Gonadotropin-releasing hormone insensitivity

Gonadotropin-releasing hormone (GnRH) insensitivity also known as Isolated gonadotropin-releasing hormone (GnRH) deficiency (IGD) is a rare autosomal recessive genetic and endocrine syndrome which is characterized by inactivating mutations of the gonadotropin-releasing hormone receptor (GnRHR) and thus an insensitivity of the receptor to gonadotropin-releasing hormone (GnRH), resulting in a partial or complete loss of the ability of the gonads to synthesize the sex hormones. The condition manifests itself as isolated hypogonadotropic hypogonadism (IHH), presenting with symptoms such as delayed, reduced, or absent puberty, low or complete lack of libido, and infertility, and is the predominant cause of IHH when it does not present alongside anosmia.

Signs and symptoms

There is a relatively broad spectrum of clinical signs and symptoms that can occur in, ranging from complete absence of sexual development to partial completion of puberty that does not subsequently progress. Of note, the X-linked form of Kallmann syndrome (KS) form of GnRH insensitivity relating to mutations in the ANOS1 gene has the most consistent severe phenotypic presentation (i.e., prepubertal testes size and complete absence of gonadotropin-releasing hormone [GnRH]-induced luteinizing hormone [LH] pulsations during frequency sampling studies) of all of the genes associated with this condition.

GnRH insensitivity can present at any age, but the presenting signs and symptoms are a function of the age-related period of reproductive activity.

During the neonatal period, boys with the more severe cases of GnRH insensitivity can present with microphallus and/or cryptorchidism, presumably due to in utero and/or neonatal GnRH deficiency; approximately one-half of boys with microphallus have GnRH insensitivity as the underlying diagnosis. In comparison, newborn girls with GnRH insensitivity have no obvious abnormal reproductive tract findings that might provide clues to the diagnosis. However, in both sexes, other congenital nonreproductive features may be present (e.g., midline facial defects, skeletal abnormalities).

During childhood, since the hypothalamic GnRH-pituitary-gonadal axis is quiescent, a diagnosis of GnRH insensitivity can generally be heralded only in the presence of nonreproductive phenotypes (e.g., the lack of sense of smell in some patients [anosmia] or skeletal abnormalities, such as cleft lip/cleft palate, hearing deficits, or syndactyly).

At puberty, patients of both sexes can present with a complete form of GnRH insensitivity that is characterized by a failure to initiate sexual maturation (e.g., lack of secondary sexual characteristics, primary amenorrhea in girls, lack of virilization in boys) and failure to establish a pubertal growth spurt.