SLC6A4 and Compulsive behaviors: However, in patients with TS (with and without OCD, n = 18), tic severity (according to YGTSS-TTS) was negatively correlated with SERT binding in pons (Logan fixed: r-sq = 0.2320, p = 0.0429, Logan fitted: r-sq = 0.2623, p = 0.0298) – but no other brain area - suggesting that SERT binding is higher in less severely affected patients.