Acta Tropica 95 (2005) 226–232 Genetic diversity of the msp-1 locus and symptomatic malaria in south-west Nigeria O.K. Amodu a,∗ , A.A. Adeyemo a,b,c , O.O. Ayoola a,c , R.A. Gbadegesin a , A.E. Orimadegun c , A.K. Akinsola c , P.E. Olumese d , O.O. Omotade a,c a College of Medicine, Institute of Child Health, University of Ibadan, Ibadan, Nigeria b National Human Genome Center, Howard University, Washington, DC, USA c Department of Paediatrics, University College Hospital, Ibadan, Nigeria d RBM, World Health Organization, Geneva, Switzerland Received 29 April 2005; received in revised form 31 May 2005; accepted 6 June 2005 Available online 15 July 2005 Abstract Genetic characteristics of Plasmodium falciparum may play a role in the clinical severity of malaria infection. We have studied the association between diversity at the merozoite surface protein-1 (msp-1) locus and the severity of disease in childhood malaria in Ibadan, south-west Nigeria. Two hundred and twenty-three children (median age of 34.5 months) presenting with malaria were enrolled into the study. They comprised 53 children with asymptomatic malaria (ASM), 101 with acute uncomplicated malaria (UM) and 69 with severe malaria (SM). Genotyping of the msp-1 locus was by polymerase chain reaction. The distribution of msp-1 alleles was significantly different between the three groups. Asymptomatic malaria samples had a higher median number of alleles than the other two groups. The type of msp-1 allele detected was significantly associated with the clinical category of malaria. The absence of K1 alleles was associated with a three-fold increase risk of UM and a four-fold increased risk of SM when compared with asymptomatic malaria. The absence of MAD20 alleles was associated with a five-fold increase risk of UM and an eight-fold increase of SM. We have found an association between the msp-1 locus of P. falciparum and clinical severity of malaria in a sample of Nigerian children. Our findings show that the presence of the K1 and MAD20 alleles was significantly associated with ASM and consequently a reduced risk of developing the symptomatic disease. © 2005 Elsevier B.V. All rights reserved. Keywords: Malaria; Plasmodium falciparum; Severity; msp-1 ∗ Corresponding author. Tel.: +234 2 2411081; fax: +234 2 2411768. E-mail address: amkemi@hotmail.com (O.K. Amodu). 1. Introduction Falciparum malaria remains one of the major public health hazards in sub-Saharan Africa. Children under the age of five years are the most susceptible to the 0001-706X/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.actatropica.2005.06.017