Hypogonadotropic Hypogonadism 21 with or Without Anosmia, also known as hh21, is related to hypogonadotropic hypogonadism 2 with or without anosmia. An important gene associated with Hypogonadotropic Hypogonadism 21 with or Without Anosmia is FLRT3 (Fibronectin Leucine Rich Transmembrane Protein 3). Affiliated tissues include pituitary and bone, and related phenotypes are osteopenia and hearing impairment