MMA-induced cell damage was reduced by ionotropic glutamate receptor antagonists, antioxidants, and succinate. These results suggest the involvement of secondary excitotoxic mechanisms in MMA-induced cell damage. MMA has been implicated in inhibition of respiratory chain complex II. However, MMA failed to inhibit complex II activity in submitochondrial particles from bovine heart. To unravel the mechanism underlying neuronal MMA toxicity, we investigated the formation of intracellular metabolites in MMA-loaded striatal neurons. There was a time-dependent intracellular increase in malonate, an inhibitor of complex II, and 2-methylcitrate, a compound with multiple inhibitory effects on the tricarboxylic acid cycle, suggesting their putative implication in MMA neurotoxicity. We propose that neuropathogenesis of methylmalonic aciduria may involve an inhibition of complex II and the tricarboxylic acid cycle by accumulating toxic organic acids, and synergistic secondary excitotoxic mechanisms.

Animals↗

PubMed2002

Evaluation of 6-year application of the enzymatic colorimetric phenylalanine assay in the setting of neonatal screening for phenylketonuria.

BACKGROUND: Most reports on phenylketonuria (PKU) screening focused solely on the result of the initial investigation of the neonatal screening sample. The aim of this study was to evaluate an enzymatic phenylalanine (Phe) determination in the whole context spanning from the initial investigation over the recall period, up to the confirmation or exclusion of the disease. METHODS: Phe of dried blood spot specimens was analysed colorimetrically in a microtitre-plate assay based on the L-phenylalanine dehydrogenase reaction coupled with an intermediate electron acceptor system. This assay was evaluated for analytical variables and for neonatal PKU screening in a total number of 423,773 neonates during a 6-year period. RESULTS: Method validation with respect to linearity, precision (within-run CVs 3.4-4.2%, between-run CVs 6.2-10.4%), and accuracy fulfilled all requirements for a screening method. Mean Phe (+/-SD) of 130,000 healthy neonates was 84 (+/-22) micromol/l with a cut-off point (mean+3 SD) of 150 micromol/l. From 423,773 neonates, hyperphenylalaninemia was confirmed in 155 cases and further differentiated into PKU (41 cases, 27%), BH(4) deficiency (3, 2%), non-PKU HPA (67, 43%), transient neonatal HPA (28, 18%), and secondary HPA (16, 10%). The number of false-positives (recall-rate) was 0.23%, and no false-negatives were noted. CONCLUSIONS: Detailed studies over a period of 6 years including more than 400,000 neonates clearly show that the enzymatic assay is a reliable and sensitive method for neonatal screening of PKU. The proven prevalence of non-PKU HPA in the German population disclosed by the assay was twice as high as compared to the "Guthrie test" used previously. The growing use and application of tandem mass spectrometry in neonatal screening will not derogate the usefulness of the enzymatic assay in PKU screening in the foreseeable future. Careful analysis of our screening results and monitoring of all pathological samples resulted in an evidence-based flow chart for a rational PKU screening.

Amino Acid Metabolism, Inborn Errors↗