The glucose-6-phosphate dehydrogenase (G6PD) deficient variant G6PD Union (454 Arg-->Cys) has a worldwide distribution possibly due to recurrent mutation

Pathogenic G6PD variants: Different clinical pictures arise from different missense mutations in the same codon

G6PD deficiency results from mutations in the X-linked G6PD gene. More than 200 variants are associated with enzyme deficiency: each one of them may either cause predisposition to haemolytic anaemia triggered by exogenous agents (class B variants), or may cause a chronic haemolytic disorder (class A variants). Genotype-phenotype correlations are subtle. We report a rare G6PD variant, discovered in a baby presenting with severe jaundice and haemolytic anaemia since birth: the mutation of this class A variant was found to be p.(Arg454Pro). Two variants affecting the same codon were already known: G6PD Union, p.(Arg454Cys), and G6PD Andalus, p.(Arg454His). Both these class B variants and our class A variant exhibit severe G6PD deficiency. By molecular dynamics simulations, we performed a comparative analysis of the three mutants and of the wild-type G6PD. We found that the tetrameric structure of the enzyme is not perturbed in any of the variants; instead, loss of the positively charged Arg residue causes marked variant-specific rearrangement of hydrogen bonds, and it influences interactions with the substrates G6P and NADP. These findings explain severe deficiency of enzyme activity and may account for p.(Arg454Pro) expressing a more severe clinical phenotype.

Fine Mapping of Glucose 6 Phosphate Dehydrogenase (G6PD) Deficiency in a Rural Malaria Area of South West Odisha Using the Clinical, Hematological and Molecular Approach

Introduction

The aim of the study was to enumerate the clinical, hematological, and molecular spectrum of G6PD deficiency in malaria endemic regions of south west Odisha.

Methods

Diagnosis of G6PD deficiency was made by using the Di-chloroindophenol Dye test in two south west districts (Kalahandi and Rayagada) of Odisha State. Demographic and clinical history was taken from each individual using a pre-structured questionnaire. Molecular characterization of G6PD deficiency was done using PCR-RFLP and Sanger sequencing.

Results

A total of 1981 individuals were screened; among them, 59 (2.97%) individuals were G6PD deficient. The analysis revealed that G6PD deficiency was more among males (4.0%) as compared to females (2.3%). Prevalence of G6PD deficiency was significantly higher among tribal populations (4.8%) as compared to non-tribal populations (2.4%) (p=0.012, OR=2.014, 95%CI=1.206–3.365). Twenty four individuals with G6PD deficiency had mild to moderate anemia, whereas 26 G6PD deficient individuals had a history of malaria infection. Among them, 3 (11.5%) required blood transfusion during treatment. Molecular analysis revealed G6PD Orissa as the most common (88%) mutation in the studied cohort. G6PD Kaiping (n=3), G6PD Coimbra (n=2) and G6PD Union (n=1) were also noted in this cohort.

Conclusion

The cumulative prevalence of G6PD deficiency in the present study is below the estimated national prevalence. G6PD deficiency was higher among tribes as compared to non-tribes. Clinical significance for G6PD deficiency was noted only in malaria infected individuals. Rare G6PD Kaiping and G6PD Union variants were also present.

Genotype-Phenotype Correlations of Glucose-6-Phosphate-Deficient Variants Throughout an Activity Distribution

BACKGROUND

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is an X-linked disorder that may manifest as neonatal jaundice or acute hemolytic anemia. Quantitative assessment of G6PD activity in erythrocytes is required to definitively diagnose a deficiency. Most males and homozygous females have low enzyme activities, whereas heterozygous females may have a range of activities. We sought to examine G6PD genotype-phenotype associations to identify an activity cutoff above which G6PD deficiency is unlikely.

METHODS

Ninety-five residual samples were randomly selected to represent the various regions of a G6PD activity distribution. DNA was isolated from the leukocyte fraction and sequenced using the Sanger method. ROC curves were used to establish cutoffs.

RESULTS

Thirteen variant alleles were identified, including 1 not previously reported. In the very deficient activity range, we found males and homozygous females of both class II and III variants. In the deficient category, we found predominantly class III males and heterozygous females. The presumed deficient category contained class III and IV variants and nonvariants. An activity cutoff of <7.85 U/g hemoglobin (Hb) was 100% sensitive and 94% specific for identifying a G6PD-deficient male, and a cutoff of <8.95 U/g Hb was 90% sensitive and 82% specific for a deficient female.

CONCLUSIONS

The observed activity groupings were not because of a particular variant class. Cutoffs to identify the presence of a deficiency variant for males and females may be useful when trying to decide whether to recommend genetic analysis.

Path to facilitate the prediction of functional amino acid substitutions in red blood cell disorders--a computational approach

Background

A major area of effort in current genomics is to distinguish mutations that are functionally neutral from those that contribute to disease. Single Nucleotide Polymorphisms (SNPs) are amino acid substitutions that currently account for approximately half of the known gene lesions responsible for human inherited diseases. As a result, the prediction of non-synonymous SNPs (nsSNPs) that affect protein functions and relate to disease is an important task.

Principal Findings

In this study, we performed a comprehensive analysis of deleterious SNPs at both functional and structural level in the respective genes associated with red blood cell metabolism disorders using bioinformatics tools. We analyzed the variants in Glucose-6-phosphate dehydrogenase (G6PD) and isoforms of Pyruvate Kinase (PKLR & PKM2) genes responsible for major red blood cell disorders. Deleterious nsSNPs were categorized based on empirical rule and support vector machine based methods to predict the impact on protein functions. Furthermore, we modeled mutant proteins and compared them with the native protein for evaluation of protein structure stability.

Significance

We argue here that bioinformatics tools can play an important role in addressing the complexity of the underlying genetic basis of Red Blood Cell disorders. Based on our investigation, we report here the potential candidate SNPs, for future studies in human Red Blood Cell disorders. Current study also demonstrates the presence of other deleterious mutations and also endorses with in vivo experimental studies. Our approach will present the application of computational tools in understanding functional variation from the perspective of structure, expression, evolution and phenotype.

G6PD deficiency: the genotype-phenotype association

Deficiency of glucose-6-phosphate dehydrogenase is a very common X-linked genetic disorder though most deficient people are asymptomatic. A number of different G6PD variants have reached polymorphic frequencies in different parts of the world due to the relative protection they confer against malaria infection. People, usually males, with deficient alleles are susceptible to neonatal jaundice, and acute hemolytic anemia, usually during infection, after treatment with certain drugs or after eating fava beans. Very rarely de novo mutations can arise causing the more severe condition of chronic nonspherocytic hemolytic anemia. Altogether 160 different mutations have been described. The majority of mutations cause red cell enzyme deficiency by decreasing enzyme stability. The polymorphic mutations affect amino acid residues throughout the enzyme and decrease the stability of the enzyme in the red cell, possibly by disturbing protein folding. The severe mutations mostly affect residues at the dimer interface or those that interact with a structural NADP molecule that stabilizes the enzyme.

Characterization of G6PD deficiency in southern Croatia: description of a new variant, G6PD Split

Glucose-6-phosphate dehydrogenase (G6PD) deficiency protects from severe forms of malaria. It is interesting therefore to analyze the molecular basis underlying G6PD deficiency in regions such as the Mediterranean basin where malaria was present for a long time in history. Here we report on the genetic characterization of G6PD deficiency among inhabitants of one Mediterranean region-the Dalmatian region of south Croatia. We analyzed 24 unrelated G6PD-deficient male subjects. Molecular testing revealed several different mutations: G6PD Cosenza 9, G6PD Mediterranean 4, G6PD Seattle 3, G6PD Union 3, and G6PD Cassano 1. Furthermore, we have identified one novel G6PD variant that we named G6PD Split. This variant is caused by a nucleotide change 1442 C-->G leading to the amino acid substitution 481 Pro-->Arg and is characterized by moderate enzyme deficiency (class III variant). This study reveals a higher prevalence (37.5%) of the Cosenza mutation in the Dalmatian region than anywhere else previously investigated and overall shows the considerable molecular heterogeneity underlining G6PD deficiency that can be observed in Mediterranean populations.

Molecular Analysis of Eight Biochemically Unique Glucose-6-Phosphate Dehydrogenase Variants Found in Japan

We analyzed the molecular mutations of eight known Japanese glucose-6-phosphate dehydrogenase (G6PD) variants with unique biochemical properties. Three of them were caused by novel missense mutations: G6PD Musashino by 185 C→T, G6PD Asahikawa by 695 G→A, and G6PD Kamiube by 1387 C→T. Predicted amino acid substitutions causing asymptomatic variants G6PD Musashino (62 Pro→Phe) and G6PD Kamiube (463 Arg→Cys) were located in regions near the amino or carboxyl end of the polypeptide chain, whereas an amino acid change 232 Cys→Tyr causing a class 1 variant G6PD Asahikawa was located in the region where amino acid alterations in some class 1 variants were clustered. The other five variants had known missense mutations, namely, G6PD Fukushima, 1246 G→A, G6PD Morioka, 1339 G→A, and G6PD Iwate, G6PD Niigata and G6PD Yamaguchi, 1160 G→A, which cause variants, G6PD Tokyo, G6PD Santiago de Cuba, and G6PD Beverly Hills, respectively.

Molecular genetics of glucose-6-phosphate dehydrogenase deficiency in Mexico

Several studies carried out between 1965 and 1985 showed that G-6-PD deficiency in Mexico is heterogeneous at the biochemical level and that the G-6-PD A- phenotype is relatively common. We have now investigated the molecular basis of G-6-PD deficiency in Mexico. Up-to-date 60 chromosomes with G6PD mutations have been studied, 16 in previous studies and 44 in the present work. Molecular analysis of DNA from G-6-PD deficient Mexican mestizos and their relatives show that G-6-PD A- genotypes are relatively common but also that in Mexico G-6-PD deficiency is heterogeneous at the DNA level. Thus, five different genotypes have been observed: G-6-PD A-(202A/376G) (41 chromosomes), G-6-PD A-(376G/968C) (14 chromosomes), G-6-PD Seattle844C (3 chromosomes), G-6-PD "Mexico City"680A (1 chromosome) and G-6-PD Guadalajara1159T (1 chromosome). The G-6-PD A-(202A/376G), G-6-PD A-(376G/968C) and G-6-PD Seattle844C mutations in Mexico are on the same Pvu II/ Pst I/ 1311 / Nla III haplotypes as found in individuals from Africa, Spain and the Canary Islands. Consequently, these mutations were probably imported to Mexico through African slaves and/or the Spanish immigrants during and after the colonization.

Molecular genetics of glucose-6-phosphate dehydrogenase (G6PD) deficiency in Spain: identification of two new point mutations in the G6PD gene

In order to explore the nature of glucose-6-phosphate dehydrogenase (G6PD) deficiency in Spain, we have analysed the G6PD gene in 11 unrelated Spanish G6PD-deficient males and their relatives by using the polymerase chain reaction and single-strand conformation polymorphism (PCR-SSCP) analysis combined with a direct PCR-sequencing procedure and PCR-restriction enzyme (RE) analysis. We have identified eight different missense mutations, six of which have been reported in previously described G6PD variants. In nine patients who had presented with acute favism we found the following mutations: G6PD A-376G-202A (four cases), G6PD Union1360T (two cases), G6PD Mediterranean563T (one case) and G6PD Aures143C (one case). In the remaining patient a novel A to G transition was found at nucleotide position 209 which has not been reported in any other ethnic group. This mutation results in a (70) Tyr to Cys substitution and the resulting G6PD variant was biochemically characterized and designated as G6PD Murcia. This new mutation creates a Bsp 1286I recognition site which enabled us to rapidly detect it by PCR-RE analysis. In two patients with chronic non-spherocytic haemolytic anaemia (CNSHA) we found the underlying genetic defects, as had been noted previously, to be located within a cluster of mutations in exon 10. One of them had the T to C transition at nucleotide 1153, causing a (385) Cys to Arg substitution, previously described in G6PD Tomah. The other, previously reported as having a variant called G6PD Clinic, has a G to A transition at nucleotide 1215 that produces a (405) Met to Ile substitution, thus confirming that G6PD Clinic is a new class I variant.