BMP4 and Anophthalmia: The recent report that anophthalmia occurs in embryos from crosses between Bmp4 heterozygous mutants and mice homozygous for a disrupted allele of Twisted gastrulation (Tsg), a BMP binding protein that is thought to enhance BMP4 signaling in the eye [87], also indicates that excess BMP4 signaling may be as harmful as loss of function.