Genome-wide linkage studies (GWLSs) have identified various genetic loci with potential involvement in TSD etiology, including the two genes Slit and Trk-like 1 (SLITRK1) and histidine decarboxylase (HDC) [12,13], but reproducibility has been unstable [12,13,14,15]. This evidence concerns the gene HDC and Tay-Sachs disease.