RESUMO

Mucopolysaccharidosis type IIIC (MPSIIIC) is a severe, rare autosomal recessive disorder caused by variants in the heparan-α-glucosaminide N-acetyltransferase (HGSNAT) gene which result in lysosomal accumulation of heparan sulfate. We analyzed clinical presentation, molecular defects and their haplotype context in 78 (27 novel) MPSIIIC cases from 22 countries, the largest group studied so far. We describe for the first time disease-causing variants in the patients from Brazil, Algeria, Azerbaijan, and Iran, and extend their spectrum within Canada, Colombia, Turkey, and the USA. Six variants are novel: two missense, c.773A>T/p.N258I and c.1267G>T/p.G423W, a nonsense c.164T>A/p.L55*, a splice-site mutation c.494-1G>A/p.[P165_L187delinsQSCYVTQAGVRWHHLGSLQALPPGFTPFSYLSLLSSWNC,P165fs], a deletion c.1348delG/p.(D450fs) and an insertion c.1479dupA/p.(Leu494fs). The missense HGSNAT variants lacked lysosomal targeting, enzymatic activity, and likely the correct folding. The haplotype analysis identified founder mutations, p.N258I, c.525dupT, and p.L55* in the Brazilian state of Paraiba, c.493+1G>A in Eastern Canada/Quebec, p.A489E in the USA, p.R384* in Poland, p.R344C and p.S518F in the Netherlands and suggested that variants c.525dupT, c.372-2G>A, and c.234+1G>A present in cis with c.564-98T>C and c.710C>A rare single-nucleotide polymorphisms, have been introduced by Portuguese settlers in Brazil. Altogether, our results provide insights into the origin, migration roots and founder effects of HGSNAT disease-causing variants, and reveal the evolutionary history of MPSIIIC.

Assuntos

Acetiltransferases/genética , Mucopolissacaridose III/genética , Mutação , Acetiltransferases/química , Argélia , Animais , Azerbaijão , Brasil , Células COS , Canadá , Chlorocebus aethiops , Colômbia , Evolução Molecular , Feminino , Efeito Fundador , Haplótipos , Humanos , Irã (Geográfico) , Masculino , Países Baixos , Linhagem , Filogeografia , Polônia , Dobramento de Proteína

RESUMO

BACKGROUND: Genetic heterogeneity and compound heterozygosis give rise to a continuous spectrum of phenylalanine hydroxylase deficiency and metabolic phenotypes in phenylketonuria (PKU). The most used parameters for evaluating phenotype in PKU are pretreatment phenylalanine (Phe) levels, tolerance for dietary Phe, and Phe overloading test. Phenotype can vary from a "classic" (severe) form to mild hyperphenylalaninemia, which does not require dietary treatment. A subset of patients is responsive to treatment by the cofactor tetrahydrobiopterin (BH4 ). Genotypes of PKU patients from Rio de Janeiro, Brazil, were compared to predicted and observed phenotypes. Genotype-based estimations of responsiveness to BH4 were also conducted. METHODS: Phenotype was defined by pretreatment Phe levels. A standard prediction system based on arbitrary assigned values was employed to measure genotype-phenotype concordance. Patients were also estimated as BH4 -responders according to the responsiveness previously reported for their mutations and genotypes. RESULTS: A 48.3% concordance rate between genotype-predicted and observed phenotypes was found. When the predicted phenotypes included those reported at the BIOPKU database, the concordance rate reached 77%. A total of 18 genotypes from 30 patients (29.4%) were estimated as of potential or probable BH4 responsiveness. Inconsistencies were observed in genotypic combinations including the common "moderate" mutations p.R261Q, p.V388M, and p.I65T and the mild mutations p.L48S, p.R68S, and p.L249F. CONCLUSION: The high discordance rate between genotype-predicted and observed metabolic phenotypes in this study seems to be due partially to the high frequency of the so-called "moderate" common mutations, p.R261Q, p.V388M, and p.I65T, which are reported to be associated to erratic or more severe than expected metabolic phenotypes. Although our results of BH4 estimated responsiveness must be regarded as tentative, it should be emphasized that genotyping and genotype-phenotype association studies are important in selecting patients to be offered a BH4 overload test, especially in low-resource settings like Brazil.

Assuntos

Biopterinas/análogos & derivados , Genótipo , Variantes Farmacogenômicos , Fenótipo , Fenilcetonúrias/genética , Biopterinas/uso terapêutico , Brasil , Humanos , Fenilalanina Hidroxilase/genética , Fenilcetonúrias/tratamento farmacológico

RESUMO

BACKGROUND: Phenylketonuria (PKU) is an autosomal recessive disease resulting from mutations in the PAH gene. Most of the patients are compound heterozygotes, and genotype is a major factor in determining the phenotypic variability of PKU. More than 1,000 variants have been described in the PAH gene. Rio de Janeiro's population has a predominance of Iberian, followed by African and Amerindian ancestries. It is expected that most PKU variants in this Brazilian state have originated in the Iberian Peninsula. However, rare European, African or pathogenic variants that are characteristic of the admixed population of the state might also be found. METHODS: A total of 102 patients were included in this study. Genomic DNA was isolated from dried blood spots. Sanger sequencing was used for PAH gene variant identification. Deletions and duplications were also screened using MLPA analysis. Haplotypes were also determined. RESULTS: Nine (8.8%) homozygous and 93 (91.2%) compound heterozygous patients were found. The spectrum included 37 causative mutations. Missense, nonsense, and splicing pathogenic variants corresponded to 63.7%, 2.9%, and 22.6% of the mutant alleles, respectively. Large (1.5%), and small deletions, inframe (5.4%) and with frameshift (3.9%), comprised the remainder. The most frequent pathogenic variants were: p.V388M (12.7%), p.R261Q (11.8%), IVS10-11G>A (10.3%), IVS2+5G>C (6.4%), p.S349P (6.4%), p.R252W (5.4%), p.I65T (4.4%), p.T323del (4.4%), and p.P281L (3.4%). One novel variant was detected: c.934G>T (p.G312C) [rs763115697]. CONCLUSION: The three most frequent pathogenic variants in our study (34.8% of the alleles) were also the most common in other Brazilian states, Portugal, and Spain (p.V388M, p.R261Q, IVS10-11G>A), corroborating that the Iberian Peninsula is the major source of PAH mutations in Rio de Janeiro. Pathogenic variants that have other geographical origins, such IVS2+5G>C, p.G352Vfs*48, and IVS12+1G>A were also detected. Genetic drift and founder effect may have also played a role in the mutation spectrum we observed.

RESUMO

O objetivo deste trabalho foi identificar o perfil eletroforético das proteínas plasmáticas e diferenciar suas frações protéicas. Foram utilizadas amostras de plasma coletadas de um casal de emus clinicamente saudáveis, processadas pela técnica do biureto e eletroforese em gel de agarose. Foram encontrados valores de 5,30 g/dL e 4,10 g/dL de proteínas plasmáticas totais e 0,67 e 0,81 para a relação entre a albumina e as globulinas, para a fêmea e o macho, respectivamente. Na diferenciação das frações, encontrou-se a presença de pré-albumina, albumina, uma fração alfa-globulina, duas frações beta-globulina, e uma fração gama-globulina, para ambos os animais.

RESUMO

O objetivo deste trabalho foi identificar o perfil eletroforético das proteínas plasmáticas e diferenciar suas frações protéicas. Foram utilizadas amostras de plasma coletadas de um casal de emus clinicamente saudáveis, processadas pela técnica do biureto e eletroforese em gel de agarose. Foram encontrados valores de 5,30 g/dL e 4,10 g/dL de proteínas plasmáticas totais e 0,67 e 0,81 para a relação entre a albumina e as globulinas, para a fêmea e o macho, respectivamente. Na diferenciação das frações, encontrou-se a presença de pré-albumina, albumina, uma fração alfa-globulina, duas frações beta-globulina, e uma fração gama-globulina, para ambos os animais.