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Zürich, Switzerland

Blau N.,University of Zurich | Blau N.,Zurich Center for Integrative Human Physiology | Blau N.,Research Center for Children | Hennermann J.B.,Charite - Medical University of Berlin | And 2 more authors.
Molecular Genetics and Metabolism

This article summarizes the present knowledge, recent developments, and common pitfalls in the diagnosis, classification, and genetics of hyperphenylalaninemia, including tetrahydrobiopterin (BH4) deficiency. It is a product of the recent workshop organized by the European Phenylketonuria Group in March 2011 in Lisbon, Portugal. Results of the workshop demonstrate that following newborn screening for phenylketonuria (PKU), using tandem mass-spectrometry, every newborn with even slightly elevated blood phenylalanine (Phe) levels needs to be screened for BH4 deficiency. Dried blood spots are the best sample for the simultaneous measurement of amino acids (phenylalanine and tyrosine), pterins (neopterin and biopterin), and dihydropteridine reductase activity from a single specimen. Following diagnosis, the patient's phenotype and individually tailored treatment should be established as soon as possible. Not only blood Phe levels, but also daily tolerance for dietary Phe and potential responsiveness to BH4 are part of the investigations. Efficiency testing with synthetic BH4 (sapropterin dihydrochloride) over several weeks should follow the initial 24-48-hour screening test with 20. mg/kg/day BH4. The specific genotype, i.e. the combination of both PAH alleles of the patient, helps or facilitates to determine both the biochemical phenotype (severity of PKU) and the responsiveness to BH4. The rate of Phe metabolic disposal after Phe challenge may be an additional useful tool in the interpretation of phenotype-genotype correlation. © 2011 Elsevier Inc. Source

Cario H.,University of Ulm | Smith D.E.C.,VU University Amsterdam | Blom H.,VU University Amsterdam | Blau N.,University of Zurich | And 13 more authors.
American Journal of Human Genetics

The importance of intracellular folate metabolism is illustrated by the severity of symptoms and complications caused by inborn disorders of folate metabolism or by folate deficiency. We examined three children of healthy, distantly related parents presenting with megaloblastic anemia and cerebral folate deficiency causing neurologic disease with atypical childhood absence epilepsy. Genome-wide homozygosity mapping revealed a candidate region on chromosome 5 including the dihydrofolate reductase (DHFR) locus. DHFR sequencing revealed a homozygous DHFR mutation, c.458A>T (p.Asp153Val), in all siblings. The patients' folate profile in red blood cells (RBC), plasma, and cerebrospinal fluid (CSF), analyzed by liquid chromatography tandem mass spectrometry, was compatible with DHFR deficiency. DHFR activity and fluorescein-labeled methotrexate (FMTX) binding were severely reduced in EBV-immortalized lymphoblastoid cells of all patients. Heterozygous cells displayed intermediate DHFR activity and FMTX binding. RT-PCR of DHFR mRNA revealed no differences between wild-type and DHFR mutation-carrying cells, whereas protein expression was reduced in cells with the DHFR mutation. Treatment with folinic acid resulted in the resolution of hematological abnormalities, normalization of CSF folate levels, and improvement of neurological symptoms. In conclusion, the homozygous DHFR mutation p.Asp153Val causes DHFR deficiency and leads to a complex hematological and neurological disease that can be successfully treated with folinic acid. DHFR is necessary for maintaining sufficient CSF and RBC folate levels, even in the presence of adequate nutritional folate supply and normal plasma folate. © 2011 The American Society of Human Genetics. All rights reserved. Source

Heintz C.,University of Zurich | Dobrowolski S.F.,University of Pittsburgh | Andersen H.S.,University of Southern Denmark | Demirkol M.,Istanbul University | And 5 more authors.
Molecular Genetics and Metabolism

In about 20-30% of phenylketonuria (PKU) patients, phenylalanine (Phe) levels can be controlled by cofactor 6R-tetrahydrobiopterin (BH4) administration. The phenylalanine hydroxylase (PAH) genotype has a predictive value concerning BH4-response and therefore a correct assessment of the mutation molecular pathology is important. Mutations that disturb the splicing of exons (e.g. interplay between splice site strength and regulatory sequences like exon splicing enhancers (ESEs)/exon splicing silencers (ESSs)) may cause different severity of PKU. In this study, we identified PAH exon 11 as a vulnerable exon and used patient derived lymphoblast cell lines and PAH minigenes to study the molecular defect that impacted pre-mRNA processing. We showed that the c.1144T>C and c.1066-3C>T mutations cause exon 11 skipping, while the c.1139C>T mutation is neutral or slightly beneficial. The c.1144T>C mutation resides in a putative splicing enhancer motif and binding by splicing factors SF2/ASF, SRp20 and SRp40 is disturbed. Additional mutations in potential splicing factor binding sites contributed to elucidate the pathogenesis of mutations in PAH exon 11.We suggest that . PAH exon 11 is vulnerable due to a weak 3' splice site and that this makes exon 11 inclusion dependent on an ESE spanning position c.1144. Importantly, this implies that other mutations in exon 11 may affect splicing, since splicing is often determined by a fine balance between several positive and negative splicing regulatory elements distributed throughout the exon. Finally, we identified a pseudoexon in intron 11, which would have pathogenic consequences if activated by mutations or improved splicing conditions.Exonic mutations that disrupt splicing are unlikely to facilitate response to BH4 and may lead to inconsistent genotype-phenotype correlations. Therefore, recognizing such mutations enhances our ability to predict the BH4-response. © 2012 Elsevier Inc.. Source

Mangold S.,RWTH Aachen | Blau N.,University of Zurich | Blau N.,Zurich Center for Integrative Human Physiology | Blau N.,Research Center for Children | And 5 more authors.
Molecular Genetics and Metabolism

Background: Cerebral folate deficiency (CFD) is increasingly recognized in various neurological conditions, raising the question of whether it might represent a clear-cut clinical syndrome. Methods: Retrospective analysis of patients with low cerebral spinal fluid (CSF) 5-methyltetrahydrofolate (5MTHF) values was performed. Results: 58 pediatric patients with low (-2nd to -3rd standard deviation) and 45 patients with very low 5MTHF values (< 3rd standard deviation) were identified, including 22 patients with defined underlying neurological conditions. The leading symptoms were mental retardation (n= 84), motor retardation (n= 75), epilepsy (n= 53), ataxia (n= 44) and pyramidal tract signs (n= 37). There was no relationship between 5MTHF levels and the severity of clinical disease, the duration of clinical disease, distinct neurological symptoms and antiepileptic drug treatment, respectively. Genetical analysis for mutations in the folate receptor 1 gene proved normal in all 16 children studied. Conclusions: For the majority of patients CFD is not a clear-cut neurometabolic syndrome but the common result of different genetic, metabolic or unknown processes. Nevertheless, CFD may represent a treatable disease-modifying factor which should therefore be addressed in prospective studies. © 2011 Elsevier Inc. Source

Werner E.R.,Innsbruck Medical University | Blau N.,University of Zurich | Blau N.,Zurich Center for Integrative Human Physiology | Blau N.,Research Center for Children | And 3 more authors.
Biochemical Journal

BH 4 (6R-L-erythro-5,6,7,8-tetrahydrobiopterin) is an essential cofactor of a set of enzymes that are of central metabolic importance, including four aromatic amino acid hydroxylases, alkylglycerol mono-oxygenase and three NOS (NO synthase) isoenzymes. Consequently, BH 4 is present in probably every cell or tissue of higher organisms and plays a key role in a number of biological processes and pathological states associated with monoamine neurotransmitter formation, cardiovascular and endothelial dysfunction, the immune response and pain sensitivity. BH 4 is formed de novo from GTP via a sequence of three enzymatic steps carried out by GTP cyclohydrolase I, 6-pyruvoyltetrahydropterin synthase and sepiapterin reductase. An alternative or salvage pathway involves dihydrofolate reductase and may play an essential role in peripheral tissues. Cofactor regeneration requires pterin-4a-carbinolamine dehydratase and dihydropteridine reductase, except for NOSs, in which the BH 4 cofactor undergoes a one-electron redox cycle without the need for additional regeneration enzymes. With regard to the regulation of cofactor biosynthesis, the major controlling point is GTP cyclohydrolase I. BH 4 biosynthesis is controlled in mammals by hormones and cytokines. BH 4 deficiency due to autosomal recessive mutations in all enzymes, except for sepiapterin reductase, has been described as a cause of hyperphenylalaninaemia. A major contributor to vascular dysfunction associated with hypertension, ischaemic reperfusion injury, diabetes and others, appears to be an effect of oxidized BH 4, which leads to an increased formation of oxygen-derived radicals instead of NO by decoupled NOS. Furthermore, several neurological diseases have been suggested to be a consequence of restricted cofactor availability, and oral cofactor replacement therapy to stabilizemutant phenylalanine hydroxylase in the BH 4-responsive type of hyperphenylalaninaemia has an advantageous effect on pathological phenylalanine levels in patients. ©The Authors Journal compilation © 2011 Biochemical Society. Source

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