Plasmodium vivax dihydrofolate reductase point mutations from the Indian subcontinent.

Mutations in Dihydrofolate Reductase (dhfr) gene of Plasmodium vivax are known to be associated with resistance to antifolate drugs. To analyze the extent of these mutations in P. vivax population in India, dhfr gene was isolated and sequenced for 121 P. vivax isolates originating from different geographical regions of Indian subcontinent. These sequences were compared with the gene sequence that represent wild type sequence (accession no. X98123). P. vivax dhfr (Pvdhfr) sequences showed limited polymorphism and about 70% isolates showed wild type dhfr sequence. A total of 36 mutations were found at 11 positions in 121 isolates. A majority of mutant isolates showed double mutations at residues 58 (S-->R) and 117 (S-->N), known to be associated with pyrimethamine resistance, but only 19% showed double mutations at residues 57 (F-->L) and 58 (S-->R). Pvdhfr alleles showing quadruple mutation (F57L, S58R, T61M and S117T) were found in two isolates. Three other mutations reported earlier at residue 13, 33 and 173 were not found in any of the Isolates. Six novel mutations at residues 38 (R-->G), 93 (S-->C), 109 (S-->H), 131 (R-->G), 159 (V-->A) and 188 (I-->V) were observed in seven isolates. Whether these novel mutations are linked to pyrimethamine resistance remains to be established.