Goat XX fetuses lacking Foxl2 have gonads resembling testes and the induced absence of Foxl2 in adult XX mice results in trans-differentiation of the ovaries into a testis-like gonad.9, 10, 11 In humans, heterozygous loss-of-function FOXL2 mutations are associated with autosomal-dominant blepharophimosis-ptosis-epicanthus inversus syndrome (BPES [MIM: 110100]) either with (type I) or without (type 2) ovarian insufficiency as well as ovarian insufficiency without BPES (MIM: 608996), but homozygous FOXL2 disruption has not been described.10 This evidence concerns the gene FOXL2 and ovarian dysfunction.