Kisspeptin Restores Pulsatile LH Secretion in Patients with Neurokinin B Signaling Deficiencies:Physiological, Pathophysiological and Therapeutic Implications

Pulsatile gonadotropin-releasing hormone (GnRH) is crucial to normal reproductive function and abnormalities in pulse frequency give rise to reproductive dysfunction. Kisspeptin and neurokinin B (NKB), neuropeptides secreted by the same neuronal population in the ventral hypothalamus, have emerged recently as critical central regulators of GnRH and thus gonadotropin secretion. Patients with mutations resulting in loss of signaling by either of these neuroendocrine peptides fail to advance through puberty but the mechanisms mediating this remain unresolved. We report here that continuous kisspeptin infusion restores gonadotropin pulsatility in patients with loss-of-function mutations in NKB (TAC3) or its receptor (TAC3R), indicating that kisspeptin on its own is sufficient to stimulate pulsatile GnRH secretion. Moreover, our findings suggest that NKB action is proximal to kisspeptin in the reproductive neuroendocrine cascade regulating GnRH secretion, and may act as an autocrine modulator of kisspeptin secretion. The ability of continuous kisspeptin infusion to induce pulsatile gonadotropin secretion further indicates that GnRH neurons are able to set up pulsatile secretion in the absence of pulsatile exogenous kisspeptin.Publisher PDFPeer reviewe

R31C GNRH1 mutation and congenital hypogonadotropic hypogonadism

Normosmic congenital hypogonadotropic hypogonadism (nCHH) is a rare reproductive disease leading to lack of puberty and infertility. Loss-of-function mutations of GNRH1 gene are a very rare cause of autosomal recessive nCHH. R31C GNRH1 is the only missense mutation that affects the conserved GnRH decapeptide sequence. This mutation was identified in a CpG islet in nine nCHH subjects from four unrelated families, giving evidence for a putative “hot spot”. Interestingly, all the nCHH patients carry this mutation in heterozygosis that strikingly contrasts with the recessive inheritance associated with frame shift and non-sense mutations. Therefore, after exclusion of a second genetic event, a comprehensive functional characterization of the mutant R31C GnRH was undertaken. Using different cellular models, we clearly demonstrate a dramatic reduction of the mutant decapeptide capacity to bind GnRH-receptor, to activate MAPK pathway and to trigger inositol phosphate accumulation and intracellular calcium mobilization. In addition it is less able than wild type to induce lh-beta transcription and LH secretion in gonadotrope cells. Finally, the absence of a negative dominance in vitro offers a unique opportunity to discuss the complex in vivo patho-physiology of this form of nCHH

The genetic diagnosis of rare endocrine disorders of sex development and maturation : a survey among Endo-ERN centres

Differences of sex development and maturation (SDM) represent a heterogeneous puzzle of rare conditions with a large genetic component whose management and treatment could be improved by an accurate classification of underlying molecular conditions, and next-generation sequencing (NGS) should represent the most appropriate approach. Therefore, we conducted a survey dedicated to the use and potential outcomes of NGS for SDM disorders diagnosis among the 53 health care providers (HCP) of the European Reference Network for rare endocrine conditions. The response rate was 49% with a total of 26 HCPs from 13 countries. All HCPs, except 1, performed NGS investigations for SDM disorders on 6720 patients, 3764 (56%) with differences of sex development (DSD), including 811 unexplained primary ovarian insufficiency, and 2956 (44%) with congenital hypogonadotropic hypogonadism (CHH). The approaches varied from targeted analysis of custom gene panels (range: 11-490 genes) in 81.5% of cases or whole exome sequencing with the extraction of a virtual panel in the remaining cases. These analyses were performed for diagnostic purposes in 21 HCPs, supported by the National Health Systems in 16 cases. The likelihood of finding a variant ranged between 7 and 60%, mainly depending upon the number of analysed genes or criteria used for reporting, most HCPs also reporting variants of uncertain significance. These data illustrate the status of genetic diagnosis of DSD and CHH across Europe. In most countries, these analyses are performed for diagnostic purposes, yielding highly variable results, thus suggesting the need for harmonization and general improvements of NGS approaches.publishersversionPeer reviewe

Congenital Hypogonadotropic Hypogonadism Due to GNRH Receptor Mutations in Three Brothers Reveal Sites Affecting Conformation and Coupling

Congenital hypogonadotropic hypogonadism (CHH) is characterized by low gonadotropins and failure to progress normally through puberty. Mutations in the gene encoding the GnRH receptor (GNRHR1) result in CHH when present as compound heterozygous or homozygous inactivating mutations. This study identifies and characterizes the properties of two novel GNRHR1 mutations in a family in which three brothers display normosmic CHH while their sister was unaffected. Molecular analysis in the proband and the affected brothers revealed two novel non-synonymous missense GNRHR1 mutations, present in a compound heterozygous state, whereas their unaffected parents possessed only one inactivating mutation, demonstrating the autosomal recessive transmission in this kindred and excluding X-linked inheritance equivocally suggested by the initial pedigree analysis. The first mutation at c.845 C>G introduces an Arg substitution for the conserved Pro 282 in transmembrane domain (TMD) 6. The Pro282Arg mutant is unable to bind radiolabeled GnRH analogue. As this conserved residue is important in receptor conformation, it is likely that the mutation perturbs the binding pocket and affects trafficking to the cell surface. The second mutation at c.968 A>G introduces a Cys substitution for Tyr 323 in the functionally crucial N/DPxxY motif in TMD 7. The Tyr323Cys mutant has an increased GnRH binding affinity but reduced receptor expression at the plasma membrane and impaired G protein-coupling. Inositol phosphate accumulation assays demonstrated absent and impaired Gαq/11 signal transduction by Pro282Arg and Tyr323Cys mutants, respectively. Pretreatment with the membrane permeant GnRHR antagonist NBI-42902, which rescues cell surface expression of many GNRHR1 mutants, significantly increased the levels of radioligand binding and intracellular signaling of the Tyr323Cys mutant but not Pro282Arg. Immunocytochemistry confirmed that both mutants are present on the cell membrane albeit at low levels. Together these molecular deficiencies of the two novel GNRHR1 mutations lead to the CHH phenotype when present as a compound heterozygote

Isolated familial hypogonadotropic hypogonadism and a <em>GNRH1</em> mutation

We investigated whether mutations in the gene encoding gonadotropin-releasing hormone 1 (GNRH1) might be responsible for idiopathic hypogonadotropic hypogonadism (IHH) in humans. We identified a homozygous GNRH1 frameshift mutation, an insertion of an adenine at nucleotide position 18 (c.18-19insA), in the sequence encoding the N-terminal region of the signal peptide-containing protein precursor of gonadotropin-releasing hormone (prepro-GnRH) in a teenage brother and sister, who had normosmic IHH. Their unaffected parents and a sibling who was tested were heterozygous. This mutation results in an aberrant peptide lacking the conserved GnRH decapeptide sequence, as shown by the absence of immunoreactive GnRH when expressed in vitro. This isolated autosomal recessive GnRH deficiency, reversed by pulsatile GnRH administration, shows the pivotal role of GnRH in human reproduction

Compromised Volumetric Bone Density and Microarchitecture in Men With Congenital Hypogonadotropic Hypogonadism

Abstract Context Men with congenital hypogonadotropic hypogonadism (CHH) and Kallmann syndrome (KS) have both low circulating testosterone and estradiol levels. Whether bone structure is affected remains unknown. Objective To characterize bone geometry, volumetric density and microarchitecture in CHH/KS. Methods This cross-sectional study, conducted at a single French tertiary academic medical center, included 51 genotyped CHH/KS patients and 40 healthy volunteers. Among CHH/KS men, 98% had received testosterone and/or combined gonadotropins. High-resolution peripheral quantitative computed tomography (HR-pQCT), dual-energy x-ray absorptiometry (DXA), and measurement of serum bone markers were used to determine volumetric bone mineral density (vBMD) and cortical and trabecular microarchitecture. Results CHH and controls did not differ for age, body mass index, and levels of vitamin D and PTH. Despite long-term hormonal treatment (10.8 ± 6.8 years), DXA showed lower areal bone mineral density (aBMD) in CHH/KS at lumbar spine, total hip, femoral neck, and distal radius. Consistent with persistently higher serum bone markers, HR-pQCT revealed lower cortical and trabecular vBMD as well as cortical thickness at the tibia and the radius. CHH/KS men had altered trabecular microarchitecture with a predominant decrease of trabecular thickness. Moreover, CHH/KS men exhibited lower cortical bone area, whereas total and trabecular areas were higher only at the tibia. Earlier treatment onset (before age 19 years) conferred a significant advantage for trabecular bone volume/tissue volume and trabecular vBMD at the tibia. Conclusion Both vBMD and bone microarchitecture remain impaired in CHH/KS men despite long-term hormonal treatment. Treatment initiation during adolescence is associated with enhanced trabecular outcomes, highlighting the importance of early diagnosis

Clinical and hormonal characteristics of family members.

<p>WT: wild type <i>GNRHR1</i>; TV: mean testicular volume (normal range in post pubertal men: 12–30 mL). MRI: magnetic resonance imaging.</p>a<p>At diagnosis before therapy in affected patients.</p>b<p>Normal range in adults, basal LH: 2.8–7.1 IU/L; basal FSH: 2.4–7.0 IU/L, in post menopausal women: LH: 14–132 IU/L, FSH: 28–171; T in men: 2.8–9.0 ng/mL, Inhibin B in men: 98–366); E2 in women: 24–90 pg/mL (early follicular phase).</p>c<p>GnRH: 100 µg intravenous.</p>d<p>Normal cortisol and GH under hypoglycemia challenge test. Normal free T4 and TSH, normal prolactin.</p><p>- : Not done.</p

Competitive binding characteristics for Pro282Arg and Tyr323Cys <i>hGNRHR1</i> mutants compared to wild type.

<p>COS-7 cells were transfected with the expression vector indicated and then grown in the presence of pharmacoperone (NBI-42902) or vehicle (DMSO), washed and then subjected to competitive binding assays using the GnRH1 analog ([¹²⁵I]-His⁵-D-Tyr⁶-GnRH1) and graded concentrations of unlabeled GnRH1. The degree of mutant receptor binding was compared to cells expressing the wild type receptor.</p

Inositol phosphate accumulation in COS-7 cells expressing wild type <i>GNRHR1</i> and the two <i>hGNRHR1</i> mutants, Pro282Arg and Tyr323Cys.

<p>COS-7 cells were transfected with the expression vector indicated and then grown in the presence of pharmacoperone (NBI-42902) or vehicle (DMSO) and then washed before the addition of myo-[2-³H]Inositol. After 16 h the cells were washed again and then incubated for 1 h with graded concentrations of GnRH1. The amount of intracellular accumulation of labeled inositol phosphates in the two mutant expressing COS-7 cells was compared to cells expressing the wild type receptor.</p

<i>In vitro</i> Radioligand Competition Binding Assay.

<p>Ligand binding affinity (pIC₅₀) were measured on intact COS-7 cells transfected with wild type and mutant receptors by competition binding using ¹²⁵I-His⁵-D-Tyr⁶-GnRH1.</p><p><i>B</i>_max = % of total radioligand bound were expressed relative to wild type receptor without NBI-42902.</p>nb<p>No measurable binding.</p><p>Values are mean ± SEM of three or more independent experiments, converted to nM (in parentheses).</p><p>Significant difference of NBI-42902 treatment on <i>B</i>_max is represented by an asterisk * (p<0.05).</p