Historic exposure to plague and present-day frequency of CCR5del32 in two isolated island communities of Dalmatia, Croatia.

AIM To assess the frequency of deletion of 32 base pairs in a CCR5 gene, shown to confer resistance to HIV infection, in two isolated island communities of Dalmatia, Croatia, with different histories of exposure to (plague) during the medieval period and beyond. METHODS Random samples of 100 individuals from highly isolated communities of Lopar (island of Rab) and Komiza (island of Vis) were selected in 2002 and their DNA was extracted. An extremely high level of 3-generational endogamy was found in both communities (98% and 91%, respectively), indicating very limited gene flow, which was confirmed by available historic records. The two settlements also differed in their historic exposure to plague: between 1449 and 1456, Lopar was decimated by plague, while Komiza remained unaffected. Genotyping of the CCR5 polymorphism was performed using the polymerase chain reaction (PCR) method with primers flanking the region containing 32-bp deletion. RESULTS The frequency of CCR5del32 in Lopar was 6.0% and in Komiza 1.5% (P=0.037). A previous study in 303 random Croatian blood donors showed a frequency of CCR5 32bp deletion of 7.1%. CONCLUSION This study does not rule out the possible role of plague in positive selection at CCR5del32. However, analyses of further neighboring isolated island communities need to be made in order to provide more substantial support for this hypothesis.