Patients with congenital hypogonadotropic hypogonadism are usually infertile, and most cases, therefore, occur sporadically, presumably as a result of de novo mutation. Because of the therapeutic use of pulsatile GnRH or gonadotropins, however, these patients may become fertile, and vertical disease transmission may increase. Segregation analysis has demonstrated X-linked, autosomal recessive and autosomal dominant inheritance patterns, suggesting the existence of several genes regulating GnRH secretion (61-63). Genes currently recognized to be involved in congenital hypogonadotropic hypogonadism include KAL (64), the GnRH receptor (13-15,65,66), DAX1 (67,68), and PROP 1 (69). Furthermore, sporadic cases of mutations in ANK 1 gene (70), SF-1 gene, LHX 3 gene (71), HESX1 gene (72) and leptin (Ob) gene (73), leptin receptor (Ob R) gene (74), and prohormone convertase 1 (PC 1) gene (75) have been reported. However, a genetic basis for IHH has been established in less than 20% of cases, leaving several autosomal and X-linked genes to await description (42) (see Chapter 5).
In clinical studies, there was evidence of familial transmission in approx 25% of cases, whereas the majority of cases (approx 75%) were sporadic (42,76). In familial and sporadic cases the X-linked mode of inheritance, characterized clinically by the predominance of males affected, the presence of unaffected female carriers and absent male-to-male transmission, accounted for the minority of patients (42,77). A few patients with IHH who received treatment for induction of ovulation or spermatogenesis and transmitted the condition to their offspring have been reported (76,78).
Given that the genetic basis of the majority of IHH patients remains unknown, it is difficult to provide accurate pretreatment counselling on the risk of the condition being inherited by the offspring. Nevertheless, the existence of a defined risk should be specifically discussed with all patients before fertility treatment (76).
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