Kallmann syndrome is a genetic condition where the primary symptom is a failure to start puberty or a failure to fully complete it. It occurs in both males and females and has the additional symptoms of hypogonadism and almost invariably infertility. Kallmann syndrome also features the additional symptom of an altered sense of smell; either completely absent (anosmia) or highly reduced (hyposmia). Kallmann syndrome occurs when the hypothalamic neurons that are responsible for releasing gonadotropin-releasing hormone (GnRH neurons) fail to migrate into the hypothalamus during embryonic development.