Case-only analyses were conducted to describe the frequency of exposures overall and in relation to patient phenotype. Statistical analysis was performed using Sigma Stat Version 3.1 (Systat Software, Inc., Chicago, IL, USA), including 2 and Fisher's exact tests to determine differences in the proportion of patients with different environmental exposures. Odds ratios (ORs) and 95% CIs were calculated using GraphPad InStat version 3.06 (GraphPad Software, San Diego, CA, USA). P-values were adjusted for multiple testing using Holm's procedure [25] , using SAS System for Windows, version 9.1.3 and SAS Enterprise Guide Version 4.1 (SAS Institute, Cary, NC, USA).