Molecular Genetic Analysis of Normosmic Hypogonadotropic Hypogonadism in a Turkish Population: Identification and Detailed Functional Characterization of a Novel Mutation in the Gonadotropin-Releasing Hormone Receptor Gene

Abstract

Background/Aims: Currently known mutations account for less than 15% of cases with normosmic hypogonadotropic hypogonadism (nIHH). The objective of the study was to identify novel hereditary associations in the pathogenesis of nIHH. Methods: We investigated 26 Turkish patients with nIHH (21 males and 5 females) from 22 families. The coding regions of the GnRH receptor, GnRH1, GPR54, and KISS1 genes were directly sequenced. Results: In two sisters, a novel homozygous missense mutation, R139C, located in the conserved DRS motif at the junction of the third transmembrane and the second intracellular loop of the GnRH receptor was identified. The R139C mutation almost completely abolished plasma membrane expression while having little effect on GnRH-binding affinity. The mutant receptor expression was rescued by a membrane-permeant, non-peptide GnRH receptor antagonist IN3. Conclusions: Consistent with the previous studies we were able to find mutations in only 7.6% of a well-defined group of patients with nIHH, which further suggests that yet unidentified genetic associations to explain nIHH exist.

G Protein-Coupled Receptor Trafficking in Health and Disease: Lessons Learned to Prepare for Therapeutic Mutant Rescue in Vivo

“…In both receptors, mutations in the highly conserved motifs E/DRY (located at the boundary of the TM helix 3 and the second intracellular loop and permutated to DRS in the GnRHR and to DRH in the V2R) and D/NPxxY (in the seventh TM helix) have been reported. These motifs have important structural and functional roles in many GPCRs (Gether and Kobilka, 1998;Rovati et al, 2007); GnRHRs and V2Rs bearing mutations in this motif are misfolded receptors that may be partially or completely rescuable by pharmacoperones (Leañ os- Bernier et al, 2004cBernier et al, ,2006Topaloglu et al, 2006). It has been shown recently that in some GPCRs (including the V2R), mutations in the E/DRY motif promote constitutive receptor endocytosis as a result of increased receptor phosphorylation and arrestin association (Shi et al, 1998;Barak et al, 2001;Wilbanks et al, 2002).…”

“…Of the 21 mutations of the GnRHR reported in patients with HH, 7 mutant receptors were partially functional when expressed in heterologous cell systems, and the remaining mutant receptors were nonfunctional Leañ os-Miranda et al, 2002;Topaloglu et al, 2006). When several of the nonfunctional receptors were coexpressed with the wild-type receptor in heterologous cell systems, it was discovered that these nonfunctional receptors also inhibit wild-type GnRH receptor function, a DN effect (Fig.…”

“…This has added to the facility of use of these mutants for research models. In the case of the GnRHR, all but three [Ser 168 Arg, Ser 217 Arg, and the truncated L 314 X (stop)] of the 17 mutants tested were completely or partially rescued 234 with pharmacoperones Leañ osMiranda et al, 2002;Janovick et al, 2003a;Topaloglu et al, 2006). It has been possible to show that the Ser 168 Arg and Ser 217 Arg GnRHRs are mutants in which the thermodynamic changes leading to receptor distortion are too great to effect rescue (Janovick et al, 2006).…”

Non-syndromic congenital hypogonadotropic hypogonadism: clinical presentation and genotype–phenotype relationships

“…However, conflicts between the results of receptor function studies in vitro and the clinical phenotype have also been described in unrelated subjects or even within a given family having the same mutation and different degrees of gonadotropin deficiency (73,90). The most consistent characteristic of patients with GNRHR mutations is their pituitary resistance to pulsatile GNRH administration when the phenotype is severe and their spontaneous LH secretion is non-pulsatile (73,90). This hormonal profile distinguishes these patients from those with mutations of GPR54/KISS1R, TAC3, or TACR3, whose pituitary, even in severe forms, seems to be highly sensitive to pulsatile exogenous GNRH, as will be discussed below.…”

Estudo do gene do receptor de GnRH (GNRHR) no hipogonadismo hipogonadotrófico isolado normósmico e atraso constitucional do crescimento e desenvolvimento

“…Embora nas leis da evolução as mutações prejudiciais sejam progressivamente eliminadas do pool genético humano, as mutações conhecidas como fundadoras persistem e são transmitidas aos descendentes (54) . (58,59) .  Uma boa correlação genótipo-fenótipo foi observada nos pacientes com HHI normósmico portadores de mutações no GNRHR.…”