SLITRK1 and Timothy syndrome: However, despite the earlier excitement and optimism about gene discovery for TS through GWLS approach, and some chromosomal regions have been implicated in some TS families, no gene or causal mutation of major effect has been discovered for the above-mentioned TS loci, except for the SLITRK1 locus on chromosome 13 [51] and the HDC locus on chromosome 15 [52].