Genotype-phenotype association and biochemical analyses of glucose-6-phosphate dehydrogenase variants: Implications for the hemolytic risk of using 8-aminoquinolines for radical cure

Improved genetic screening with zygosity detection through multiplex high-resolution melting curve analysis and biochemical characterisation for G6PD deficiency

Accurate diagnosis of glucose-6-phosphate dehydrogenase (G6PD) deficiency is crucial for relapse malaria treatment using 8-aminoquinolines (primaquine and tafenoquine), which can trigger haemolytic anaemia in G6PD-deficient individuals. This is particularly important in regions where the prevalence of G6PD deficiency exceeds 3%-5%, including Southeast Asia and Thailand. While quantitative phenotypic tests can identify women with intermediate activity who may be at risk, they cannot unambiguously identify heterozygous females who require appropriate counselling. This study aimed to develop a genetic test for G6PD deficiency using high-resolution melting curve analysis, which enables zygosity identification of 15 G6PD alleles. In 557 samples collected from four locations in Thailand, the prevalence of G6PD deficiency based on indirect enzyme assay was 6.10%, with 8.08% exhibiting intermediate deficiency. The developed high-resolution melting assays demonstrated excellent performance, achieving 100% sensitivity and specificity in detecting G6PD alleles compared with Sanger sequencing. Genotypic variations were observed across four geographic locations, with the combination of c.1311C>T and c.1365-13T>C being the most common genotype. Compound mutations, notably G6PD Viangchan (c.871G>A, c.1311C>T and c.1365-13T>C), accounted for 15.26% of detected mutations. The high-resolution melting assays also identified the double mutation G6PD Chinese-4 + Canton and G6PD Radlowo, a variant found for the first time in Thailand. Biochemical and structural characterisation revealed that these variants significantly reduced catalytic activity by destabilising protein structure, particularly in the case of the Radlowo mutation. The refinement of these high-resolution melting assays presents a highly accurate and high-throughput platform that can improve patient care by enabling precise diagnosis, supporting genetic counselling and guiding public health efforts to manage G6PD deficiency-especially crucial in malaria-endemic regions where 8-aminoquinoline therapies pose a risk to deficient individuals.

Genetic analysis and molecular basis of G6PD deficiency among malaria patients in Thailand: implications for safe use of 8-aminoquinolines

BACKGROUND

It was hypothesized that glucose-6-phosphate dehydrogenase (G6PD) deficiency confers a protective effect against malaria infection, however, safety concerns have been raised regarding haemolytic toxicity caused by radical cure with 8-aminoquinolines in G6PD-deficient individuals. Malaria elimination and control are also complicated by the high prevalence of G6PD deficiency in malaria-endemic areas. Hence, accurate identification of G6PD deficiency is required to identify those who are eligible for malaria treatment using 8-aminoquinolines.

METHODS

The prevalence of G6PD deficiency among 408 Thai participants diagnosed with malaria by microscopy (71), and malaria-negative controls (337), was assessed using a phenotypic test based on water-soluble tetrazolium salts. High-resolution melting (HRM) curve analysis was developed from a previous study to enable the detection of 15 common missense, synonymous and intronic G6PD mutations in Asian populations. The identified mutations were subjected to biochemical and structural characterisation to understand the molecular mechanisms underlying enzyme deficiency.

RESULTS

Based on phenotypic testing, the prevalence of G6PD deficiency (< 30% activity) was 6.13% (25/408) and intermediate deficiency (30-70% activity) was found in 15.20% (62/408) of participants. Several G6PD genotypes with newly discovered double missense variants were identified by HRM assays, including G6PD Gaohe + Viangchan, G6PD Valladolid + Viangchan and G6PD Canton + Viangchan. A significantly high frequency of synonymous (c.1311C>T) and intronic (c.1365-13T>C and c.486-34delT) mutations was detected with intermediate to normal enzyme activity. The double missense mutations were less catalytically active than their corresponding single missense mutations, resulting in severe enzyme deficiency. While the mutations had a minor effect on binding affinity, structural instability was a key contributor to the enzyme deficiency observed in G6PD-deficient individuals.

CONCLUSIONS

With varying degrees of enzyme deficiency, G6PD genotyping can be used as a complement to phenotypic screening to identify those who are eligible for 8-aminoquinolines. The information gained from this study could be useful for management and treatment of malaria, as well as for the prevention of unanticipated reactions to certain medications and foods in the studied population.

Molecular characterization of G6PD mutations identifies new mutations and a high frequency of intronic variants in Thai females

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is an X-linked enzymopathy caused by mutations in the G6PD gene. A medical concern associated with G6PD deficiency is acute hemolytic anemia induced by certain foods, drugs, and infections. Although phenotypic tests can correctly identify hemizygous males, as well as homozygous and compound heterozygous females, heterozygous females with a wide range of G6PD activity may be misclassified as normal. This study aimed to develop multiplex high-resolution melting (HRM) analyses to enable the accurate detection of G6PD mutations, especially among females with heterozygous deficiency. Multiplex HRM assays were developed to detect six G6PD variants, i.e., G6PD Gaohe (c.95A>G), G6PD Chinese-4 (c.392G>T), G6PD Mahidol (c.487G>A), G6PD Viangchan (c.871G>A), G6PD Chinese-5 (c.1024C>T), and G6PD Union (c.1360C>T) in two reactions. The assays were validated and then applied to genotype G6PD mutations in 248 Thai females. The sensitivity of the HRM assays developed was 100% [95% confidence interval (CI): 94.40%-100%] with a specificity of 100% (95% CI: 88.78%-100%) for detecting these six mutations. The prevalence of G6PD deficiency was estimated as 3.63% (9/248) for G6PD deficiency and 31.05% (77/248) for intermediate deficiency by phenotypic assay. The developed HRM assays identified three participants with normal enzyme activity as heterozygous for G6PD Viangchan. Interestingly, a deletion in intron 5 nucleotide position 637/638 (c.486-34delT) was also detected by the developed HRM assays. G6PD genotyping revealed a total of 12 G6PD genotypes, with a high prevalence of intronic variants. Our results suggested that HRM analysis-based genotyping is a simple and reliable approach for detecting G6PD mutations, and could be used to prevent the misdiagnosis of heterozygous females by phenotypic assay. This study also sheds light on the possibility of overlooking intronic variants, which could affect G6PD expression and contribute to enzyme deficiency.

Genomic Sequencing as a First-Tier Screening Test and Outcomes of Newborn Screening

Importance

Newborn screening via biochemical tests is in use worldwide. The availability of genetic sequencing has allowed rapid screening for a substantial number of monogenic disorders. However, the outcomes of this strategy have not been evaluated in a general newborn population.

Objective

To evaluate the outcomes of applying gene panel sequencing as a first-tier newborn screening test.

Design, Setting, and Participants

This cohort study included newborns who were prospectively recruited from 8 screening centers in China between February 21 and December 31, 2021. Neonates with positive results were followed up before July 5, 2022.

Exposures

All participants were concurrently screened using dried blood spots. The screen consisted of biochemical screening tests and a targeted gene panel sequencing test for 128 conditions. The biochemical and genomic tests could both detect 43 of the conditions, whereas the other 85 conditions were screened solely by the gene panel.

Main Outcomes and Measures

The primary outcomes were the number of patients detected by gene panel sequencing but undetected by the biochemical test.

Results

This study prospectively recruited 29 601 newborns (15 357 [51.2%] male). The mean (SD) gestational age was 39.0 (1.5) weeks, and the mean (SD) birth weight was 3273 (457) g. The gene panel sequencing screened 813 infants (2.7%; 95% CI, 2.6%-2.9%) as positive. By the date of follow-up, 402 infants (1.4%; 95% CI, 1.2%-1.5%) had been diagnosed, indicating the positive predictive value was 50.4% (95% CI, 50.0%-53.9%). The gene panel sequencing identified 59 patients undetected by biochemical tests, including 20 patients affected by biochemically and genetically screened disorders and 39 patients affected by solely genetically screened disorders, which translates into 1 out of every 500 newborns (95% CI, 1/385-1/625) benefiting from the implementation of gene panels as a first-tier screening test.

Conclusions and Relevance

In this cohort study, the use of gene panel sequencing in a general newborn population as a first-tier screening test improved the detection capability of traditional screening, providing an evidence-based suggestion that it could be considered as a crucial method for first-tier screening.