Two novel mutations in the gonadotropin-releasing hormone receptor gene inBrazilian patients with hypogonadotropic hypogonadism and normal olfaction

Several point mutations in the GnRH receptor gene have been described in an autosomal recessive form of congenital isolated hypogonadotropic hypogonad ism (HH). We investigated 17 Brazilian patients (10 males and 7 females) fr om 14 different families, with HH and normal olfaction. The diagnosis of HH was based on absent or incomplete sexual development after 17 yr of age as sociated with low or normal levels of LH in both sexes and low levels of te stosterone in males and of estradiol in females. All patients presented wit h a normal sense of smell in an olfactory specific test. The coding region of the GnRH receptor gene was amplified by PCR and direct ly sequenced. A novel missense mutation, Arg(139)His, located in the conser ved DRS motif at the junction of the third transmembrane and the second int racellular loop of the GnRH receptor was identified in the homozygous state in one female with complete HH. The Arg(139)His mutation completely elimin ated detectable GnRH-binding activity and prevented GnRH-induced stimulatio n of inositol phosphate accumulation in vitro. In another family, a new compound heterozygous mutation (Asn(10)Lys and Gln (106)Arg) was identified in four siblings (two males and two females) with partial HH. The Gln(106)Arg mutation, located in the first extracellular lo op, has been previously described, and in vitro analysis indicated that the mutant receptor was able to bind GnRH, but with a reduced affinity. The As n(10)Lys mutation in the extracellular amino-terminal domain of the recepto r also reduced the affinity for GnRH in vitro. In this family we also ident ified a previously described silent polymorphism at amino acid residue 151 in the second intracellular loop that segregated with the two inactivating mutations of the GnRH receptor. This polymorphism was also found in two unr elated patients with sporadic HH without GnRH receptor loss of function mut ations. No mutations were identified in the remaining cases. A good correlation between genotype and phenotype was found in our patients . The woman, who is homozygous for the completely inactivating Arg(139)His mutation, has complete HH with undetectable serum basal LH and FSH levels t hat failed to respond to GnRH stimulation. In addition, the affected patien ts who are compound heterozygotes for the Asn(10)Lys/Gln(106)Arg mutations, have partial HH with low serum basal LH levels that were responsive to GnR H stimulation. No clinical or hormonal differences were found between KH patients with and without mutations in the GnRH receptor gene, indicating that these data do not contribute to the identification of KH patients with GnRH receptor mut ations. In conclusion, we report the first naturally occurring mutation wit hin the conserved DRS motif of the GnRH receptor in a female with complete HH and a novel compound heterozygous mutation (Asn(10)Lys and Gln(106)Arg) in a family with partial HH, increasing the repertoire of the inactivating mutations of the GnRH receptor.