HOXA11 and pregnancy: The occurrence of tubal pregnancy in the setting of an estrogen-unresponsive endometrium in 2 of the 3 sisters suggests the existence of an abnormal uterine environment unfavorable for implantation of the embryo, which may be similar in some manner to the disrupted FRT functional patterning observed in Hoxa10–/– and Hoxa11–/– mice (33, 34), as well as in Wnt7a–/– mice (30).