[Gene point mutation in the dihydrofolate reductase-thymidylate synthase gene of Plasmodium falciparum].

Objective: To investigate the gene point mutation in the dihydrofolate reductase-thymidylate synthase(dhfr) gene of Plasmodium falciparum isolate from Yunnan Province strongly associated with pyrimethamine and cycloguanil resistance.
Methods: Nested PCR and restriction endonuclease digestion were applied to detect the gene mutation using dried blood filter paper collected from the fields in Yunnan Province.
Results: Different mutations were found in 4 amino acids at positions 16, 51, 108 and 164 of dhfr gene, particularly, Asn-108 and Ile-51, the mutation frequency being 94.1% and 90.1%, respectively. The frequency of the wild-type genotype (3D7-type) Ser-108 appeared lower (9.1%), while the frequency of the Ala-16 was high(61.8%); the mutation-type was very high, the ratio of HB3-type, 7G8-type/FCR3-type and Cambodian-type was 1:21:7.5.
Conclusion: The investigation first demonstrated that Plasmodium falciparum Yunnan isolate dihydrofolate reductase-thymidylate synthase gene (dhfr) at positions 16, 51, 108 and 164 exhibited different degrees of point mutation. The frequency of mutation of the 7D8-type involved in pyrimethamine resistance was higher, while that of the FCR3-type involved in cycloquanil resistance was lower.