TAC3 and hypogonadotropic hypogonadism: Such dissociation between LH and FSH levels has previously been demonstrated in individuals with hypogonadotropic hypogonadism secondary to mutations in TAC3 or TACR3 that encode NKB and NK3R, respectively.(28) Furthermore, while we demonstrated that circulating estradiol levels were unaltered, we are unable to exclude inhibition of local estradiol synthesis at the neuronal level.