SLC6A4 and Tourette syndrome: SERT is encoded by SLC6A4, which has been implicated in GTS aetiology by several studies: higher blood SLC6A4 mRNA expression levels were found to correlate with tic severity in GTS [35], elevated SLC6A4 expression was found in the striatum of rat models of GTS [36] and the rare SLC6A4 gain-of-function (GOF) variant Ile425Val known to modulate SERT activity was reported to have a higher prevalence in GTS individuals compared to controls [17,37].