Meta-analysis is becoming an increasingly important tool in genome-wide association studies (GWAS) of complex genetic diseases and traits (de Bakker et al., 2008). Meta-analysis provides an efficient and practical strategy for detecting variants with modest effect sizes (Skol et al., 2007). We, and others, have used METAL for performing meta-analysis of GWAS to identify loci reproducibly associated with a variety of traits, such as type 2 diabetes (Scott et al., 2007; Zeggini et al., 2008), lipid levels (Kathiresan et al., 2008, 2009; Willer et al., 2008), BMI (Willer et al., 2009), blood pressure (Newton-Cheh et al., 2009) and fasting glucose levels (Prokopenko et al., 2009).
