886 locus is most closely related to the relapse of vivax malaria and CYP2D6*2 allele containing this mutation locus was significantly higher in SR; and (3) The *4/*4 genotype that indicates null CYP2D6 enzyme function (poor metabolizers) was only found in the SR cases. The gene discussed is CYP2D6; the disease is Plasmodium vivax malaria.