Linkage disequilibrium (LD) and haplotype frequencies for LD blocks around significant SNPs on ECA 18. (a) Linkage disequilibrium (LD) around significant SNPs on ECA 18. Haplotype block 1 (62.01 – 62.15 Mb) contains the two most significant SNPs from the genome-wide association study (BIEC2-416680 and BIEC2-416681). There is only one known gene within this haplotype block, ZNF804A. Haplotype block 2 (62.15 – 62.76 Mb) contains the candidate gene FSIP2, while haplotype block 3 (62.76 – 65.87 Mb) contains the candidate genes ITGAV, CALCRL, COL3A1 and COL5A2. SNP BIEC2-417495 in haplotype block 4 (67.18 – 67.20 Mb) is in linkage disequilibrium (r2 = 0.8) with the myostatin (MSTN) gene, believed to be associated with racing performance [24–26], but there is only moderate LD (r2 < 0.3) between this SNP and the SNPs in haplotype block 1 which are significantly associated with catastrophic fracture risk (b) Observed haplotypes and their frequencies for the four haplotype blocks observed in the ECA 18 fracture associated region.