Epidemiology of G6PD deficiency. The map was constructed by compiling, from the world literature, data on the population frequency of polymorphic G6PD alleles that cause enzyme deficiency. Country-specific frequency ranges, full references, and additional details are given in supplemental Table 1, available on the Blood Web site. Although frequencies may vary widely within the same country, each country was assigned here a color based on the best estimate of the average frequency of G6PD deficiency, probably the most important figure from the point of view of public health. This map represents a thorough update of one first published in 1989 and widely reproduced.²⁰  A similar map was published in 2009,²¹  and one based on a sophisticated geostatistical model in 2012.²²