Tourette syndrome SNP-based heritability was estimated on the liability scale, assuming a population prevalence of 0.8% (21), using both LDSC (18) and, in GWAS1 and GWAS2 samples after excluding Ashkenazi Jewish samples, using genotype-level data in a linear mixed model framework (7). To compare the relative polygenic burden of Tourette syndrome samples collected with different ascertainment methods, the Tourette GWAS1 and GWAS2 datasets were separated into 3 groups: 1) GWAS1 cases (25% from affected sib-pair families)(10); 2) GWAS2 cases recruited through Tourette syndrome specialty clinics; 3) GWAS2 cases recruited via email from the membership of the Tourette Association of America and assessed with a web-based phenotyping instrument (12). Following additional stringent quality control of SNPs and samples (Supplemental Methods), the SNP-based heritability of each ascertainment group was estimated both separately and jointly.
