The distribution of G6PD-D in the Ferrara country has been studied by means of the Brilliant Cresyl Blue discoloration test: 2437 males have been tested in 11 localities.
The highest gene frequency of G6PD-D observed is consistent with the one expected after 25-30 generations of malaria selection, assuming an increased fitness of the heterozygotes, as it has been shown in computer simulated evolutionary trends for sex-linked genes. The thalassemia trait has also been shown to be very frequent in the same localities; its frequency is correlated with G6PD-D gene frequency and with the incidence of malaria in the past (1900).
G6PD-D frequency is not significantly correlated with malaria. Such a result is due to the significantly lower gene frequency of G6PD-D observed in the localities where the percentage of population affected by malaria was higher (40-60%). On the other hand, G6PD-D is frequently significantly correlated with malaria in the remaining localities where the incidence of the latter ranged from 0 to 35% of the affected population.
The mechanisms possibly involved in the determination of this distribution of G6PD-D are discussed.