Two Novel Mutations in the Gonadotropin-Releasing Hormone Receptor Gene in Brazilian Patients with Hypogonadotropic Hypogonadism and Normal Olfaction

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Abstract
Several point mutations in the GnRH receptor gene have been described in an autosomal recessive form of congenital isolated hy- pogonadotropic hypogonadism (HH). We investigated 17 Brazilian patients (10 males and 7 females) from 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 associated with low or normal levels of LH in both sexes and low levels of testosterone in males and of estradiol in females. All patients presented with a nor- mal sense of smell in an olfactory specific test. The coding region of the GnRH receptor gene was amplified by PCR and directly sequenced. A novel missense mutation, Arg139His, lo- cated in the conserved DRS motif at the junction of the third trans- membrane and the second intracellular loop of the GnRH receptor was identified in the homozygous state in one female with complete HH. The Arg139His mutation completely eliminated detectable GnRH-binding activity and prevented GnRH-induced stimulation of inositol phosphate accumulation in vitro. In another family, a new compound heterozygous mutation (Asn10Lys and Gln106Arg) was identified in four siblings (two males and two females) with partial HH. The Gln106Arg mutation, located in the first extracellular loop, has been previously described, and in vitro analysis indicated that the mutant receptor was able to bind GnRH, but with a reduced affinity. The Asn10Lys mutation in the extracellular amino-terminal domain of the receptor also reduced the affinity for GnRH in vitro. In this family we also identified a previ- ously 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 unrelated patients with sporadic HH without GnRH receptor loss of function mutations. No mutations were identified in the re- maining cases. A good correlation between genotype and phenotype was found in our patients. The woman, who is homozygous for the completely inactivating Arg139His mutation, has complete HH with undetectable serum basal LH and FSH levels that failed to respond to GnRH stimulation. In addition, the affected patients who are compound heterozygotes for the Asn10Lys/Gln106Arg mutations, have partial HH with low serum basal LH levels that were responsive to GnRH stimulation. No clinical or hormonal differences were found between HH pa- tients with and without mutations in the GnRH receptor gene, indi- cating that these data do not contribute to the identification of HH patients with GnRH receptor mutations. In conclusion, we report the first naturally occurring mutation within the conserved DRS motif of the GnRH receptor in a female with complete HH and a novel com- pound heterozygous mutation (Asn10Lys and Gln106Arg) in a family with partial HH, increasing the repertoire of the inactivating muta- tions of the GnRH receptor. (J Clin Endocrinol Metab 86: 2680 -2686, 2001)

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