Several alleles of the multidrug-resistance gene are closely linked to chloroquine resistance in Plasmodium falciparum

Chloroquine is the drug most frequently used to treat malaria, but in many areas of the world, the parasite Plasmodium falciparum, which causes malaria, has become resistant to chloroquine. It has been shown that chloroquine-resistant parasites can rid themselves of chloroquine, using a protein which functions as a transporter molecule. A similar protein has been identified in the resistance of cancer cells to many different types of drugs; this protein is encoded by the gene mdr. A homologue to mdr has been found in Plasmodium falciparum, and there are multiple copies of the gene in chloroquine-resistant isolates. The genes from different isolates have been sequenced, and mutations, or changes, have been found compared with genes from isolates that are sensitive to chloroquine. However, resistance to chloroquine does not occur as frequently as it would if the resistance was simply due to the inheritance of the one mutated gene. The inheritance of the mutated mdr gene is necessary, but not sufficient, for drug resistance. Therefore, it is thought that more than one gene is needed for the resistance of Plasmodium falciparum to chloroquine to occur. Further study is need to identify the other genes and how they interact with the transporter protein gene. (Consumer Summary produced by Reliance Medical Information, Inc.)