A Major Susceptibility Locus on Chromosome 22q12 Plays a Critical Role in the Control of Kala-Azar

Kala-azar (KA) is a life-threatening protozoal disease caused by Leishmania parasites (L. donovani, L. chagasi, and L. infantum). The disease, which is also called “visceral leishmaniasis,” is prevalent in Africa, South America, Asia, and the Mediterranean basin. Epidemics occur periodically, killing a large number of infected individuals. Factors determining whether a patient remains asymptomatic or develops KA are still largely unknown. In a previous study that was performed during an outbreak of KA in a village on the Ethiopian-Sudanese border, we showed that KA was more frequent in certain families and ethnic groups, thereby suggesting that host genetic factors play an important role in the development of the disease. Here, we report the results of a genomewide linkage study performed on 63 Sudanese families selected from the most affected ethnic group and including 169 children with KA. Significant linkage (LOD score 3.50 [P=3×10(-5)] in all patients; LOD score 3.90 [P=10(-5)] in patients who were affected early in the outbreak) was obtained with markers on chromosome 22q12. These results are the first evidence of a major genetic effect on the development of human KA. They may lead to identification of genes critical in the pathogenesis of this disease and to new therapeutic interventions against this parasite, which is developing resistance to available drugs

Insight into the wild origin, migration and domestication history of the fine flavour Nacional Theobroma cacao L. variety from Ecuador.

Ecuador's economic history has been closely linked to Theobroma cacao L cultivation, and specifically to the native fine flavour Nacional cocoa variety. The original Nacional cocoa trees are presently in danger of extinction due to foreign germplasm introductions. In a previous work, a few non-introgressed Nacional types were identified as potential founders of the modern Ecuadorian cocoa population, but so far their origin could not be formally identified. In order to determine the putative centre of origin of Nacional and trace its domestication history, we used 80 simple sequence repeat (SSR) markers to analyse the relationships between these potential Nacional founders and 169 wild and cultivated cocoa accessions from South and Central America. The highest genetic similarity was observed between the Nacional pool and some wild genotypes from the southern Amazonian region of Ecuador, sampled along the Yacuambi, Nangaritza and Zamora rivers in Zamora Chinchipe province. This result was confirmed by a parentage analysis. Based on our results and on data about pre-Columbian civilization and Spanish colonization history of Ecuador, we determined, for the first time, the possible centre of origin and migration events of the Nacional variety from the Amazonian area until its arrival in the coastal provinces. As large unexplored forest areas still exist in the southern part of the Ecuadorian Amazonian region, our findings could provide clues as to where precious new genetic resources could be collected, and subsequently used to improve the flavour and disease resistance of modern Ecuadorian cocoa varieties