Glucose-6-phosphate dehydrogenase (G-6-PD) mutations in Mexico: four new G-6-PD variants

An Overall View of the Functional and Structural Characterization of Glucose-6-Phosphate Dehydrogenase Variants in the Mexican Population

Glucose-6-phosphate dehydrogenase (G6PD) deficiency, affecting an estimated 500 million people worldwide, is a genetic disorder that causes human enzymopathies. Biochemical and genetic studies have identified several variants that produce different ranges of phenotypes; thus, depending on its severity, this enzymopathy is classified from the mildest (Class IV) to the most severe (Class I). Therefore, understanding the correlation between the mutation sites of G6PD and the resulting phenotype greatly enhances the current knowledge of enzymopathies' phenotypic and genotypic heterogeneity, which will assist both clinical diagnoses and personalized treatments for patients with G6PD deficiency. In this review, we analyzed and compared the structural and functional data from 21 characterized G6PD variants found in the Mexican population that we previously characterized. In order to contribute to the knowledge regarding the function and structure of the variants associated with G6PD deficiency, this review aimed to determine the molecular basis of G6PD and identify how these mutations could impact the structure, stability, and function of the enzyme and its relation with the clinical manifestations of this disease.

Functional interpretation, cataloging, and analysis of 1,341 glucose-6-phosphate dehydrogenase variants

Glucose-6-phosphate dehydrogenase (G6PD) deficiency affects over 500 million individuals who can experience anemia in response to oxidative stressors such as certain foods and drugs. Recently, the World Health Organization (WHO) called for revisiting G6PD variant classification as a priority to implement genetic medicine in low- and middle-income countries. Toward this goal, we sought to collect reports of G6PD variants and provide interpretations. We identified 1,341 G6PD variants in population and clinical databases. Using the ACMG standards and guidelines for the interpretation of sequence variants, we provided interpretations for 268 variants, including 186 variants that were not reported or of uncertain significance in ClinVar, bringing the total number of variants with non-conflicting interpretations to 400. For 414 variants with functional or clinical data, we analyzed associations between activity, stability, and current classification systems, including the new 2022 WHO classification. We corroborated known challenges with classification systems, including phenotypic variation, emphasizing the importance of comparing variant effects across individuals and studies. Biobank data made available by All of Us illustrate the benefit of large-scale sequencing and phenotyping by adding additional support connecting variants to G6PD-deficient anemia. By leveraging available data and interpretation guidelines, we created a repository for information on G6PD variants and nearly doubled the number of variants with clinical interpretations. These tools enable better interpretation of G6PD variants for the implementation of genetic medicine.

Glucose-6-Phosphate Dehydrogenase Deficiency and Neonatal Hyperbilirubinemia: Insights on Pathophysiology, Diagnosis, and Gene Variants in Disease Heterogeneity

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is a prevalent condition worldwide and is caused by loss-of-function mutations in the G6PD gene. Individuals with deficiency are more susceptible to oxidative stress which leads to the classical, acute hemolytic anemia (favism). However, G6PD deficiency in newborn infants presents with an increased risk of hyperbilirubinemia, that may rapidly escalate to result in bilirubin induced neurologic dysfunction (BIND). Often with no overt signs of hemolysis, G6PD deficiency in the neonatal period appears to be different in the pathophysiology from favism. This review discusses and compares the mechanistic pathways involved in these two clinical presentations of this enzyme disorder. In contrast to the membrane disruption of red blood cells and Heinz bodies formation in favism, G6PD deficiency causing jaundice is perhaps attributed to the disruption of oxidant-antioxidant balance, impaired recycling of peroxiredoxin 2, thus affecting bilirubin clearance. Screening for G6PD deficiency and close monitoring of affected infants are important aspects in neonatal care to prevent kernicterus, a permanent and devastating neurological damage. WHO recommends screening for G6PD activity of all infants in countries with high prevalence of this deficiency. The traditional fluorescent spot test as a screening tool, although low in cost, misses a significant proportion of cases with moderate deficiency or the partially deficient, heterozygote females. Some newer and emerging laboratory tests and diagnostic methods will be discussed while developments in genomics and proteomics contribute to increasing studies that spatially profile genetic mutations within the protein structure that could predict their functional and structural effects. In this review, several known variants of G6PD are highlighted based on the location of the mutation and amino acid replacement. These could provide insights on why some variants may cause a higher degree of phenotypic severity compared to others. Further studies are needed to elucidate the predisposition of some variants toward certain clinical manifestations, particularly neonatal hyperbilirubinemia, and how some variants increase in severity when co-inherited with other blood- or bilirubin-related genetic disorders.

Hematological and molecular analysis of patients with G6PD deficiency revealed coexistent hereditary spherocytosis and alpha thalassemia

BACKGROUND

Glucose-6-phosphate dehydrogenase (G6PD) deficiency, hereditary spherocytosis (HS), and alpha thalassemia (α-thal) are frequent erythrocyte pathologies with different geographic distributions worldwide. Our aim is to report hematological and molecular findings of G6PD deficient Mexican patients in coinheritance with suggestive hereditary spherocytosis (sHS) and α-thal.

METHODS

We studied 78 G6PD deficiency patients. Hematological parameters, acidified glycerol lysis test, erythrocyte morphology, electrophoresis, and hemoglobin quantification were obtained. G6PD and HBA2/HBA1 variants were identified using ARMS-PCR, Gap-PCR, or Sanger sequencing.

RESULTS

Nine G6PD variants were identified; A^-202A/376G , A^-376G/968C , and A^+376G as the most frequent. G6PD Santiago de Cuba^1339A and Kamiube^1387T were detected in Mexicans for first time. Hematological analysis revealed additional erythrocyte pathologies in 52 patients, 32 with positive osmotic fragility test and spherocytes in blood smear (suggestive hereditary spherocytosis, sHS), 12 with microcytosis and 8 with all three defects who had the most severe phenotype, with significantly lower hematological parameters (Hb, PCV, MCV, and MCH). α-thal variants (α^Hph α, α^-59C>T α and -α^3.7 ) were observed in 65% of patients with microcytosis.

CONCLUSION

Additional erythrocyte defects were observed in 69.3% of G6PD deficiency patients. We stress the importance of searching for the presence of additional erythrocyte hereditary diseases in patients with G6PD deficiency.

The New CIC Mutation Associates with Mental Retardation and Severity of Seizure in Turkish Child with a Rare Class I Glucose-6-Phosphate Dehydrogenase Deficiency

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is an X-linked recessive disease that causes acute or chronic hemolytic anemia and potentially leads to severe jaundice in response to oxidative agents. Capicua transcriptional repressor (CIC) is an important gene associated with mental retardation, autosomal dominant 45. Affiliated tissues including skin, brain, bone, and related phenotypes are intellectual disability and seizures. Clinical, biochemical, and whole exome analysis are carried out in a Turkish family. Mutation analysis of G6PD and CIC genes by Sanger sequencing in the whole family was carried out to reveal the effect of these mutations on the patient's clinical outcome. Here, we present the case of epilepsy in an 8-year-old child with a hemizygous variation in G6PD gene and heterozygous mutation in CIC gene, resulting in focal epileptiform activity and hypsarrhythmia in electroencephalography (EEG), seizures, psychomotor retardation, speech impairment, intellectual disability, developmental regression, and learning difficulties. Whole exome sequencing confirmed the diagnosis of X-linked increased susceptibility for hemolytic anemia due to G6PD deficiency and mental retardation type 45 due to CIC variant, which explained the development of epileptic seizures. Considering CIC variant and relevant relation with the severity and course of the disease, G6PD mutations sustained through the family are defined as hereditary. Our findings could represent the importance of variants found in G6PD as well as CIC genes linked to the severity of epilepsy, which was presumed based on the significant changes in protein configuration.

Effects of Single and Double Mutants in Human Glucose-6-Phosphate Dehydrogenase Variants Present in the Mexican Population: Biochemical and Structural Analysis

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is the most frequent human enzymopathy, affecting over 400 million people globally. Worldwide, 217 mutations have been reported at the genetic level, and only 19 have been found in Mexico. The objective of this work was to contribute to the knowledge of the function and structure of three single natural variants (G6PD A+, G6PD San Luis Potosi, and G6PD Guadalajara) and a double mutant (G6PD Mount Sinai), each localized in a different region of the three-dimensional (3D) structure. In the functional characterization of the mutants, we observed a decrease in specific activity, protein expression and purification, catalytic efficiency, and substrate affinity in comparison with wild-type (WT) G6PD. Moreover, the analysis of the effect of all mutations on the structural stability showed that its presence increases denaturation and lability with temperature and it is more sensible to trypsin digestion protease and guanidine hydrochloride compared with WT G6PD. This could be explained by accelerated degradation of the variant enzymes due to reduced stability of the protein, as is shown in patients with G6PD deficiency.

Diagnostic approaches for inherited hemolytic anemia in the genetic era

Inherited hemolytic anemias (IHAs) are genetic diseases that present with anemia due to the increased destruction of circulating abnormal RBCs. The RBC abnormalities are classified into the three major disorders of membranopathies, hemoglobinopathies, and enzymopathies. Traditional diagnosis of IHA has been performed via a step-wise process combining clinical and laboratory findings. Nowadays, the etiology of IHA accounts for germline mutations of the responsible genes coding for the structural components of RBCs. Recent advances in molecular technologies, including next-generation sequencing, inspire us to apply these technologies as a first-line approach for the identification of potential mutations and to determine the novel causative genes in patients with IHAs. We herein review the concept and strategy for the genetic diagnosis of IHAs and provide an overview of the preparations for clinical applications of the new molecular technologies.

Genetic Profiles of Korean Patients With Glucose-6-Phosphate Dehydrogenase Deficiency

Background

We describe the genetic profiles of Korean patients with glucose-6-phosphate dehydrogenase (G6PD) deficiencies and the effects of G6PD mutations on protein stability and enzyme activity on the basis of in silico analysis.

Methods

In parallel with a genetic analysis, the pathogenicity of G6PD mutations detected in Korean patients was predicted in silico. The simulated effects of G6PD mutations were compared to the WHO classes based on G6PD enzyme activity. Four previously reported mutations and three newly diagnosed patients with missense mutations were estimated.

Results

One novel mutation (p.Cys385Gly, labeled G6PD Kangnam) and two known mutations [p.Ile220Met (G6PD São Paulo) and p.Glu416Lys (G6PD Tokyo)] were identified in this study. G6PD mutations identified in Koreans were also found in Brazil (G6PD São Paulo), Poland (G6PD Seoul), United States of America (G6PD Riley), Mexico (G6PD Guadalajara), and Japan (G6PD Tokyo). Several mutations occurred at the same nucleotide, but resulted in different amino acid residue changes in different ethnic populations (p.Ile380 variant, G6PD Calvo Mackenna; p.Cys385 variants, Tomah, Madrid, Lynwood; p.Arg387 variant, Beverly Hills; p.Pro396 variant, Bari; and p.Pro396Ala in India). On the basis of the in silico analysis, Class I or II mutations were predicted to be highly deleterious, and the effects of one Class IV mutation were equivocal.

Conclusions

The genetic profiles of Korean individuals with G6PD mutations indicated that the same mutations may have arisen by independent mutational events, and were not derived from shared ancestral mutations. The in silico analysis provided insight into the role of G6PD mutations in enzyme function and stability.

Glucose-6-Phosphate Dehydrogenase: Update and Analysis of New Mutations around the World

Glucose-6-phosphate dehydrogenase (G6PD) is a key regulatory enzyme in the pentose phosphate pathway which produces nicotinamide adenine dinucleotide phosphate (NADPH) to maintain an adequate reducing environment in the cells and is especially important in red blood cells (RBC). Given its central role in the regulation of redox state, it is understandable that mutations in the gene encoding G6PD can cause deficiency of the protein activity leading to clinical manifestations such as neonatal jaundice and acute hemolytic anemia. Recently, an extensive review has been published about variants in the g6pd gene; recognizing 186 mutations. In this work, we review the state of the art in G6PD deficiency, describing 217 mutations in the g6pd gene; we also compile information about 31 new mutations, 16 that were not recognized and 15 more that have recently been reported. In order to get a better picture of the effects of new described mutations in g6pd gene, we locate the point mutations in the solved three-dimensional structure of the human G6PD protein. We found that class I mutations have the most deleterious effects on the structure and stability of the protein.

Functional and Biochemical Characterization of Three Recombinant Human Glucose-6-Phosphate Dehydrogenase Mutants: Zacatecas, Vanua-Lava and Viangchan

Glucose-6-phosphate dehydrogenase (G6PD) deficiency in humans causes severe disease, varying from mostly asymptomatic individuals to patients showing neonatal jaundice, acute hemolysis episodes or chronic nonspherocytic hemolytic anemia. In order to understand the effect of the mutations in G6PD gene function and its relation with G6PD deficiency severity, we report the construction, cloning and expression as well as the detailed kinetic and stability characterization of three purified clinical variants of G6PD that present in the Mexican population: G6PD Zacatecas (Class I), Vanua-Lava (Class II) and Viangchan (Class II). For all the G6PD mutants, we obtained low purification yield and altered kinetic parameters compared with Wild Type (WT). Our results show that the mutations, regardless of the distance from the active site where they are located, affect the catalytic properties and structural parameters and that these changes could be associated with the clinical presentation of the deficiency. Specifically, the structural characterization of the G6PD Zacatecas mutant suggests that the R257L mutation have a strong effect on the global stability of G6PD favoring an unstable active site. Using computational analysis, we offer a molecular explanation of the effects of these mutations on the active site.

Mutations of Glucose-6-Phosphate Dehydrogenase Durham, Santa-Maria and A+ Variants Are Associated with Loss Functional and Structural Stability of the Protein

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is the most common enzymopathy in the world. More than 160 mutations causing the disease have been identified, but only 10% of these variants have been studied at biochemical and biophysical levels. In this study we report on the functional and structural characterization of three naturally occurring variants corresponding to different classes of disease severity: Class I G6PD Durham, Class II G6PD Santa Maria, and Class III G6PD A+. The results showed that the G6PD Durham (severe deficiency), and the G6PD Santa Maria and A+ (less severe deficiency) (Class I, II and III, respectively) affect the catalytic efficiency of these enzymes, are more sensitive to temperature denaturing, and affect the stability of the overall protein when compared to the wild type WT-G6PD. In the variants, the exposure of more and buried hydrophobic pockets was induced and monitored with 8-Anilinonaphthalene-1-sulfonic acid (ANS) fluorescence, directly affecting the compaction of structure at different levels and probably reducing the stability of the protein. The degree of functional and structural perturbation by each variant correlates with the clinical severity reported in different patients.

The stability of G6PD is affected by mutations with different clinical phenotypes

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is the most common enzyme deficiency worldwide, causing a wide spectrum of conditions with severity classified from the mildest (Class IV) to the most severe (Class I). To correlate mutation sites in the G6PD with the resulting phenotypes, we studied four naturally occurring G6PD variants: Yucatan, Nashville, Valladolid and Mexico City. For this purpose, we developed a successful over-expression method that constitutes an easier and more precise method for obtaining and characterizing these enzymes. The k(cat) (catalytic constant) of all the studied variants was lower than in the wild-type. The structural rigidity might be the cause and the most evident consequence of the mutations is their impact on protein stability and folding, as can be observed from the protein yield, the T50 (temperature where 50% of its original activity is retained) values, and differences on hydrophobic regions. The mutations corresponding to more severe phenotypes are related to the structural NADP+ region. This was clearly observed for the Classes III and II variants, which became more thermostable with increasing NADP+, whereas the Class I variants remained thermolabile. The mutations produce repulsive electric charges that, in the case of the Yucatan variant, promote increased disorder of the C-terminus and consequently affect the binding of NADP+, leading to enzyme instability.

G6PD deficiency in Latin America: systematic review on prevalence and variants

Plasmodium vivax radical cure requires the use of primaquine (PQ), a drug that induces haemolysis in glucose-6-phosphate dehydrogenase deficient (G6PDd) individuals, which further hampers malaria control efforts. The aim of this work was to study the G6PDd prevalence and variants in Latin America (LA) and the Caribbean region. A systematic search of the published literature was undertaken in August 2013. Bibliographies of manuscripts were also searched and additional references were identified. Low prevalence rates of G6PDd were documented in Argentina, Bolivia, Mexico, Peru and Uruguay, but studies from Curaçao, Ecuador, Jamaica, Saint Lucia, Suriname and Trinidad, as well as some surveys carried out in areas of Brazil, Colombia and Cuba, have shown a high prevalence (> 10%) of G6PDd. The G6PD A-202A mutation was the variant most broadly distributed across LA and was identified in 81.1% of the deficient individuals surveyed. G6PDd is a frequent phenomenon in LA, although certain Amerindian populations may not be affected, suggesting that PQ could be safely used in these specific populations. Population-wide use of PQ as part of malaria elimination strategies in LA cannot be supported unless a rapid, accurate and field-deployable G6PDd diagnostic test is made available.

A novel point mutation in a class IV glucose-6-phosphate dehydrogenase variant (G6PD São Paulo) and polymorphic G6PD variants in São Paulo State, Brazil

In this study, we used red cell glucose-6-phosphate dehydrogenase (G6PD) activity to screen for G6PD-deficient individuals in 373 unrelated asymptomatic adult men who were working with insecticides (organophosphorus and carbamate) in dengue prevention programs in 27 cities in São Paulo State, Brazil. Twenty-one unrelated male children suspected of having erythroenzymopathy who were attended at hospitals in São Paulo city were also studied. Fifteen of the 373 adults and 12 of the 21 children were G6PD deficient. G6PD gene mutations were investigated in these G6PD-deficient individuals by using PCR-RFLP, PCR-SSCP analysis and DNA sequencing. Twelve G6PD A-202A/376G and two G6PD Seattle844C, as well as a new variant identified as G6PD São Paulo, were detected among adults, and 11 G6PD A-202A/376G and one G6PD Seattle844C were found among children. The novel mutation c.660C > G caused the replacement of isoleucine by methionine (I220M) in a region near the dimer interface of the molecule. The conservative nature of this mutation (substitution of a nonpolar aliphatic amino acid for another one) could explain why there was no corresponding change in the loss of G6PD activity (64.5% of normal activity in both cases).

Kernicterus by glucose-6-phosphate dehydrogenase deficiency: a case report and review of the literature

Introduction

Glucose-6-phosphate dehydrogenase deficiency is an X-linked recessive disease that causes acute or chronic hemolytic anemia and potentially leads to severe jaundice in response to oxidative agents. This deficiency is the most common human innate error of metabolism, affecting more than 400 million people worldwide.

Case presentation

Here, we present the first documented case of kernicterus in Panama, in a glucose-6-phosphate dehydrogenase-deficient newborn clothed in naphthalene-impregnated garments, resulting in reduced psychomotor development, neurosensory hypoacousia, absence of speech and poor reflex of the pupil to light.

Conclusion

Mutational analysis revealed the glucose-6-phosphate dehydrogenase Mediterranean polymorphic variant, which explained the development of kernicterus after exposition of naphthalene. As the use of naphthalene in stored clothes is a common practice, glucose-6-phosphate dehydrogenase testing in neonatal screening could prevent severe clinical consequences.

Glucose-6-phosphate dehydrogenase mutations in Mon and Burmese of southern Myanmar

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is highly prevalent in Southeast Asians. G6PD mutations are associated with specific ethnic groups in Southeast Asia. Mon is a minority ethnic group in Myanmar, which speaks Monic, a distinct language of Mon-Khmer classification. We studied G6PD mutations in Mon and Burmese males of southern Myanmar who migrated to Thailand in Samutsakhon province. G6PD deficiency was identified in 19 (12%) of 162 Mon males and 17 (10%) of 178 Burmese males, and then assayed for G6PD mutations. Among 19 G6PD-deficient Mons, 12 were G6PD Mahidol; one case each was G6PD Jammu (871G > A; nt 1311C), G6PD Kaiping (1388G > A), G6PD Mediterranean (563C > T), a novel mutation 94(C > G); and three remain unidentified. Among 17 G6PD-deficient Burmese, 12 were G6PD Mahidol; one each was G6PD Coimbra (592C > T), G6PD Kerala-Kalyan (949G > A), and G6PD Valladolid (406C > T); and two remain unidentified. G6PD Mahidol (487G > A) is the most common mutation among Mons and Burmese. All G6PD deficient Mon and Burmese, except for a person with G6PD Valladolid, shared the same haplotype nt93T, nt1311C. Despite a similar language root with Cambodian's Khmer language, our study suggests that Mon people share a common ancestry with Burmese rather than Cambodians.

G6PD (AC)n and (CTT)n microsatellites in Mexican Mestizos with common G6PD African variants

Genotyping for the G6PD (AC)n and (CTT)n microsatellites in a sample of 58 Mexican Mestizos with common G6PD African variants was carried out. The second mutation that defines to the variants G6PD A(-202A/376G), G6PD Santamaria(376G/542T) and G6PD A(-376G/968C) very probably occurred on G6PD A(376G) chromosomes with the compound haplotypes, intragenic silent polymorphisms and microsatellites, Pvu-II/Pst-I/Bcl-I/Nla-III/(AC)n/(CTT)n: +/+/-/+/166 bp/195 bp, -/+/-/+/166 bp/201 bp, and -/+/-/+/166 bp/204 bp respectively. The structure of the repeat sequences for the AC-166 bp allele in the 3 variants was (TA)5(AA)1(TA)9(CA)10 whereas the repeat sequences for the CTT-195 bp, CTT-201 bp and CTT-204 bp alleles were (CTT)11(ATT)6, (CTT)7(ATT)12 and (CTT)7(ATT)13 in the first, second and third variants respectively. Genotyping for the G6PD microsatellites can be a useful tool with several applications.