Until recently, the field of complex disease genetics had been plagued by irreproducibility of published results [1,2]. In retrospect, studies with small sample sizes given what are now known to be small effects [3], limited coverage of the genetic variability [4] and liberal use of statistical significance thresholds for claiming discovery were probably responsible for this poor replication record. The last few years have witnessed changes leading to the feasibility of genome-wide association (GWA) scans and better study designs. Larger samples have become available and researchers have recognised the value of collaborating to combine resources [5]. Advances in genotyping technologies have enabled high-throughput pipelines and accurate, reproducible genotyping. Finally, efforts like the International HapMap project [4], have improved our understanding of human sequence variation both by providing a more complete catalogue of common SNPs and by helping to characterise linkage disequilibrium (LD) patterns across the genome. Several large-scale GWA scans for common complex diseases have been carried out in the last couple of years, taking advantage of these advances [6].
