The genetically isolated populations of Finland and Sardinia may not be a panacea for linkage disequilibrium mapping of common disease genes

The choice of which population to study in the mapping of common disease ge nes may be critical(1,2). Isolated founder populations, such as that found in Finland, have already proved extremely useful for mapping the genes for specific rare monogenic disorders(3,4) and are being used in attempts to ma p the genes underlying common, complex diseases(5-8). But simulation result s suggest that, under the common disease-common variant hypothesis(9-13), m ost isolated populations will prove no more useful for linkage disequilibri um (LD) mapping of common disease genes than large outbred populations(12). There is very little empirical data to either support or refute this concl usion at present(14-16) Therefore, we evaluated LD between 21 common micros atellite polymorphisms on chromosome 18q21 in 2 genetic isolates (Finland a nd Sardinia) and compared the results with those observed in two mixed popu lations (United Kingdom and United States of America). Mean levels of LD we re similar across all four populations. Our results provide empirical suppo rt for the expectation that genetic isolates like Finland and Sardinia will not prove significantly more valuable than general populations for LD mapp ing of common variants underlying complex disease.