SNP imputation was conducted on all genotype data for the primary meta-analyses using the 1000 Genomes Project Phase 1 integrated haplotypes (December 2013 release, with singleton sites removed) as the reference panel (15). ShapeIT was used to phase genotype data, followed by imputation with IMPUTE v2. SNPs with Information score <0.6 or Certainty <0.9 were excluded.
