There were 410 SNPs genotyped within the eight LD blocks containing the celiac associated regions shown in Table 1. These 410 SNPs were tested for association with the celiac-related conditions dermatitis herpetiformis (DH) and microscopic colitis (MC). Of the 1550 celiac disease cases in the study, 59 (3.8%) and 69 (4.5%) were positive for DH and MC, respectively. For DH, most studies suggest that the prevalence of DH in celiac disease is between 5 and 10%.[2] For MC, the prevalence in this study is consistent with previous reports of 4.3% of celiac patients having concomitant MC.[16] Microscopic colitis includes lymphocytic colitis (LC) and collagenous colitis (CC). The association between MC and celiac disease is well recognized, as both are associated with HLA-DQ2.[17], [18] For the case-control analysis, the genotype distributions of the 59 and 69 respective cases were compared against all celiac cases without these conditions and the controls, while adjusting for celiac disease status. The inclusion of the non-phenotyped dbGaP controls was not expected to have a detrimental effect on the statistical power given the rarity of the conditions.
