Olfactory function in patients with hypogonadotropic hypogonadism: an all-or-none phenomenon?

Hypogonadotropic hypogonadism (HH) refers to a heterogeneous group of disorders of the hypothalamic-pituitary-gonadal axis typically associated with deficient release of gonadotropin-releasing hormone (GnRH) from the hypothalamus, consequent failure of the pituitary to secrete gonadotropins sufficient for full gonadal development, and subsequent failure of the patient to undergo puberty and achieve reproductive capacity. One of the best known forms of HH is Kallmann’s syndrome (KS), which is characterized by aplasia or hypoplasia of the olfactory bulbs and consequent anosmia or severely impaired olfactory function. It apparently results from a disruption in the migration of neurons from the olfactory placode to the bulb and hypothalamus early in development, and so provides a unique opportunity to investigate olfactory function in human subjects with congenitally incomplete peripheral systems. KS and idiopathic hypogonadotropic hypogonadism without anosmia (IHH) are both highly variable in phenotypic expression and may be associated with a variety of neurological, urinary, skeletal, and other anomalies.