Analysis of kappa and omega repeats of the cg2 gene and chloroquine susceptibility in isolates of Plasmodium fulciparum from sub-Saharan Africa

The correlation between the structure of two short sequences from the Plasm odium falciparum cg2 gene and parasite chloroquine susceptibility was evalu ated in unselected clinical isolates obtained from travellers returning mai nly from Africa to France in 1995 and 1996. As determined by an isotopic se mi-microtest, 74 isolates were susceptible to chloroquine (50% inhibitory c oncentration < 80 nM), 13 were intermediate (80 nM < 50% inhibitory concent ration < 110 nM) and 53 were resistant (50% inhibitory concentration > 110 nM). Two polymerase chain reaction assays were developed, one for the kappa and one for the omega repeat domains of cg2 gene. The kappa and the omega repeal domains of 99 isolates were sequenced. A variation in the unit numbe r of kappa and omega repeats was observed. Variations in repetitive sequenc es, which were not previously described, were found: three for the kappa re peat region: kappa 9; kappa 10 and kappa 11 and three for the omega repeat region: omega 8; omega 9 and omega 22. A polymorphism was observed inside t he repeat units of kappa and omega regions. There were six possible kappa r epeat units and seven possible omega repeat units. The presence of a partic ular pattern, containing kappa 14 and omega 16 repeat units, was associated with a lack of chloroquine susceptibility in 44 out of 46 cases. However, not all resistant isolates had this 'resistant' genotype. Among 43 resistan t isolates, 36 (84%) had the kappa 14 repeats sequence and 36 had the omega 16 repeats sequence. These results lend further support to linkage between cg2 polymorphisms and chloroquine resistance without excluding the existen ce of other resistance component(s). (C) 1999 Elsevier Science B.V. All rig hts reserved.