BMP4 and sirenomelia: Indeed, loss of a single copy of Bmp4 and both copies of Bmp7 in Bmp4flox/+Bmp7flox/flox compound mutant mice (Hoxa3-Cre;Bmp4flox/+Bmp7flox/flox) resulted in hindlimb fusion (Fig. 6 D) as well as loss of the bladder and anal stenosis, essential diagnotic features of sirenomelia (n = 3) (Fig. 6 H).