HOXD13 and Syndactyly type 2: This phenomenon is more comparable to the one observed in synpolydactyly, in which the poly-A at the 3′end of HOXD13 might have originated by unequal crossing over as it is quite stable when transmitted across generations (Warren, 1997), as opposed to dynamic mutations observed in neurological conditions, which have arisen only once (Virtaneva et al., 1997; Gatchel and Zoghbi, 2005; Mirkin, 2007; La Spada and Taylor, 2010; McMurray, 2010; DeJesus-Hernandez et al., 2011; Renton et al., 2011; Usdin et al., 2015; Haeusler et al., 2016).