Genetic heterogeneity at the glucose-6-phosphate dehydrogenase locus in southern Italy: a study on a population from the Matera district

Summary Glucose-6-phosphate dehydrogenase (G6PD) has been analyzed by gel electrophoresis and by quantitative assay in an unselected sample of 1524 schoolboys from the province of Matera (Lucania) in southern Italy. We have identified 43 subjects with a G6PD variant. Of these, 31 had severe G6PD deficiency, nine had mild to moderate deficiency, and three had a non-deficient electrophoretic variant. The overall rate of G6PD deficiency was 2.6%. The frequency of G6PD deficiency, ranging from 7.2% on the Ionian Coast to zero on the eastern side of the Lucanian Apennines, appears to be inversely related to the distance of each town examined from the Ionian Coast, suggesting that this geographic distribution may reflect, at least in part, gene flow from Greek settlers. Biochemical characterization has shown that most of the G6PD deficiency in this population is accounted for by G6PD Mediterranean. In addition, we have found several examples of two other known polymorphic variants (G6PD Cagliari and G6PD A^–): three new polymorphic variants. G6PD Metaponto (class III), G6PD Montalbano (class III), and G6PD Pisticci (class IV); and two sporadic variants, G6PD Tursi (class III) and G6PD Ferrandina (class II). These data provide further evidence for the marked genetic heterogeneity of G6PD deficiency within a relatively narrow geographic-area and they prove the presence in the Italian peninsula of a sene (Gd ^A–) regarded as characteristically African.     

Identification of glucose 6-phosphate dehydrogenase deficiency in a population with a high frequency of thalassemia

High frequencies of both thalassemia trait (5.2%) and glucose 6-phosphate dehydrogenase (G6PD) deficiency for only males (1.3%) have been observed in the Calabrian population. The G6PD activity measurement was carried out on 1239 samples of whole blood from Calabrian subjects of both sexes (age range 10-55) by a differential pH-metry technique which was quite suitable to determine the G6PD deficiency in mass screenings. The analyzed subjects showed: only the thalassemia trait; or only the G6PD deficiency; or only the total iron serum deficiency; or G6PD deficiency associated with the thalassemia trait or with the total iron serum deficiency. The G6PD heterozygous subjects have an enzymatic activity which is masked by both the thalassemia trait and the total iron serum deficiency. In a population showing high frequencies of both thalassemia trait and G6PD deficiency, the comparison of G6PD activity of heterozygous subjects also affected with the thalassemia trait is more reliable if referred to the enzymatic activity of the carriers of the latter inherited anomaly rather than to G6PD activity of normal subjects.     

Two point mutations are responsible for G6PD polymorphism in Sardinia.

The human X-linked gene encoding glucose 6-phosphate dehydrogenase (G6PD) is highly polymorphic; more than 300 G6PD variants have been identified. G6PD deficiency in different geographical areas appears to have arisen through independent mutational events, but within the same population it may also be heterogeneous. One example is the island of Sardinia, where careful clinical and biochemical studies have identified four different G6PD variants. We cloned and sequenced the four G6PD variants from Sardinia and found that only two mutations are responsible for G6PD deficiency in this area: one mutation is the cause of the G6PD Seattle-like phenotype, a milder form of G6PD deficiency; the other mutation is responsible for all forms of very severe G6PD deficiency in Sardinia and, possibly, in the Mediterranean.     

G6PD-MutDB: a mutation and phenotype database of glucose-6-phosphate (G6PD) deficiency

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is the most common hereditary enzymatic disorder of red blood cells in humans due to mutations in the G6PD gene. The G6PD enzyme catalyzes the first step in the pentose phosphate pathway to protect cells against oxidative stress. Mutations in the G6PD gene will cause functional variants with various biochemical and clinical phenotypes. So far, about 160 mutations along with more than 400 biochemical variants have been described. G6PD-MutDB is a disease-specific resource of G6PD deficiency, collecting and integrating G6PD mutations with biochemical and clinical phenotypes. Data of G6PD deficiency is manually extracted from published papers, focusing primarily on variants with identified mutation and well-described quantitative phenotypes. G6PD-MutDB implements an approach, CNSHA predictor, to help identify a potential chronic non-spherocytic hemolytic anemia (CNSHA) phenotype of an unknown mutation. G6PD-MutDB is believed to facilitate analysis of relationship between molecular mutation and functional phenotype of G6PD deficiency owing to convenient data resource and useful tools. This database is available from http://202.120.189.88/mutdb.     

Large Cohort Screening of G6PD Deficiency and the Mutational Spectrum in the Dongguan District in Southern China

Background

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is a common enzymatic disorder of the erythrocytes that affects 400 million people worldwide. We developed a PCR-reverse dot blot (RDB) assay to screen twenty genotypes of seventeen Chinese G6PD mutations and investigate the spectrum of G6PD deficiency mutations in Dongguan District, Guangdong Province, in southern China.

Method

The PCR-RDB assay consists of multiplex PCR amplification of seven fragments in the G6PD target sequence of wild-type and mutant genomic DNA samples followed by hybridization to a test strip containing allele-specific oligonucleotide probes. A total of 16,464 individuals were analyzed by a combination of phenotypic screening and genotypic detection using the PCR-RDB assay and DNA sequence analysis.

Results

The PCR-RDB assay had a detection rate of 98.1%, which was validated by direct sequencing in a blind study with 100% concordance. The G6PD deficiency incidence rate in Dongguan District is 4.08%. Thirty-two genotypes from 469 individuals were found. The two most common variants were c.1376G>T and c.1388G>A, followed by c.95A>G, c.871G>A, c.392G>T, and c.1024 C>T. In addition, two rare mutations (c.703C>A and c.406C>T) were detected by DNA sequencing analysis. In our study, 65 cases harbored the C1311T/IVS polymorphism and 67 cases were homozygote.

Conclusion

The PCR-RDB assay we established is a reliable and effective method for screening G6PD mutations in the Chinese population. Data on the spectrum of mutations in the Dongguan District is beneficial to the clinical diagnosis and prevention of G6PD deficiency.     

Some Mexican glucose-6-phosphate dehydrogenase variants revisited

Summary Glucose-6-phosphate dehydrogenase (G6PD) deficiency appears to be fairly common in Mexico. We have now examined the DNA of three previously reported electrophoretically fast Mexican G6PD variants, — G6PD Distrito Federal, G6PD Tepic, and G6PD Castilla. All three of these variants, believed on the basis of biochemical characterization and population origin to be unique, have the GA transition at nucleotide 202 and the AG transition at nucleotide 376, mutations that we now recognize to be characteristic of G6PD A —. Two other Mexican males with G6PD deficiency were found to have the same mutation. All five have the (NlaIII/ FokI/PvuII/PstI) haplotype characteristic of G6PD A in Africa. Since the PvuII+ genotype seems to be rare in Europe, we conclude that all of these G6PD A-genes had their ancient origin in Africa, although in many of the Mexican patients with G6PD A –^202A/376G the gene may have been imported more recently from Spain, where this variant, formerly known as G6PD Betica, is also prevalent.     

Glucose-6-phosphate dehydrogenase deficiency in Saudi Arabia. A study in Al-Ula

This paper reports the frequency of glucose-6-phosphate dehydrogenase (G6PD) deficiency in the male and female population of A1-Ula in the northwestern province of Saudi Arabia. The frequency of G6PD deficiency in the male population was 0.098 and in the females it was 0.028. This frequency is significantly lower than those reported for other malaria endemic regions in Arabia. The population was further subgrouped on the basis of their haemoglobin phenotypes and the highest frequency of G6PD deficiency was obtained in male Hb S heterozygotes followed by the male Hb S homozygotes. Phenotyping of G6PD revealed the presence of G6PD-Mediterranean, G6PDA+, G6PDA- and G6PD Mediterranean-like, and the frequency of these variants in Al-Ula was different from those reported in other regions of Saudi Arabia.     

Characterization of G6PD Genotypes and Phenotypes on the Northwestern Thailand-Myanmar Border

Mutations in the glucose-6-phosphate dehydrogenase (G6PD) gene result in red blood cells with increased susceptibility to oxidative damage. Significant haemolysis can be caused by primaquine and other 8-aminoquinoline antimalarials used for the radical treatment of Plasmodium vivax malaria. The distribution and phenotypes of mutations causing G6PD deficiency in the male population of migrants and refugees in a malaria endemic region on the Thailand-Myanmar border were characterized. Blood samples for G6PD fluorescent spot test (FST), G6PD genotyping, and malaria testing were taken from 504 unrelated males of Karen and Burman ethnicities presenting to the outpatient clinics. The overall frequency of G6PD deficiency by the FST was 13.7%. Among the deficient subjects, almost 90% had the Mahidol variant (487G>A) genotype. The remaining subjects had Chinese-4 (392G>T), Viangchan (871G>A), Açores (595A>G), Seattle (844G>C) and Mediterranean (563C>T) variants. Quantification of G6PD activity was performed using a modification of the standard spectrophotometric assay on a subset of 24 samples with Mahidol, Viangchan, Seattle and Chinese-4 mutations; all samples showed a residual enzymatic activity below 10% of normal and were diagnosed correctly by the FST. Further studies are needed to characterise the haemolytic risk of using 8-aminoquinolines in patients with these genotypes.     

Distribution of glucose-6-phosphate dehydrogenase mutations in Southeast Asia

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is a heterogeneous enzyme abnormality with high frequency in tropical areas. We performed population screening and molecular studies of G6PD variants to clarify their distribution and features in Southeast Asia. A total of 4317 participants (2019 males, 2298 females) from 16 ethnic groups in Myanmar, Lao in Laos, and Amboinese in Indonesia were screened with a single-step screening method. The prevalence of G6PD-deficient males ranged from 0% (the Akha) to 10.8% (the Shan). These G6PD-deficient individuals and 12 G6PD-deficient patients who had been diagnosed at hospitals in Indonesia and Malaysia were subjected to molecular analysis by a combination of polymerase-chain-reaction-based single-strand conformation polymorphism analysis and direct sequencing. Ten different missense mutations were identified in 63 G6PD-deficient individuals (50 hemizygotes, 11 heterozygotes, and 2 homozygotes) from 14 ethnic groups. One missense mutation (1291 G-->A) found in an Indonesian Chinese, viz., G6PD Surabaya, was previously unknown. The 487 G-->A (G6PD Mahidol) mutation was widely seen in Myanmar, 383 T-->C (G6PD Vanua Lava) was specifically found among Amboinese, 871 G-->A (G6PD Viangchan) was observed mainly in Lao, and 592 C-->T (G6PD Coimbra) was found in Malaysian aborigines (Orang Asli). The other five mutations, 95 A-->G (G6PD Gaohe), 1003 G-->A (G6PD Chatham), 1360 C-->T (G6PD Union), 1376 G-->T (G6PD Canton), and 1388 G-->A (G6PD Kaiping) were identified mostly in accordance with distributions reported previously.     

Prevalence and Molecular Characterization of Glucose-6-Phosphate Dehydrogenase Deficiency at the China-Myanmar Border

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is an X-linked hereditary disease that predisposes red blood cells to oxidative damage. G6PD deficiency is particularly prevalent in historically malaria-endemic areas. Use of primaquine for malaria treatment may result in severe hemolysis in G6PD deficient patients. In this study, we systematically evaluated the prevalence of G6PD deficiency in the Kachin (Jingpo) ethnic group along the China-Myanmar border and determined the underlying G6PD genotypes. We surveyed G6PD deficiency in 1770 adult individuals (671 males and 1099 females) of the Kachin ethnicity using a G6PD fluorescent spot test. The overall prevalence of G6PD deficiency in the study population was 29.6% (523/1770), among which 27.9% and 30.6% were males and females, respectively. From these G6PD deficient samples, 198 unrelated individuals (147 females and 51 males) were selected for genotyping at 11 known G6PD single nucleotide polymorphisms (SNPs) in Southeast Asia (ten in exons and one in intron 11) using a multiplex SNaPshot assay. Mutations with known association to a deficient phenotype were detected in 43.9% (87/198) of cases, intronic and synonymous mutations were detected alone in 34.8% (69/198) cases and no mutation were found in 21.2% (42/198) cases. Five non-synonymous mutations, Mahidol 487G>A, Kaiping 1388G>A, Canton 1376G>T, Chinese 4 392G>T, and Viangchan 871G>A were detected. Of the 87 cases with known deficient mutations, the Mahidol variant was the most common (89.7%; 78/87), followed by the Kaiping (8.0%; 7/87) and the Viangchan (2.2%; 2/87) variants. The Canton and Chinese 4 variants were found in 1.1% of these 87 cases. Among them, two females carried the Mahidol/Viangchan and Mahidol/Kaiping double mutations, respectively. Interestingly, the silent SNPs 1311C>T and IVS11nt93T>C both occurred in the same 95 subjects with frequencies at 56.4% and 23.5% in tested females and males, respectively (P<0.05). It is noteworthy that 24 subjects carrying the Mahidol mutation and two carrying the Kaiping mutation also carried the 1311C>T/IVS11nt93T>C SNPs. Further studies are needed to determine the enzyme levels of the G6PD deficient people and presence of additional G6PD mutations in the study population.     

Variants of glucose-6-phosphate dehydrogenase in a Vietnamese population

69 out of 2,304 Vietnamese males were found to be hemizygous carriers of the Gd- gene. The glucose-6-phosphate dehydrogenase (G6PD) deficiency had a polymorphic frequency in the Vietnamese population (0.0299). Genetic heterogeneity in G6PD was found - 3 G6PD variants were found among 13 G6PD-deficient males studied (G6PD Canton, G6PD Hanoi and G6PD Vin Fu). Two new variants were identified - G6PD Hanoi and G6PD Vin Fu.     

African Glucose-6-Phosphate Dehydrogenase Alleles Associated with Protection from Severe Malaria in Heterozygous Females in Tanzania

X-linked Glucose-6-phosphate dehydrogenase (G6PD) A- deficiency is prevalent in sub-Saharan Africa populations, and has been associated with protection from severe malaria. Whether females and/or males are protected by G6PD deficiency is uncertain, due in part to G6PD and malaria phenotypic complexity and misclassification. Almost all large association studies have genotyped a limited number of G6PD SNPs (e.g. G6PD202 / G6PD376), and this approach has been too blunt to capture the complete epidemiological picture. Here we have identified 68 G6PD polymorphisms and analysed 29 of these (i.e. those with a minor allele frequency greater than 1%) in 983 severe malaria cases and controls in Tanzania. We establish, across a number of SNPs including G6PD376, that only female heterozygotes are protected from severe malaria. Haplotype analysis reveals the G6PD locus to be under balancing selection, suggesting a mechanism of protection relying on alleles at modest frequency and avoiding fixation, where protection provided by G6PD deficiency against severe malaria is offset by increased risk of life-threatening complications. Our study also demonstrates that the much-needed large-scale studies of severe malaria and G6PD enzymatic function across African populations require the identification and analysis of the full repertoire of G6PD genetic markers.     

Two commonly occurring nucleotide base substitutions in Chinese G6PD variants

Using a direct PCR sequencing technique, we have identified two DNA base substitutions in 8 different biochemical G6PD variants of Chinese origin. Neither one of these abnormalities has been reported in other ethnic groups. An abnormality (C1) of G to T substitution at cDNA 1376 causing an amino acid change from Arg to Leu has been found in 3 variants. Another abnormality (C2) of G to A substitution at cDNA 1388 causing an amino acid change from Arg to His has been found in 5 variants. Both C1 and C2 are located in exon 12 of the G6PD gene and are only 12 base pairs apart. However, C1 is associated with a significant increase in the deamino-NADP utilization rate, whereas C2 is not. Taken together, our data suggest that C1 and C2 are very common among Chinese with a G6PD deficiency and exon 12 may define an important functional domain of the human G6PD.     

Functional hemizygosity in the human genome: direct estimate from twelve erythrocyte enzyme loci

Summary Cord blood samples from 2020 unrelated newborns were screened for levels of enzyme activity for twelve enzymes. The level of enzymatic activity for 100 determinations were consistent with the existence of an enzyme-deficiency allele. The frequency of deficiency alleles in the Black population (0.0071) was four times higher (after removal of the G6PD^*A^- variant) than in the Caucasian sample (0.0016). These frequencies are approximately double the frequency of rare electrophoretic mobility variants at similar loci in the same population. Given the number of functionally important loci in the human genome, these enzyme deficiency variants could constitute a significant health burden.     

Performance of the CareStart? G6PD Deficiency Screening Test,a Point-of-Care Diagnostic for Primaquine Therapy Screening

Development of reliable, easy-to-use, rapid diagnostic tests (RDTs) to detect glucose-6-phosphate dehydrogenase (G6PD) deficiency at point of care is essential to deploying primaquine therapies as part of malaria elimination strategies. We assessed a kit under research and development called CareStart™ G6PD deficiency screening test (Access Bio, New Jersey, USA) by comparing its performance to quantitative G6PD enzyme activity using a standardized spectrophotometric method (‘gold standard’). Blood samples (n = 903) were collected from Cambodian adults living in Pailin province, western Cambodia. G6PD enzyme activities ranged from 0 to 20.5 U/g Hb (median 12.0 U/g Hg). Based on a normal haemoglobin concentration and wild-type G6PD gene, the normal values of G6PD enzymatic activity for this population was 3.6 to 20.5 U/g Hg (95^th percentiles from 5.5 to 17.2 U/g Hg). Ninety-seven subjects (10.7%) had <3.6 U/g Hg and were classified as G6PD deficient. Prevalence of deficiency was 15.0% (64/425) among men and 6.9% (33/478) among women. Genotype was analyzed in 66 G6PD-deficient subjects and 63 of these exhibited findings consistent with Viangchang genotype. The sensitivity and specificity of the CareStart™ G6PD deficiency screening test was 0.68 and 1.0, respectively. Its detection threshold was <2.7 U/g Hg, well within the range of moderate and severe enzyme deficiencies. Thirteen subjects (1.4%, 12 males and 1 female) with G6PD enzyme activities <2 U/g Hg were falsely classified as “normal” by RDT. This experimental RDT test here evaluated outside of the laboratory for the first time shows real promise, but safe application of it will require lower rates of falsely “normal” results.     

Molecular heterogeneity of the glucose-6-phosphate dehydrogenase deficiency in the Hellenic population

We report results from a systematic study to identify the molecular basis of glucose-6-phosphate dehydrogenase (G6PD) deficiency on a sample of 299 male subjects from the Hellenic population. Our stepwise approach involved partial biochemical characterization and quantitation of the enzyme's activity, MboII restriction endonuclease digestion to identify the G6PD Mediterranean variant, which represents the most frequent G6PD variant in our population and a nonradioactive polymerase chain reaction-single-strand conformation polymorphism methodology for the detection of the underlying molecular defect(s) in the rest of the non-Mediterranean G6PD-deficient individuals. Through this approach, six different G6PD variants were identified (G6PD Mediterranean, G6PD Hermoupolis, G6PD Cassano, G6PD Seattle, G6PD Ierapetra and G6PD Acrokorinthos), two of which were new (G6PD Hermoupolis, G6PD Acrokorinthos). In essence, this study underlines the remarkable genetic heterogeneity of the G6PD deficiency in the Hellenic population, while the finding of the double mutant, G6PD Hermoupolis, may help to outline the relationship and evolution of mutations in the human G6PD locus.     

Genetic heterogeneity at the glucose-6-phosphate dehydrogenase locus in southern Italy: a study on the population of Naples

Summary Glucose-6-phosphate dehydrogenase (G6PD) electrophoretic phenotype was determined in red cells from 979 male subjects born in Naples (Southern Italy). In 0.7% of the cases no activity could be detected in haemolysates, while in 1.3% of the cases G6PD activity was approximately 20% of normal and electrophoretic mobility was altered. Moveover in two subjects a G6PD with altered mobility and normal activity was shown. G6PD was characterized in 10 subjects with variant phenotype. We conclude that the G6PD(-) phenotype in the population of Naples consists of at least six different G6PD variants associated with mild deficiency and at least one, G6PD Mediterranean, associated with severe deficiency.     

Heterogeneity of glucose-6-phosphate dehydrogenase deficiency in Algeria

Summary Glucose-6-phosphate dehydrogenase (G6PD) deficiency was found in 3.2% of the male population living in the urban area of Algiers. The deficient subjects originated from multiple geographic regions of Northern Algeria, with prevalence of individuals of Berber-Kabyle origin. Red blood cell G6PD was partially purified and characterized in deficient males from 17 families, and six different variants were found. Among them, only one, the Gd(-) Kabyle variant, had been previously described. It was detected in nine families. The other five variants were new: Gd(-) Laghouat (four cases), Gd(-) Blida (one case), Gd(-) Thenia (one case), Gd(-) Titteri (one case), and Gd(-) Alger (two brothers), Strikingly, the common Mediterranean variant was not found. G6PD deficiency is heterogeneous in northern Algeria where autochtonous variants seem to prevail. The Kabyle variant may be common in this country.     

G6PD lozere and trinacria-like

Summary Two new G6PD variants have been found in red blood cells of the members of a French family originating from Lozere. The father is hemizygous for an electrophoretically fast variant with mild enzyme deficiency (50–60% of normal). The abnormal paternal G6PD gene is segregating in his daughter who is double heterozygous for maternal and paternal variants. This mutant enzyme, different from previously described variants is designated as Gd Lozère. The mother is heterozygous for another G6PD variant. Two sons are hemizygous for this latter mutant enzyme characterized by a moderate deficiency (25–30% of normal) and slower electrophoretic mobility with some slightly altered kinetic properties. This G6PD has been identified as Gd Trinacria like.These two abnormal enzymes are not associated with any hemolytic problem. Case reported is the first showing the segregation of two new mutant enzymes, distinct from common G6PD variants, among the members of the same family.