kb loci possible in the genome if all the genetic liability variance were attributable to loci like this, as this provides an upper limit to the contribution of such loci. The maximum number of loci can be high (maximum 543, with 543 100 kb blocks representing <2% of the genome) when there is only a single causal variant of GRR = 2 within a 100 kb region; we showed in the previous section that very common genotyped SNPs are unlikely to ever be the most associated SNP from a GWAS tagging single rare causal variants. When there are 9 causal variants, the maximum number of 100 kb regions required to explain all the variance for the models considered by Dickson et al. is only 59 (<0.2% of the genome), occurring when the GRR of each causal variant is 2 so that each block explains 1.4% of the variance. Dickson et al. showed that if 9 causal variants were segregating in a 10 Mb block that the most associated SNP may be positioned several Mb from the most distal causal variant it is coupled with. Even if associations from causal variants spanned several Mb for synthetic associations, to have an important
