Researchers at the London School of Hygiene & Tropical Medicine found Plasmodium falciparum malaria parasites with a mutation to the gene Ap2mu were less sensitive to the antimalarial drug artemisinin. A study in 2013, also led by the School, suggested an initial link between a mutation in the ap2mu gene and low levels of malaria parasites remaining in the blood of Kenyan children after they had been treated. However, further research was needed to confirm if these genetic characteristics represented an early step towards resistance. In the new study, researchers genetically altered the malaria parasite in the laboratory to mutate ap2mu in the same way that had been observed in Kenya. They found the altered parasite was significantly less susceptible, requiring 32% more drug to be killed by artemisinin. The genetically altered parasite was also 42.4% less susceptible to the traditional antimalarial drug, quinine. "We now know that the gene ap2mu is an important factor in determining how well our drugs kill malaria parasites. We will be conducting laboratory and field studies to more accurately measure the impact of mutations in the ap2mu gene. We hope our findings will help understand resistance of malaria to drugs, and potentially be an important tool for monitoring malaria treatment in the future." The World Health Organization estimates more than half a million people die from malaria every year, mostly children under five. Plasmodium falciparum is the most deadly form of the malaria parasite.