Multiplex Snapshot minisequencing for the detection of common PAH gene mutations in Iranian patients with Phenylketonuria

Background

Phenylketonuria is a common inborn defect of amino acid metabolism in the world. This failure is caused by an autosomal recessive insufficiency of the hepatic enzyme hyperphenylalaninemia (PAH), which catalyzes the irreversible hydroxylation of phenylalanine to tyrosine. More than 1,040 different disease-causing mutations have already been identified in the PAH gene. The most prominent complication of Phenylketonuria, if not diagnosed and treated, is severe mental retardation. Hence, early diagnosis and initiation of nutritional therapy are the most significant measures in preventing this mental disorder. Given these data, we developed a simple and rapid molecular test to detect the most frequent PAH mutations.

Methods

Multiplex assay was developed based on the SNaPshot minisequencing approach to simultaneously perform genotyping of the 10 mutations at the PAH gene. We optimized detection of these mutations in one multiplex PCR, followed by 10 single-nucleotide extension reactions. DNA sequencing assay was also used to verify genotyping results obtained by SNaPshot minisequencing.

Result

All 10 genotypes were determined based on the position and the fluorescent color of the peaks in a single electropherogram. Sequencing results of these frequent mutations showed that by using this method, a 100% detection rate could be achieved in the Iranian population.

Conclusion

SNaPshot minisequencing can be useful as a secondary test in neonatal screening for HPA in neonates with a positive screening test, and it is also suitable for carrier screening. The assay can be easily applied for accurate and time- and cost-efficient genotyping of the selected SNPs in various population.

[Screening of phenylketonuria and analysis of phenylalanine hydroxylase gene in 380 996 newborns from Hainan province]

Objective: To investigate the incidence of phenylketonuria and distribution characteristics of phenylalanine hydroxylase (PAH) gene in newborns from Hainan province. Methods: Dry blood spot specimens of heels from 380 996 newborns in Hainan province from January 2017 to December 2019 were collected. Phenylalanine (Phe) concentrations in these dry blood spots were measured by the fluorescence method to screen phenylketonuria (PKU). A second dry blood spot sample will be collected if suspicious samples were detected after initial screening. Tandem mass spectrometry were used to detect the concentrations of Phe and tyrosine. Urine samples of the suspected newborns were sent out for urotrexate spectrum analysis and tetrahydrobiopterin loading test. PCR and flow-through rapid hybridization method were employed to detect PAH gene mutations. Meanwhile, peripheral blood samples of suspicious newborns of PKU and their parents were collected to perform gene sequencing. Results: Among the 380 996 newborns, 39 were suspected and 14 were diagnosed with PKU, including 11 cases of PAH deficiency and 3 cases of tetrahydrobiopterin deficiency. Of 14 confirmed cases, there were 8 male cases and 6 female cases. In the newborn population of Hainan province, the annual incidence of PKU was 1.22/100 000. Thirteen PAH gene mutations were detected in confirmed cases: c.728G>A, c.158G>A, c.1238G>C, c.611A>G, c.1068C>A, c.706+5G>A, c.740G>T, c.1081A>T, c.793T>G, c.1223G>A, c.721C>T, c.331C>T and c.1174T>A. Conclusions: PKU has a high incidence in newborn population of Hainan province in the past three years. The PAH gene has a wide spectrum of mutations. Two rare mutations were also found: c.793T>G and c.706+5G>A.

Identification of a Novel Mutation in the PAH Gene in an Iranian Phenylketonuria Family: A Case Report

Phenylketonuria (PKU) is an inborn error of amino acid metabolism with an autosomal recessive inheritance caused in most cases by mutations in the phenylalanine hydroxylase (PAH) gene. PKU has wide allelic heterogeneity. Here we report a novel heterozygous substitution (c.1223G>T (p.Arg408Leu)) in the PAH gene in an Iranian PKU family. The patient was 19-yr-old female with diagnosis of moderate PKU referred to Department of Medical Genetics, Tehran University of Medical Sciences, Tehran, Iran for genetic counseling/analysis in April 2015. We used PCR-Sequencing to identify any sequence variations in the PAH gene.

A Novel Variant in the PAH Gene Causing Phenylketonuria in an Iranian Pedigree

BACKGROUND

Phenylalanine hydroxylase (PAH) gene is the well-known causative gene for classic Phenylketonuria (PKU) (OMIM#261600) disease, with more than 500 reported mutations. Through this study, a novel mutation in the PAH gene in an Iranian pedigree with phenylketonuria was introduced.

METHODS

A consanguineous family with a 10-year old affected girl was referred for genetic analysis. Mutation screening of all exons and exon-intron boundaries was performed by Sanger sequencing, and mini haplotype analysis was carried out by genotyping of Short Tandem Repeat (STR) and Variable Number Tandem Repeat (VNTR) alleles.

RESULTS

Mutation analysis revealed a novel homozygous insertion of a single adenine nucleotide at position 335 in exon 3 of the PAH gene. Based on the American College of Medical Genetics and Genomics (ACMG) guidelines, the change is interpreted as a pathogenic mutation which produces a premature termination signal (TAA) at codon 113 according to in silico assessments. The mini haplotype analysis showed that this mutation was linked to STR (15) -VNTR (3).

CONCLUSION

In this study, a novel mutation was reported in a patient who had PKU symptoms without any previously reported mutations in the PAH gene (NM_000277.1:p.Asp112Glufs*2) that can be responsible for the classical PKU phenotype in the Iranian population. Detection of novel mutations indicates notable allelic heterogeneity of the PAH locus among this population.

[Phenotypic and molecular characterization of a Colombian family with phenylketonuria]

INTRODUCTION

Phenylketonuria is a metabolic disorder characterized by severe neurological involvement and behavioral disorder, whose early diagnosis enables an effective treatment to avoid disease sequelae, thus changing the prognosis. Objective: To characterize a family with phenylketonuria in Colombia at clinical, biochemical and molecular levels. Materials and methods: The population consisted of seven individuals of a consanguineous family with four children with suggestive symptoms of phenylketonuria. After signing an informed consent, blood and urine samples were taken for colorimetric tests and high performance liquid and thin layer chromatographies. DNA extraction and sequencing of the 13 exons of the PAH gene were performed in all subjects. We designed primers for each exon with the Primer 3 software using automatic sequencing equipment Abiprism 3100 Avant. Sequences were analyzed using the SeqScape, v2.0, software. Results: We described the clinical and molecular characteristics of a Colombian family with phenylketonuria and confirmed the presence of the mutation c.398_401delATCA. We established a genotype-phenotype correlation, highlighting the interesting clinical variability found among the affected patients despite having the same mutation in all of them. Conclusions: Early recognition of this disease is very important to prevent its neurological and psychological sequelae, given that patients reach old age without diagnosis or proper management.

Preparation of a selective L-phenylalanine imprinted polymer implicated in patients with phenylketonuria

BACKGROUND

Molecular imprinting is a method for synthesizing polymers with structure-selective adsorption properties with applications such as, selectivity binding, drug delivery systems and anti-bodies. The present study aims at optimizing the preparation of molecularly imprinted polymer (MIP) against l-phenylalanine, in order to increase phenylalanine-binding in Enzymatic Intestinal Simulated Fluid (ESIF).

METHODS

The MIP for l-phenylalanine, as a water-soluble template, was successfully synthesized without derivatization. Synthesization was done by a UV polymerization method in which methacrylic acid (MAA), as a functional monomer, and ethylene glycol dimethacrylate (EGDMA), as a cross-linker, were used in the presence of five different porogenic solvents including; acetonitrile, tetrahydrofuran (THF), chloroform, toluene and dimethyl sulfoxide (DMSO). The selectivity of the MIP was examined using 19 different amino acids in human serum and was evaluated by HPLC. In addition, morphological studies were conducted using SEM.

RESULTS

The results showed that the obtained MIP with acetonitrile had the highest capacity and selectivity compared with other solvents. The data indicated that Phe-binding to MIP was significantly more than the former binding to NIP in EISF (P≤0.05). Moreover, in comparison with NIP and control group, MIP showed a better selectivity and binding for Phe. This could be used for the reduction of Phe in human serum samples of Phenylketonuria.

CONCLUSION

Our findings suggest that the MIP against Phe prepared with acetonitrile, showed a good selectivity and binding, which caused a reduction of blood Phe concentration in enzymatic simulated intestinal fluid and human serum sample of Phenylketonuria.

Quality of Life and the Associated Psychological Factors in Caregivers of Children with PKU

OBJECTIVES

The main objective of this study was to investigate the association of psychological factors and life stressors with quality of life in caregivers of children with PKU.

METHODS

Participants were caregivers of children with PKU who were referred to a child and adolescent consultation-liaison psychiatry clinic for a clinical follow up. Their demographic characteristics were recorded at first. WHOQOL-BREF and Depression-Anxiety-Stress Scale (DASS) were used to assess quality of life, depression, anxiety and stress in participants. Data analysis was performed using SPSS-11.5 statistical software.

RESULTS

A total number of 49 caregivers were enrolled for the study. The mean age of participants and their children were 35.63±8.82, and 9.84±6.62 respectively. Of the participants, 59.2% were mothers and 40.8% were fathers. Of the children, 51% were girls and 49% were boys. According to the results, 57.1, 50.1 and 57.1 percent of the participants had mild to severe levels of depression, anxiety and stress scores respectively. The most associated factors with quality of life were as follows: caregivers' occupation; anxiety; and depression mean scores.

CONCLUSION

Results of the current study showed that caregivers of children with PKU have lower levels of quality of life in comparison with the general population; and the most correlated factors with quality of life were the caregivers' occupation (especially unemployment), and high levels of depression and anxiety.