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Objective: To describe the clinical, biochemical, and genetic features of both new and previously reported patients with congenital disorders of glycosylation (CDGs) diagnosed in Portugal over the last 20 years., Study Design: The cohort includes patients with an unexplained multisystem or single organ involvement, with or without psychomotor disability. Serum sialotransferrin isoforms and, whenever necessary, apolipoprotein CIII isoforms and glycan structures were analyzed. Additional studies included measurement of phosphomannomutase (PMM) activity and analysis of lipid-linked oligosaccharides in fibroblasts. Sanger sequencing and massive parallel sequencing were used to identify causal variants or the affected gene, respectively., Results: Sixty-three individuals were diagnosed covering 14 distinct CDGs; 43 patients diagnosed postnatally revealed a type 1, 14 a type 2, and 2 a normal pattern on serum transferrin isoelectrofocusing. The latter patients were identified by whole exome sequencing. Nine of them presented also a hypoglycosylation pattern on apolipoprotein CIII isoelectrofocusing, pointing to an associated O-glycosylation defect. Most of the patients (62%) are PMM2-CDG and the remaining carry pathogenic variants in ALG1, ATP6AP1, ATP6AP2, ATP6V0A2, CCDC115, COG1, COG4, DPAGT1, MAN1B1, SLC35A2, SRD5A3, RFT1, or PGM1., Conclusions: Portuguese patients with CDGs are presented in this report, some of them showing unique clinical phenotypes. Among the 14 genes mutated in Portuguese individuals, 8 are shared with a previously reported Spanish cohort. However, regarding the mutational spectrum of PMM2-CDG, the most frequent CDG, a striking similarity between the 2 populations was found, as only 1 mutated allele found in the Portuguese group has not been reported in Spain., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Background: The impairment of the hepatic enzyme phenylalanine hydroxylase (PAH) causes elevation of phenylalanine levels in blood and other body fluids resulting in the most common inborn error of amino acid metabolism (phenylketonuria). Persistently high levels of phenylalanine lead to irreversible damage to the nervous system. Therefore, early diagnosis of the affected individuals is important, as it can prevent clinical manifestations of the disease., Methods: In this report, the biochemical and genetic findings performed in 223 patients diagnosed through the Portuguese Neonatal Screening Program (PNSP) are presented., Results: Overall, the results show that a high overlap exists between different types of variants and phenylalanine levels. Molecular analyses reveal a wide mutational spectrum in our population with a total of 56 previously reported variants, most of them found in compound heterozygosity (74% of the patients). Intragenic polymorphic markers were used to assess the haplotypic structure of mutated chromosomes for the most frequent variants found in homozygosity in our population (p.Ile65Thr, p.Arg158Gln, p.Leu249Phe, p.Arg261Gln, p.Val388Met, and c.1066-11G>A)., Conclusion: Our data reveal high heterogeneity at the biochemical and molecular levels and are expected to provide a better understanding of the molecular basis of this disease and to provide clues to elucidate genotype-phenotype correlations., (© 2021 The Authors. Molecular Genetics & Genomic Medicine published by Wiley Periodicals LLC.)

Background: The pyruvate dehydrogenase complex (PDC) catalyzes the irreversible decarboxylation of pyruvate into acetyl-CoA. PDC deficiency can be caused by alterations in any of the genes encoding its several subunits. The resulting phenotype, though very heterogeneous, mainly affects the central nervous system. The aim of this study is to describe and discuss the clinical, biochemical and genotypic information from thirteen PDC deficient patients, thus seeking to establish possible genotype-phenotype correlations., Results: The mutational spectrum showed that seven patients carry mutations in the PDHA1 gene encoding the E1α subunit, five patients carry mutations in the PDHX gene encoding the E3 binding protein, and the remaining patient carries mutations in the DLD gene encoding the E3 subunit. These data corroborate earlier reports describing PDHA1 mutations as the predominant cause of PDC deficiency but also reveal a notable prevalence of PDHX mutations among Portuguese patients, most of them carrying what seems to be a private mutation (p.R284X). The biochemical analyses revealed high lactate and pyruvate plasma levels whereas the lactate/pyruvate ratio was below 16; enzymatic activities, when compared to control values, indicated to be independent from the genotype and ranged from 8.5% to 30%, the latter being considered a cut-off value for primary PDC deficiency. Concerning the clinical features, all patients displayed psychomotor retardation/developmental delay, the severity of which seems to correlate with the type and localization of the mutation carried by the patient. The therapeutic options essentially include the administration of a ketogenic diet and supplementation with thiamine, although arginine aspartate intake revealed to be beneficial in some patients. Moreover, in silico analysis of the missense mutations present in this PDC deficient population allowed to envisage the molecular mechanism underlying these pathogenic variants., Conclusion: The identification of the disease-causing mutations, together with the functional and structural characterization of the mutant protein variants, allow to obtain an insight on the severity of the clinical phenotype and the selection of the most appropriate therapy.

Classic galactosemia is an autosomal recessive disorder caused by deficient galactose-1-phosphate uridylyltransferase (GALT) activity. Patients develop symptoms in the neonatal period, which can be ameliorated by dietary restriction of galactose. Many patients develop long-term complications, with a broad range of clinical symptoms whose pathophysiology is poorly understood. The high allelic heterogeneity of GALT gene that characterizes this disorder is thought to play a determinant role in biochemical and clinical phenotypes. We aimed to characterize the mutational spectrum of GALT deficiency in Portugal and to assess potential genotype-phenotype correlations. Direct sequencing of the GALT gene and in silico analyses were employed to evaluate the impact of uncharacterized mutations upon GALT functionality. Molecular characterization of 42 galactosemic Portuguese patients revealed a mutational spectrum comprising 14 nucleotide substitutions: ten missense, two nonsense and two putative splicing mutations. Sixteen different genotypic combinations were detected, half of the patients being p.Q188R homozygotes. Notably, the second most frequent variation is a splicing mutation. In silico predictions complemented by a close-up on the mutations in the protein structure suggest that uncharacterized missense mutations have cumulative point effects on protein stability, oligomeric state, or substrate binding. One splicing mutation is predicted to cause an alternative splicing event. This study reinforces the difficulty in establishing a genotype-phenotype correlation in classic galactosemia, a monogenic disease whose complex pathogenesis and clinical features emphasize the need to expand the knowledge on this "cloudy" disorder.

Maple syrup urine disease is an autosomal recessive disorder of branched-chain amino acids metabolism with a worldwide frequency of 1/185,000 live newborns. In Portugal, the incidence of the disease has not been assessed. Based on the review of the cases diagnosed by tandem mass spectrometry an incidence of 1/86,800 live newborns was estimated in Portugal, indicating that the disease is more frequent in this country than reported in most populations., (Copyright 2010 Elsevier Inc. All rights reserved.)

Maple syrup urine disease (MSUD) is an autosomal recessive disorder, caused by the defective function of the branched-chain alpha-ketoacid dehydrogenase complex (BCKD). BCKD is a mitochondrial complex, encoded by four nuclear genes (BCKDHA, BCKDHB, DBT and DLD), involved in the metabolism of branched-chain amino acids (BCAAs). Since the MSUD mutational spectrum has not been previously assessed in Portugal, in this study we present the molecular characterization of 30 MSUD Portuguese patients. Seventeen putative mutations have been identified (six in BCKDHA, five in BCKDHB and six in DBT); seven of them are here described for the first time. The most common mutation identified was a C deletion in BCKDHA gene (c.117delC; p.R40GfsX23), already reported in the Spanish population. Interestingly, it was found in all patients of a Gypsy community from South of the country, so a founder effect is probably responsible for the high incidence of the disease in this community. Structural models of MSUD missense mutations have been performed to understand their pathogenic effect, in order to elucidate and often to predict the severity of a mutation clinical consequence.

Methylmalonic aciduria (MMA) and homocystinuria, cblC type (MIM 277400) is the most frequent inborn error of vitamin B(12). The recent identification of the disease gene, MMACHC, has permitted preliminary genotype-phenotype correlations. We studied 24 Italian and 17 Portuguese patients with cblC defect to illustrate the spectrum of mutations in a southern European population and discuss the impact that mutation identification has on routine diagnostic procedures. Since the metabolic defect raises the serum levels of homocysteine, we also tested if variants in MTHFR-playing a key role in homocysteine remethylation pathway-could act as genetic modifier in cblC defect. We found that the c.271dupA (accounting for 55% of the MMACH alleles in our cohort) followed by c.394C>T (16%) and c.331C>T (9%) were the most frequent mutations. In our study we also identified a novel mutation (c.544T>C). On the other hand, the MTHFR genotype did not appear to influence age at onset, the clinical phenotype and outcome of patients with cblC defect. This study shows that mutation screening for the most common MMACH mutations occurring in early-onset forms (c.271dupA and c.331C>T) seems to have a high diagnostic yield in a southern European population with cblC defect. Although the identification of the gene defect per se does not predict completely time and severity of disease appearance, our data corroborate the importance of a molecular testing to offer accurate prenatal diagnosis to couples at high risk of having affected children.