Examining the relationship between genetic variation at G6PD and severe malaria

Glucose-6-phosphate dehydrogenase (G6PD) deficiency, a common heritable trait whose prevalence mirrors geographic patterns of historic malaria endemicity, is thought to confer a selective advantage owing to partial protection conferred against malaria. Direct evidence supporting this malaria protection hypothesis in the form of clinical association studies remains controversial, however, as conflicting results have been reported with respect to the strength and specificity of a protective effect, if any, conferred to carriers of G6PD deficiency-associated alleles.This thesis examines genetic diversity at the G6PD locus, and then considers how such variation impacts both immediate molecular phenotypes and multifactorial clinical phenotypes. First, Chapter 3 presents a survey of variation at G6PD in several malaria-endemic areas, while Chapter 4 describes a novel technique for polymorphism discovery using pooled massively parallel sequencing. Next, in Chapters 5 and 6, I evaluate the link between genetic variation at the locus and G6PD enzyme activity, identifying major and minor determinants of G6PD deficiency state in an association study conducted in Kenya, and demonstrating a new technique for assaying G6PD deficiency at the level of an individual erythrocyte in a pilot project in Mali. Finally, Chapter 7 addresses the malaria protection hypothesis directly by conducting a fine-mapping case-control association study of severe malaria in the Gambia, where I found that G6PD deficiency alleles exhibited differential direction of association with respect to two important clinical syndromes-- trending towards risk conferred to severe malarial anemia, and protection with respect to cerebral malaria. Overall, these findings suggest that future clinical association studies should consider heterogeneity at the genetic level, as well as at the level of molecular and clinical phenotypes in order to achieve a better mechanistic understanding of the relationship between G6PD deficiency and severe malaria.