Importantly, each of these cytogenetic findings have clarified the genetics of HSCR: DS-associated HSCR is now known to be partially mediated through the RET low-penetrance enhancer polymorphism [10], [11]; the deletions at 10q, 13q and 2q contributed to the positional identification of RET[12], EDNRB[13] and ZFHX1B[14], respectively; and, the 17q locus harbors a novel dosage-sensitive HSCR gene [8], [9]. Here, RET is linked to Dravet syndrome.