tokens: From the alignment of the amino acid ( aa ) sequence of 52 glucose 6 - phosphate dehydrogenase ( G6PD ) species from 42 different organisms , we found a striking correlation between the aa replacements that cause G6PD deficiency in humans and the sequence conservation of G6PD two - thirds of such replacements are in highly and moderately conserved ( 50 - 99 % ) aa ; relatively few are in fully conserved aa ( where they might be lethal ) or in poorly conserved aa , where presumably they simply would not cause G6PD deficiency .