BACKGROUND: Glucose-6-phosphate dehydrogenase deficiency (G6PDd) has been shown 
to protect against malaria infection and severe manifestations in African and 
Asia, but there is a scarcity of studies in the Americas. This study aimed to 
study the prevalence of G6PDd and its association with malaria occurrence in the 
Brazilian Amazon.
METHODS: A cross-sectional study was conducted in the male population to 
estimate the prevalence of G6PDd and malaria infection. G6PD deficient samples 
were genotyped to identify the deficient variant. Number of previous malaria 
episodes and need for blood transfusion during malaria episodes were recorded by 
applying a standardized questionary.
RESULTS: From a sample of 1478 male individuals, 66 were detected as G6PD 
deficient, resulting in a prevalence of of 4.5% (95% CI = 3.44-5.56%). Fifty six 
G6PD deficient individuals (3.8%; 95% CI = 2.82-4.77) presented the G6PD 
A-variant mutation, while 10 individuals (0.7%; 95% CI = 0.42-0.97) severely 
deficient were genotyped as carriers of the G6PD Mediterranean variant. After 
adjusting for age, G6PD deficient individuals were less likely to report the 
occurrence of malaria episodes, and the protective effect was related to the 
enzyme activity, with carriers of the GG6PD A-variant presenting a 88% reduction 
(AOR: 0.119; 95% CI = 0.057-0.252; p < 0.001) and carriers of the Meditarrenean 
variant presenting 99% lower risk (AOR: 0.010; 95% CI = 0.002-0.252; p < 0.001) 
when compared to non-deficient individuals. On the other hand, G6PD deficient 
subjects reported higher need of transfusion during malaria episodes (p < 
0.001).
CONCLUSION: G6PD enzyme activity was directly related to susceptibility to 
malaria in the Brazilian Amazon, where P. vivax predominates. Severe G6PDd was 
associated with considerable higher risk of malaria-related transfusions.