Wide variation in microsatellite sequences within each Pfcrt mutant haplotype

Area of Science:

• Molecular Parasitology
• Genetics
• Malariology

Background:

• The Pfcrt gene is a key determinant of chloroquine resistance in Plasmodium falciparum.
• Microsatellites flanking the Pfcrt gene are generally conserved across geographical isolates.
• Intragenic microsatellite diversity within the Pfcrt gene has not been extensively studied.

Purpose of the Study:

• To investigate the heterogeneity of intragenic microsatellites within the Pfcrt gene in Plasmodium falciparum isolates.
• To determine the diversity of microsatellite genotypes associated with different Pfcrt haplotypes.
• To assess the implications of microsatellite variation for understanding chloroquine resistance in India.

Main Methods:

• Analysis of AT and TA repeat microsatellites in introns 2 and 4 of the Pfcrt gene.
• Genotyping of 224 Plasmodium falciparum isolates from India.
• Comparison of microsatellite genotypes with known Pfcrt haplotypes and geographical origins.

Main Results:

• Significant heterogeneity was observed in intragenic microsatellites (14 AT alleles, 8 TA alleles).
• 33 distinct two-locus microsatellite genotypes were identified among 224 Indian isolates.
• Indian isolates shared microsatellite genotypes with Southeast Asian P. falciparum lines but not with South American lines.
• Increased microsatellite variation was noted in areas of high malaria transmission over a 2-year period.

Conclusions:

• Genetic recombination in intragenic microsatellites of Pfcrt persists in Plasmodium falciparum populations.
• The diverse Pfcrt haplotypes and intragenic microsatellite genotypes indicate a broad spectrum of chloroquine resistance in India.
• This genetic diversity information is crucial for effective malaria control strategies in India.