Congenital abnormalities leading to hypogonadotropic hypogonadism are rare but are well described (Table 1). Congenital hypogonadotropic hypogonadism (CHH) is usually the consequence of deficient GnRH secretion or function. CHH can occur by itself (normosmic CHH) or can be associated with anosmia and other midline defects and is termed Kallmann syndrome. Mutations in both LH-P and FSH-P subunits have been reported to cause CHH. Recently, leptin and leptin-R gene mutations have also been demonstrated to cause hypogonadotropic hypogonadism. CHH may also be associated with impaired production of other pituitary hormones, often resulting from reduced or absent expression of transcription factors such as PROP-1 or HEXS-1. Finally, hypogonadotropic hypogonadism can be a component of complex syndromes with multiple somatic abnormalities, such as morbid obesity (Prader-Willi), cerebellar ataxia (26), cranial nerves palsies and peripheral neuropathy (27), congenital spherocy-tosis (28). CHH is differentiated from primary testicular disease by the demonstration of low/normal gonadotropin levels in the setting of low T levels and impaired sper-matogenesis. The diagnosis also requires normal radiological imaging of the hypothal-amic and pituitary region.
Differential Diagnosis of Congenital Hypogonadotropic Hypogonadism
Congenital Idiopathic hypogonadotropic hypogonadism (CIHH) Anosmic (Kallmann syndrome) Nonansomic: normosmic IHH (nIHH) Fertile eunuch syndrome Adrenal hypoplasia congenita Genetic defects of the gonadotropin subunits FSH-ß mutations LH-ß mutations Genetic defects of leptin and leptin receptor genes
Hypogonadotropic hypogonadism associated with other pituitary hormone deficiencies Prop-1 mutations HERS1 mutations Complex syndrome, including hypogonadotropic hypogonadism Prader-Willi syndrome
Hypogonadotropic hypogonadism and congenital spherocytosis Hypogonadotropic hypogonadism and Moebius syndrome Hypogonadotropic hypogonadism and cerebral ataxia Hypogonadotropic hypogonadism and retinitis pigmentosa
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