Recently, Abelson and colleagues identified a patient affected with GTS and ADHD with a de novo chromosome 13 inversion, inv(13)(q31.1;q33.1) [85, 86]. Out of three genes that mapped within 500 kilobases of the chromosomal breakpoints, the Slit and Trk-like family member 1 (SLITRK1) was selected for further study based on its homology to the axon guidance molecule SLIT. SLITRK1 was screened in 174 GTS affected individuals, and three subjects were found to carry functional variations in this gene: One frameshift mutation and two unrelated occurrences of a sequence variation in the 3′ untranslated region of the gene (var321) that disrupted the binding site for a microRNA miR-189. These variants were absent from 3,600 and 4,296 control chromosomes respectively [85]. While another study [87] detected two independent, novel, non-synonymous sequence changes in SLITRK1 in a set of 44 families with trichotillomania, an OCD-spectrum disorder that has been previously hypothesized to be genetically related to GTS, additional studies in GTS and OCD samples have failed to replicate association with these variants (Table 2) [86, 88–93]. The largest study to date screened over
