Impaired fibroblast growth factor receptor 1 signaling as a cause of normosmic idiopathic hypogonadotropic hypogonadism

Defective FGFR1 Signaling Disrupts Glucose Regulation: Evidence From Humans With FGFR1 Mutations

Context

Activation of fibroblast growth factor receptor 1 (FGFR1) signaling improves the metabolic health of animals and humans, while inactivation leads to diabetes in mice. Direct human genetic evidence for the role of FGFR1 signaling in human metabolic health has not been fully established.

Objective

We hypothesized that individuals with naturally occurring FGFR1 variants ("experiments of nature") will display glucose dysregulation.

Methods

Participants with rare FGFR1 variants and noncarrier controls. Using a recall-by-genotype approach, we examined the β-cell function and insulin sensitivity of 9 individuals with rare FGFR1 deleterious variants compared to 27 noncarrier controls, during a frequently sampled intravenous glucose tolerance test at the Reproductive Endocrine Unit and the Harvard Center for Reproductive Medicine, Massachusetts General Hospital. FGFR1-mutation carriers displayed higher β-cell function in the face of lower insulin sensitivity compared to controls.

Conclusion

These findings suggest that impaired FGFR1 signaling may contribute to an early insulin resistance phase of diabetes pathogenesis and support the candidacy of the FGFR1 signaling pathway as a therapeutic target for improving the human metabolic health.

Gonadotropin-Releasing Hormone Receptor (GnRHR) and Hypogonadotropic Hypogonadism

Human sexual and reproductive development is regulated by the hypothalamic-pituitary-gonadal (HPG) axis, which is primarily controlled by the gonadotropin-releasing hormone (GnRH) acting on its receptor (GnRHR). Dysregulation of the axis leads to conditions such as congenital hypogonadotropic hypogonadism (CHH) and delayed puberty. The pathophysiology of GnRHR makes it a potential target for treatments in several reproductive diseases and in congenital adrenal hyperplasia. GnRHR belongs to the G protein-coupled receptor family and its GnRH ligand, when bound, activates several complex and tissue-specific signaling pathways. In the pituitary gonadotrope cells, it triggers the G protein subunit dissociation and initiates a cascade of events that lead to the production and secretion of the luteinizing hormone (LH) and follicle-stimulating hormone (FSH) accompanied with the phospholipase C, inositol phosphate production, and protein kinase C activation. Pharmacologically, GnRHR can be modulated by synthetic analogues. Such analogues include the agonists, antagonists, and the pharmacoperones. The agonists stimulate the gonadotropin release and lead to receptor desensitization with prolonged use while the antagonists directly block the GnRHR and rapidly reduce the sex hormone production. Pharmacoperones include the most recent GnRHR therapeutic approaches that directly correct the misfolded GnRHRs, which are caused by genetic mutations and hold serious promise for CHH treatment. Understanding of the GnRHR's genomic and protein structure is crucial for the most appropriate assessing of the mutation impact. Such mutations in the GNRHR are linked to normosmic hypogonadotropic hypogonadism and lead to various clinical symptoms, including delayed puberty, infertility, and impaired sexual development. These mutations vary regarding their mode of inheritance and can be found in the homozygous, compound heterozygous, or in the digenic state. GnRHR expression extends beyond the pituitary gland, and is found in reproductive tissues such as ovaries, uterus, and prostate and non-reproductive tissues such as heart, muscles, liver and melanoma cells. This comprehensive review explores GnRHR's multifaceted role in human reproduction and its clinical implications for reproductive disorders.

Whole-Exome Sequencing Identified Rare Genetic Variants Associated with Undervirilized Genitalia in Taiwanese Pediatric Patients

Disorders/differences of sex development (DSDs) are a group of rare and phenotypically variable diseases. The underlying genetic causes of most cases of 46XY DSDs remains unknown. Despite the advent of genetic testing, current investigations of the causes of DSDs allow genetic-mechanism identification in about 20-35% of cases. This study aimed primarily to establish a rapid and high-throughput genetic test for undervirilized males with and without additional dysmorphic features. Routine chromosomal and endocrinological investigations were performed as part of DSD evaluation. We applied whole-exome sequencing (WES) complemented with multiplex ligation-dependent probe amplification to seek explainable genetic causes. Integrated computing programs were used to call and predict the functions of genetic variants. We recruited 20 patients and identified the genetic etiologies for 14 (70%) patients. A total of seven of the patients who presented isolated DSD phenotypes were found to have causative variants in the AR, MAP3K1, and FLNA genes. Moreover, the other seven patients presented additional phenotypes beyond undervirilized genitalia. Among them, two patients were compatible with CHARGE syndrome, one with Robinow syndrome, and another three with hypogonadotropic hypogonadism. One patient, who carried a heterozygous FLNA mutation, also harbored a heterozygous PTPN11 mutation and thus presented some phenotypes of Noonan syndrome. We identified several genetic variants (12 nonsense mutations and one microdeletion) that account for syndromic and nonsyndromic DSDs in the Taiwanese population. The identification of these causative genes extended our current understanding of sex development and related congenital disorders.

Genetic architecture of self-limited delayed puberty and congenital hypogonadotropic hypogonadism

Distinguishing between self limited delayed puberty (SLDP) and congenital hypogonadotropic hypogonadism (CHH) may be tricky as they share clinical and biochemical characteristics. and appear to lie within the same clinical spectrum. However, one is classically transient (SDLP) while the second is typically a lifetime condition (CHH). The natural history and long-term outcomes of these two conditions differ significantly and thus command distinctive approaches and management. Because the first presentation of SDLP and CHH is very similar (delayed puberty with low LH and FSH and low sex hormones), the scientific community is scrambling to identify diagnostic tests that can allow a correct differential diagnosis among these two conditions, without having to rely on the presence or absence of phenotypic red flags for CHH that clinicians anyway seem to find hard to process. Despite the heterogeneity of genetic defects so far reported in DP, genetic analysis through next-generation sequencing technology (NGS) had the potential to contribute to the differential diagnostic process between SLDP and CHH. In this review we will provide an up-to-date overview of the genetic architecture of these two conditions and debate the benefits and the bias of performing genetic analysis seeking to effectively differentiate between these two conditions.

Reversal of idiopathic hypogonadotropic hypogonadism in a Chinese male cohort

Idiopathic hypogonadotropic hypogonadism (IHH) is a rare genetically heterogeneous disease and characterized by incomplete or absent puberty and infertility. It is worth noting that partial IHH patients could recover reproductive endocrine function following treatment, which is termed reversal. This study aimed to investigate clinical and genetic characteristics of IHH reversal patients. A total of 141 IHH male patients were enrolled and followed up regularly. Their clinical and genetic features were collected and analysed to discover something in common in reversal cases. These IHH patients with a median age of 21 years (interquartile range: 18-24) were divided into reversal group (n = 13) and non-reversal group (n = 128). IL17RD, ERBB4, DLX5, EGFR, SEMA4D, B3GNT1 and CCKAR RSVs were demonstrated in reversal cases for the first time. Pathogenic/likely pathogenic (P/LP) RSVs consisted of 3 RSVs (one each patient, including PROKR2 p.W178S, EGFR p.G630R and CCKAR p.S291del) in reversal group. Reversal of IHH could not be ignored in clinical follow-up. Patients with high levels of basal LH and T may harbour more possibility of reversal and worthy extra attention to identify whether reversal occurs or not. Relapse after reversal also needs to be monitored.

Gremlin1 is a therapeutically targetable FGFR1 ligand that regulates lineage plasticity and castration resistance in prostate cancer

Among the greatest hurdles in clinical management of prostate cancer (PCa) are the progression to lethal castration-resistant prostate cancer (CRPC) and the lack of suitable targeted therapies for advanced disease. Here we identify Gremlin1 as a ligand for fibroblast growth factor receptor 1 (FGFR1), which promotes lineage plasticity and drives castration resistance. Importantly, we generate a specific anti-Gremlin1 therapeutic antibody and demonstrate synergistic effect with androgen deprivation therapy (ADT) in CRPC. GREM1 transcription is suppressed by androgen receptor (AR) and released following ADT. We show that Gremlin1 binds to FGFR1 and activates downstream MAPK signaling. Gremlin1 interacts with FGFR1 differently to its canonical ligand FGF1, as revealed through protein structure docking and mutagenesis experiments. Altogether, our data indicate Gremlin1 as a promising candidate therapeutic target for CRPC.

A Novel FGFR1 Missense Mutation in a Portuguese Family with Congenital Hypogonadotropic Hypogonadism

Congenital hypogonadotropic hypogonadism (CHH) is a rare reproductive endocrine disorder characterized by complete or partial failure of pubertal development and infertility due to deficiency of the gonadotropin-releasing hormone (GnRH). CHH has a significant clinical heterogeneity and can be caused by mutations in over 30 genes. The aim of this study was to investigate the genetic defect in two siblings with CHH. A woman with CHH associated with anosmia and her brother with normosmic CHH were investigated by whole exome sequencing. The genetic studies revealed a novel heterozygous missense mutation in the Fibroblast Growth Factor Receptor 1 (FGFR1) gene (NM_023110.3: c.242T>C, p.Ile81Thr) in the affected siblings and in their unaffected father. The mutation affected a conserved amino acid within the first Ig-like domain (D1) of the protein, was predicted to be pathogenic by structure and sequence-based prediction methods, and was absent in ethnically matched controls. These were consistent with a critical role for the identified missense mutation in the activity of the FGFR1 protein. In conclusion, our identification of a novel missense mutation of the FGFR1 gene associated with a variable expression and incomplete penetrance of CHH extends the known mutational spectrum of this gene and may contribute to the understanding of the pathogenesis of CHH.

Genetic Etiology of Idiopathic Hypogonadotropic Hypogonadism

Idiopathic hypogonadotropic hypogonadism (IHH) is a group of rare developmental disorders characterized by low gonadotropin levels in the face of low sex steroid hormone concentrations. IHH is practically divided into two major groups according to the olfactory function: normal sense of smell (normosmia) nIHH, and reduced sense of smell (hyposmia/anosmia) Kallmann syndrome (KS). Although mutations in more than 50 genes have been associated with IHH so far, only half of those cases were explained by gene mutations. Various combinations of deleterious variants in different genes as causes of IHH have been increasingly recognized (Oligogenic etiology). In addition to the complexity of inheritance patterns, the spontaneous or sex steroid-induced clinical recovery from IHH, which is seen in approximately 10–20% of cases, blurs further the phenotype/genotype relationship in IHH, and poses challenging steps in new IHH gene discovery. Beyond helping for clinical diagnostics, identification of the genetic mutations in the pathophysiology of IHH is hoped to shed light on the central governance of the hypothalamo-pituitary-gonadal axis through life stages. This review aims to summarize the genetic etiology of IHH and discuss the clinical and physiological ramifications of the gene mutations.

Genetics of hypogonadotropic Hypogonadism-Human and mouse genes, inheritance, oligogenicity, and genetic counseling

Hypogonadotropic hypogonadism, which may be normosmic (nHH) or anosmic/hyposmic, known as Kallmann syndrome (KS), is due to gonadotropin-releasing hormone deficiency, which results in absent puberty and infertility. Investigation of the genetic basis of nHH/KS over the past 35 years has yielded a substantial increase in our understanding, as variants in 44 genes in OMIM account for ~50% of cases. The first genes for KS (ANOS1) and nHH (GNRHR) were followed by the discovery that FGFR1 variants may cause either nHH or KS. Associated anomalies include midline facial defects, neurologic deficits, cardiac anomalies, and renal agenesis, among others. Mouse models for all but one gene (ANOS1) generally support findings in humans. About half of the known genes implicated in nHH/KS are inherited as autosomal dominant and half are autosomal recessive, whereas only 7% are X-linked recessive. Digenic and oligogenic inheritance has been reported in 2-20% of patients, most commonly with variants in genes that may result in either nHH or KS inherited in an autosomal dominant fashion. In vitro analyses have only been conducted for both gene variants in eight cases and for one gene variant in 20 cases. Rigorous confirmation that two gene variants in the same individual cause the nHH/KS phenotype is lacking for most. Clinical diagnosis is probably best accomplished by targeted next generation sequencing of the known candidate genes with confirmation by Sanger sequencing. Elucidation of the genetic basis of nHH/KS has resulted in an enhanced understanding of this disorder, as well as normal puberty, which makes genetic diagnosis clinically relevant.

Novel FGFR1 Variants Are Associated with Congenital Scoliosis

FGFR1 encodes a transmembrane cytokine receptor, which is involved in the early development of the human embryo and plays an important role in gastrulation, organ specification and patterning of various tissues. Pathogenic FGFR1 variants have been associated with Kallmann syndrome and hypogonadotropic hypogonadism. In our congenital scoliosis (CS) patient series of 424 sporadic CS patients under the framework of the Deciphering disorders Involving Scoliosis and COmorbidities (DISCO) study, we identified four unrelated patients harboring FGFR1 variants, including one frameshift and three missense variants. These variants were predicted to be deleterious by in silico prediction and conservation analysis. Signaling activities and expression levels of the mutated protein were evaluated in vitro and compared to that of the wild type (WT) FGFR1. As a result, the overall protein expressions of c.2334dupC, c.2339T>C and c.1261A>G were reduced to 43.9%, 63.4% and 77.4%, respectively. By the reporter gene assay, we observed significantly reduced activity for c.2334dupC, c.2339T>C and c.1261A>G, indicating the diminished FGFR1 signaling pathway. In conclusion, FGFR1 variants identified in our patients led to only mild disruption to protein function, caused milder skeletal and cardiac phenotypes than those reported previously.

Conditional Fgfr1 Deletion in GnRH Neurons Leads to Minor Disruptions in the Reproductive Axis of Male and Female Mice

In humans and mice, inactivating mutations in fibroblast growth factor receptor 1 (Fgfr1) lead to gonadotropin-releasing hormone (GnRH) deficiency and a host of downstream reproductive disorders. It was unclear if Fgfr1 signaling directly upon GnRH neurons critically drove the establishment of a functional GnRH system. To answer this question, we generated a mouse model with a conditional deletion of Fgfr1 in GnRH neurons using the Cre/loxP approach. These mice, called Fgfr1cKO mice, were examined along with control mice for their pubertal onset and a host of reproductive axis functions. Our results showed that Fgfr1cKO mice harbored no detectable defects in the GnRH system and pubertal onset, suffered only subtle changes in the pituitary function, but exhibited significantly disrupted testicular and ovarian morphology at 25 days of age, indicating impaired gametogenesis at a young age. However, these disruptions were transient and became undetectable in older mice. Our results suggest that Fgfr1 signaling directly on GnRH neurons supports, to some extent, the reproductive axis function in the period leading to the early phase of puberty, but is not critically required for pubertal onset or reproductive maintenance in sexually mature animals.

Whole exome sequencing and trio analysis to broaden the variant spectrum of genes in idiopathic hypogonadotropic hypogonadism

Dozens of genes are associated with idiopathic hypogonadotropic hypogonadism (IHH) and an oligogenic etiology has been suggested. However, the associated genes may account for only approximately 50% cases. In addition, a genomic systematic pedigree analysis is still lacking. Here, we conducted whole exome sequencing (WES) on 18 unrelated men affected by IHH and their corresponding parents. Notably, one reported and 10 novel variants in eight known IHH causative genes (AXL, CCDC141, CHD7, DMXL2, FGFR1, PNPLA6, POLR3A, and PROKR2), nine variants in nine recently reported candidate genes (DCAF17, DCC, EGF, IGSF10, NOTCH1, PDE3A, RELN, SLIT2, and TRAPPC9), and four variants in four novel candidate genes for IHH (CCDC88C, CDON, GADL1, and SPRED3) were identified in 77.8% (14/18) of IHH cases. Among them, eight (8/18, 44.4%) cases carried more than one variant in IHH-related genes, supporting the oligogenic model. Interestingly, we found that those variants tended to be maternally inherited (maternal with n = 17 vs paternal with n = 7; P = 0.028). Our further retrospective investigation of published reports replicated the maternal bias (maternal with n = 46 vs paternal with n = 28; P = 0.024). Our study extended a variant spectrum for IHH and provided thefirst evidence that women are probably more tolerant to variants of IHH-related genes than men.

Exploring the Genetic Diversity of Isolated Hypogonadotropic Hypogonadism and Its Phenotypic Spectrum: A Case Series

Background:

Isolated hypogonadotropic hypogonadism (IHH) is a rare disorder being classified as Kallmann syndrome (KS). The present study was conducted to study the genotype and relative proportion of different genetic mutations in IHH and to assess its correlation with phenotype.

Methods:

Eleven consecutive subjects presenting to the Department of Endocrinology were retrospectively analyzed during May 2017 to December 2018 with IHH. Phenotypic features and hormonal studies were analyzed along with clinical exome by targeted gene sequencing (Next generation sequencing). Thirty-nine relevant genes were tested in the analysis.

Results:

Of the 11 patients studied, five had KS and six had nIHH. At diagnosis, mean chronological age was 25 years. There were associated anomalies in KS group including bimanual synkinesia (n=2), unilateral renal agenesis (n=1) and submucosal cleft palate (n=1). Absence or hypoplasia of the olfactory bulb/sulci was found in 4/5 patients with KS. Genetic mutations in KAL1, CHD7, FGFR1, GNRHR, PROKR2, HS6ST1 genes were found in nine of the eleven subjects. Of the five subjects with KS, two had mutations in KAL1 gene. Two siblings who had bimanual synkinesia had CHD7 mutation. The genotype of nIHH subjects (n=6) was more heterogeneous.

Conclusion:

This study analyzed the clinical, endocrinological, and genetic features in IHH patients. Detectable genetic mutations were seen in a large proportion of cases. A considerable heterogeneity was seen in the genotype with new variants detected. A definite correlation of phenotype-genotype was not possible, and significant overlap was seen between CHD7 and KAl1, and FGFR1 phenotypes.

Dizygotic twin sisters with normosmic idiopathic hypogonadotropic hypogonadism caused by an FGFR1 gene variant

Isolated hypogonadotropic hypogonadism (IHH) is a rare genetic disorder that is clinically and genetically heterogeneous. It is characterized by absent or incomplete pubertal development owing to an isolated defect in the production, secretion, or action of gonadotropin-releasing hormone. The incidence of IHH is estimated at 1:30,000 in males and 1:125,000 in females. Although the vast majority of IHH cases are sporadic, some X-linked recessive, autosomal dominant, and autosomal recessive modes of inheritance have been described. IHH can be classified into Kallmann syndrome with anosmia and normosmic IHH. Here, we report dizygotic twin sisters with normosmic IHH who showed short stature and absence of puberty as a result of a variant of the FGFR1 gene. They had a normal sense of smell, and brain magnetic resonance imaging (MRI) showed well-defined olfactory bulbs. The older sister and the twins' mother had cleft palate, while the younger sister did not. The mother had menarche at the age of 16 years after hormonal replacement owing to delayed puberty. Molecular analysis of the FGFR1 gene identified a missense variant c.874C>G (p.His292Asp) in the twins and their mother. Herein, we described the clinical heterogeneity observed in the 2 affected twins who carry an identical variant in the FGFR1 gene. Further studies of the effects of modifier genes and epigenetic factors on the expression of FGFR1, as well as the various clinical manifestations of its mutations, are warranted.

Combined in vitro and in silico analyses of FGFR1 variants: genotype-phenotype study in idiopathic hypogonadotropic hypogonadism

Fibroblast growth factor receptor 1 (FGFR1) is an idiopathic hypogonadotropic hypogonadism (IHH)-associated gene, mutated in approximately 10% of the patients with this condition. Through targeted gene sequencing of 153 males with IHH and 100 healthy controls, we identified 10 mutations in FGFR1 from IHH patients with a frequency of 5.9% in the Chinese population of central China. These included nine missense mutations(NM_023110.2, p.Gly687Arg, p.Ala608Asp, p.Gly348Glu, p.Asn296Ser, p.Gly226Asp, p.Arg209Cys, p.Gly97Arg, p.Val71Met, p.Gly70Arg) and a splicing mutation c.1430 + 1G > T. in vitro and in silico analyses of FGFR1 variants were conducted to study the impact of the identified mutations. Our findings indicated that the splicing mutation dramatically affected premRNA processing, causing exon 10 and 6 nucleotides in the 3' end of exon 9 to be completely skipped. Two variants (p.Gly687Arg and p.Ala608Asp) markedly impaired tyrosine kinase activity, while the other variants had limited impact on the mitogen-activated protein kinase (MAPK) signaling pathway. However, the functional impairment of the mutant receptors was not always consistent with the phenotypes, indicating that FGFR1 mutations might cause IHH in conjunction with other mutant genes. In this study, we expanded the knowledge on the mutation spectrum of FGFR1 in IHH patients and explored the genotype-phenotype relationship.

Functional Characteristics of Novel FGFR1 Mutations in Patients with Isolated Gonadotropin-Releasing Hormone Deficiency

BACKGROUND

Isolated gonadotropin-releasing hormone (GnRH) deficiency (IGD) has a wide phenotypic spectrum including Kallmann syndrome (KS) and normosmic idiopathic hypogonadotropic hypogonadism (nIHH). FGFR1 mutations have been identified in 3-10% of patients with KS or nIHH. This study was performed to investigate clinical phenotypes and functional characteristics of FGFR1 mutations in patients with IGD.

METHODS

This study included 8 patients (from 7 families) with FGFR1 mutations identified by targeted gene panel sequencing or whole exome sequencing (WES). The impact of the identified mutations on FGFR1 function was assessed using in vitro studies.

RESULTS

Seven heterozygous mutations in FGFR1 were identified in 8 patients from 7 independent families. The patients exhibited a wide spectrum of pubertal development, including anosmia in a prepubertal boy (n=1), delayed puberty (n=2), nIHH (n=3), and KS (n=2). Four of the mutations were classified as likely pathogenic, and the other three were variants of uncertain significance. FGF8-FGFR1 signaling activities for the novel FGFR1 variants (p.Y339H, p.S681I, and p.N185Kfs*16) were reduced by in vitro functional assay, indicating loss-of-function mutations.

CONCLUSIONS

This study identified seven rare sequence variants in FGFR1 in patients with KS and nIHH. Probands with an FGFR1 mutations displayed a wide phenotypic spectrum ranging from KS to anosmia. A prepubertal male with anosmia should be followed up to assess pubertal development because they can manifest hypogonadotropic hypogonadism after puberty. These results expand the phenotypic spectrum of FGFR1 mutations and suggest a broader biologic role of FGFR1 in reproduction.

Neuron-Derived Neurotrophic Factor Is Mutated in Congenital Hypogonadotropic Hypogonadism

Congenital hypogonadotropic hypogonadism (CHH) is a rare genetic disorder characterized by infertility and the absence of puberty. Defects in GnRH neuron migration or altered GnRH secretion and/or action lead to a severe gonadotropin-releasing hormone (GnRH) deficiency. Given the close developmental association of GnRH neurons with the olfactory primary axons, CHH is often associated with anosmia or hyposmia, in which case it is defined as Kallmann syndrome (KS). The genetics of CHH are heterogeneous, and >40 genes are involved either alone or in combination. Several CHH-related genes controlling GnRH ontogeny encode proteins containing fibronectin-3 (FN3) domains, which are important for brain and neural development. Therefore, we hypothesized that defects in other FN3-superfamily genes would underlie CHH. Next-generation sequencing was performed for 240 CHH unrelated probands and filtered for rare, protein-truncating variants (PTVs) in FN3-superfamily genes. Compared to gnomAD controls the CHH cohort was statistically enriched for PTVs in neuron-derived neurotrophic factor (NDNF) (p = 1.40 × 10^-6). Three heterozygous PTVs (p.Lys62^∗, p.Tyr128Thrfs^∗55, and p.Trp469^∗, all absent from the gnomAD database) and an additional heterozygous missense mutation (p.Thr201Ser) were found in four KS probands. Notably, NDNF is expressed along the GnRH neuron migratory route in both mouse embryos and human fetuses and enhances GnRH neuron migration. Further, knock down of the zebrafish ortholog of NDNF resulted in altered GnRH migration. Finally, mice lacking Ndnf showed delayed GnRH neuron migration and altered olfactory axonal projections to the olfactory bulb; both results are consistent with a role of NDNF in GnRH neuron development. Altogether, our results highlight NDNF as a gene involved in the GnRH neuron migration implicated in KS.

Genetic Evaluation of Patients With Delayed Puberty and Congenital Hypogonadotropic Hypogonadism: Is it Worthy of Consideration?

Delayed puberty is a common reason of pediatric endocrinological consultation. It is often a self-limited (or constitutional) condition with a strong familial basis. The type of inheritance is variable but most commonly autosomal dominant. Despite this strong genetic determinant, mutations in genes implicated in the regulation of hypothalamic-pituitary-gonadal axis have rarely been identified in cases of self-limited delayed puberty and often in relatives of patients with congenital hypogonadotropic hypogonadism (i.e., FGFR1 and GNRHR genes). However, recently, next-generation sequencing analysis has led to the discovery of new genes (i.e., IGSF10, HS6ST1, FTO, and EAP1) that are implicated in determining isolated self-limited delayed puberty in some families. Despite the heterogeneity of genetic defects resulting in delayed puberty, genetic testing may become a useful diagnostic tool for the correct classification and management of patients with delayed puberty. This article will discuss the benefits and the limitations of genetic testing execution in cases of delayed puberty.

Genetic causes of hypopituitarism

Hypopituitarism in neonates is rare, but has life-threatening complications if untreated. This review describes the features of hypopituitarism and the evidence for which infants in whom a genetic cause should be suspected. Importantly, neonates are often asymptomatic or present with non-specific symptoms. Hypopituitarism can be due to abnormal gland development as a result of genetic defects, which result from mutations in gene coding for transcription factors which regulate pituitary development. The mutations can be divided into those causing isolated hypopituitarism or those causing syndromes with associated hypopituitarism. The latter involve mutations in transcription factors which regulate pituitary, as well as extra-pituitary development. There is a paucity of evidence as to which patients should be investigated for genetic mutations, but detailed clinical and biochemical phenotyping with magnetic resonance imaging of the pituitary gland could help target those in whom genetic investigations would be most appropriate.

Clinical Management of Congenital Hypogonadotropic Hypogonadism

The initiation and maintenance of reproductive capacity in humans is dependent on pulsatile secretion of the hypothalamic hormone GnRH. Congenital hypogonadotropic hypogonadism (CHH) is a rare disorder that results from the failure of the normal episodic GnRH secretion, leading to delayed puberty and infertility. CHH can be associated with an absent sense of smell, also termed Kallmann syndrome, or with other anomalies. CHH is characterized by rich genetic heterogeneity, with mutations in >30 genes identified to date acting either alone or in combination. CHH can be challenging to diagnose, particularly in early adolescence where the clinical picture mirrors that of constitutional delay of growth and puberty. Timely diagnosis and treatment will induce puberty, leading to improved sexual, bone, metabolic, and psychological health. In most cases, patients require lifelong treatment, yet a notable portion of male patients (∼10% to 20%) exhibit a spontaneous recovery of their reproductive function. Finally, fertility can be induced with pulsatile GnRH treatment or gonadotropin regimens in most patients. In summary, this review is a comprehensive synthesis of the current literature available regarding the diagnosis, patient management, and genetic foundations of CHH relative to normal reproductive development.

KLB, encoding β-Klotho, is mutated in patients with congenital hypogonadotropic hypogonadism

Congenital hypogonadotropic hypogonadism (CHH) is a rare genetic form of isolated gonadotropin‐releasing hormone (GnRH) deficiency caused by mutations in > 30 genes. Fibroblast growth factor receptor 1 (FGFR1) is the most frequently mutated gene in CHH and is implicated in GnRH neuron development and maintenance. We note that a CHH FGFR1 mutation (p.L342S) decreases signaling of the metabolic regulator FGF21 by impairing the association of FGFR1 with β‐Klotho (KLB), the obligate co‐receptor for FGF21. We thus hypothesized that the metabolic FGF21/KLB/FGFR1 pathway is involved in CHH. Genetic screening of 334 CHH patients identified seven heterozygous loss‐of‐function KLB mutations in 13 patients (4%). Most patients with KLB mutations (9/13) exhibited metabolic defects. In mice, lack of Klb led to delayed puberty, altered estrous cyclicity, and subfertility due to a hypothalamic defect associated with inability of GnRH neurons to release GnRH in response to FGF21. Peripheral FGF21 administration could indeed reach GnRH neurons through circumventricular organs in the hypothalamus. We conclude that FGF21/KLB/FGFR1 signaling plays an essential role in GnRH biology, potentially linking metabolism with reproduction.

GENETICS IN ENDOCRINOLOGY: Genetic counseling for congenital hypogonadotropic hypogonadism and Kallmann syndrome: new challenges in the era of oligogenism and next-generation sequencing

Congenital hypogonadotropic hypogonadism (CHH) and Kallmann syndrome (KS) are rare, related diseases that prevent normal pubertal development and cause infertility in affected men and women. However, the infertility carries a good prognosis as increasing numbers of patients with CHH/KS are now able to have children through medically assisted procreation. These are genetic diseases that can be transmitted to patients' offspring. Importantly, patients and their families should be informed of this risk and given genetic counseling. CHH and KS are phenotypically and genetically heterogeneous diseases in which the risk of transmission largely depends on the gene(s) responsible(s). Inheritance may be classically Mendelian yet more complex; oligogenic modes of transmission have also been described. The prevalence of oligogenicity has risen dramatically since the advent of massively parallel next-generation sequencing (NGS) in which tens, hundreds or thousands of genes are sequenced at the same time. NGS is medically and economically more efficient and more rapid than traditional Sanger sequencing and is increasingly being used in medical practice. Thus, it seems plausible that oligogenic forms of CHH/KS will be increasingly identified making genetic counseling even more complex. In this context, the main challenge will be to differentiate true oligogenism from situations when several rare variants that do not have a clear phenotypic effect are identified by chance. This review aims to summarize the genetics of CHH/KS and to discuss the challenges of oligogenic transmission and also its role in incomplete penetrance and variable expressivity in a perspective of genetic counseling.

Update on the Genetics of Idiopathic Hypogonadotropic Hypogonadism

Traditionally, idiopathic hypogonadotropic hypogonadism (IHH) is divided into two major categories: Kallmann syndrome (KS) and normosmic IHH (nIHH). To date, inactivating variants in more than 50 genes have been reported to cause IHH. These mutations are estimated to account for up to 50% of all apparently hereditary cases. Identification of further causative gene mutations is expected to be more feasible with the increasing use of whole exome/genome sequencing. Presence of more than one IHH-associated mutant gene in a given patient/pedigree (oligogenic inheritance) is seen in 10-20% of all IHH cases. It is now well established that about 10-20% of IHH cases recover from IHH either spontaneously or after receiving some sex steroid replacement therapy. Moreover, there may be an overlap or transition between constitutional delay in growth and puberty (CDGP) and IHH. It has been increasingly observed that oligogenic inheritance and clinical recovery complicates the phenotype/genotype relationship in IHH, thus making it challenging to find new IHH-associated genes. In a clinical sense, recognizing those IHH genes and associated phenotypes may improve our diagnostic capabilities by enabling us to prioritize the screening of particular gene(s) such as synkinesia (ANOS1), dental agenesis (FGF8/FGFR1) and hearing loss (CHD7). Also, IHH-associated gene studies may be translated into new therapies such as for polycystic ovary syndrome. In a scientific sense, the most significant contribution of IHH-associated gene studies has been the characterization of the long-sought gonadotropin releasing hormone pulse generator. It appears that genetic studies of IHH will continue to advance our knowledge in both the biological and clinical domains.

Withdrawn: Discovering Genes Essential to the Hypothalamic Regulation of Human Reproduction Using a Human Disease Model: Adjusting to Life in the "-Omics" Era

The neuroendocrine regulation of reproduction is an intricate process requiring the exquisite coordination of an assortment of cellular networks, all converging on the GnRH neurons. These neurons have a complex life history, migrating mainly from the olfactory placode into the hypothalamus, where GnRH is secreted and acts as the master regulator of the hypothalamic-pituitary-gonadal axis. Much of what we know about the biology of the GnRH neurons has been aided by discoveries made using the human disease model of isolated GnRH deficiency (IGD), a family of rare Mendelian disorders that share a common failure of secretion and/or action of GnRH causing hypogonadotropic hypogonadism. Over the last 30 years, research groups around the world have been investigating the genetic basis of IGD using different strategies based on complex cases that harbor structural abnormalities or single pleiotropic genes, endogamous pedigrees, candidate gene approaches as well as pathway gene analyses. Although such traditional approaches, based on well-validated tools, have been critical to establish the field, new strategies, such as next-generation sequencing, are now providing speed and robustness, but also revealing a surprising number of variants in known IGD genes in both patients and healthy controls. Thus, before the field moves forward with new genetic tools and continues discovery efforts, we must reassess what we know about IGD genetics and prepare to hold our work to a different standard. The purpose of this review is to: 1) look back at the strategies used to discover the "known" genes implicated in the rare forms of IGD; 2) examine the strengths and weaknesses of the methodologies used to validate genetic variation; 3)substantiate the role of known genes in the pathophysiology of the disease; and 4) project forward as we embark upon a widening use of these new and powerful technologies for gene discovery. (Endocrine Reviews 36: 603-621, 2015).

Genetic testing facilitates prepubertal diagnosis of congenital hypogonadotropic hypogonadism

Neonatal micropenis and cryptorchidism raise the suspicion of congenital hypogonadotropic hypogonadism (CHH), a rare genetic disorder caused by gonadotropin-releasing hormone deficiency. Low plasma testosterone levels and low gonadotropins during minipuberty provide a clinical diagnostic clue, yet these tests are seldomly performed in general practice. We report a male neonate with no family history of reproductive disorders who was born with micropenis and cryptorchidism. Hormonal testing at age 2.5 months showed low testosterone (0.3 nmol/L) and undetectable gonadotropins (luteinizing hormone and follicle-stimulating hormone both <0.5 U/L), suggestive of CHH. Genetic testing identified a de novo, heterozygous mutation in fibroblast growth factor receptor 1 (FGFR1 p.L630P). L630 resides on the ATP binding cleft of the FGFR1 tyrosine kinase domain, and L630P is predicted to cause a complete loss of receptor function. Cell-based assays confirmed that L630P abolishes FGF8 signaling activity. Identification of a loss-of-function de novo FGFR1 mutation in this patient confirms the diagnosis of CHH, allowing for a timely hormonal treatment to induce pubertal development. Therefore, genetic testing can complement clinical and hormonal assessment for a timely diagnosis of CHH in childhood.

Variants in congenital hypogonadotrophic hypogonadism genes identified in an Indonesian cohort of 46,XY under-virilised boys

Background

Congenital hypogonadotrophic hypogonadism (CHH) and Kallmann syndrome (KS) are caused by disruption to the hypothalamic-pituitary-gonadal (H-P-G) axis. In particular, reduced production, secretion or action of gonadotrophin-releasing hormone (GnRH) is often responsible. Various genes, many of which play a role in the development and function of the GnRH neurons, have been implicated in these disorders. Clinically, CHH and KS are heterogeneous; however, in 46,XY patients, they can be characterised by under-virilisation phenotypes such as cryptorchidism and micropenis or delayed puberty. In rare cases, hypospadias may also be present.

Results

Here, we describe genetic mutational analysis of CHH genes in Indonesian 46,XY disorder of sex development patients with under-virilisation. We present 11 male patients with varying degrees of under-virilisation who have rare variants in known CHH genes. Interestingly, many of these patients had hypospadias.

Conclusions

We postulate that variants in CHH genes, in particular PROKR2, PROK2, WDR11 and FGFR1 with CHD7, may contribute to under-virilisation phenotypes including hypospadias in Indonesia.

Spectrum of phenotype and genotype of congenital isolated hypogonadotropic hypogonadism in Asian Indians

BACKGROUND

Congenital isolated hypogonadotropic hypogonadism (IHH) is caused due to defect in GnRH neuronal development, migration and action. Although genetic aetiology of IHH is increasingly being studied, Asian Indian data on phenotypic spectrum and genetic basis are scarce.

OBJECTIVE

To investigate the phenotypic and genotypic spectrum of IHH in Asian Indian subjects.

DESIGN, SETTING AND SUBJECTS

A cohort of 135 IHH probands were characterized phenotypically for reproductive and nonreproductive features and screened for rare sequence variations (RSVs) in five genes KAL1, FGFR1, FGF8, GNRHR and KISS1R.

RESULT

Of 135 probands [56 normosmic IHH (nIHH) and 79 Kallmann syndrome (KS)], 20 were familial cases. KS group had more male dominance (M:F ratio of 8:1) as compared to nIHH group (M:F ratio of 1·5:1). Complete absence of puberty was more prevalent in KS probands (81% in KS vs 46% in nIHH). The prevalence of MRI abnormalities was more in anosmic group (92·8%) as compared to hyposmic (37·5%) and normosmic groups (15·4%). No particular nonreproductive phenotypic predominance was seen in any group. Genotyping revealed rare sequence variation (RSV) detection rate of 15·5% in five genes studied: (KAL1 - 4·4%, FGFR1 - 4·4%, GNRHR - 6·7%, oligogenicity - 1·5%). Prevalence of RSV was more common in familial cases (35%) as compared to sporadic (12·2%). GNRHR RSV p.C279Y (not reported in patients of ethnicities other than south Asians) was recurring in four unrelated patients.

CONCLUSION

In our cohort, 60% were KS with majority of males and a severe reproductive phenotype as against nIHH. Contribution of the genetic burden for the five genes studied was 15·5%. RSV p.C279Y in GNRHR may have a founder effect originating from south Asia. This study provides a model for molecular and phenotypic representation of Asian Indian subjects with IHH.

MANAGEMENT OF ENDOCRINE DISEASE: Reversible hypogonadotropic hypogonadism

Congenital hypogonadotropic hypogonadism (CHH) is characterized by lack of puberty and infertility. Traditionally, it has been considered a life-long condition yet cases of reversibility have been described wherein patients spontaneously recover function of the reproductive axis following treatment. Reversibility occurs in both male and female CHH cases and appears to be more common (~10-15%) than previously thought. These reversal patients span a range of GnRH deficiency from mild to severe and many reversal patients harbor mutations in genes underlying CHH. However, to date there are no clear factors for predicting reversible CHH. Importantly, recovery of reproductive axis function may not be permanent. Thus, CHH is not always life-long and the incidence of reversal warrants periodic treatment withdrawal with close monitoring and follow-up. Reversible CHH highlights the importance of environmental (epigenetic) factors such as sex steroid treatment on the reproductive axis in modifying the phenotype. This review provides an overview and an update on what is known about this phenomenon.

Molecular Plasticity of Male and Female Murine Gonadotropes Revealed by mRNA Sequencing

Gonadotropes in the anterior pituitary gland are of particular importance within the hypothalamic-pituitary-gonadal axis because they provide a means of communication and thus a functional link between the brain and the gonads. Recent results indicate that female gonadotropes may be organized in the form of a network that shows plasticity and adapts to the altered endocrine conditions of different physiological states. However, little is known about functional changes on the molecular level within gonadotropes during these different conditions. In this study we capitalize on a binary genetic strategy in order to fluorescently label murine gonadotrope cells. Using this mouse model allows to produce an enriched gonadotrope population using fluorescence activated cell sorting to perform mRNA sequencing. By using this strategy, we analyze and compare the expression profile of murine gonadotropes in different genders and developmental and hormonal stages. We find that gonadotropes taken from juvenile males and females, from cycling females at diestrus and at proestrus, from lactating females, and from adult males each have unique gene expression patterns with approximately 100 to approximately 500 genes expressed only in one particular stage. We also demonstrate extensive gene-expression profile changes with up to approximately 2200 differentially expressed genes when comparing female and male development, juveniles and adults, and cycling females. Differentially expressed genes were significantly enriched in the GnRH signaling, calcium signaling, and MAPK signaling pathways by Kyoto Encyclopedia of Genes and Genomes analysis. Our data provide an unprecedented molecular view of the primary gonadotropes and reveal a high degree of molecular plasticity within the gonadotrope population.

Dominant-negative kinase domain mutations in FGFR1 can explain the clinical severity of Hartsfield syndrome

Mutations in FGFR1 have recently been associated with Hartsfield syndrome, a clinically distinct syndromic form of holoprosencephaly (HPE) with ectrodactly, which frequently includes combinations of craniofacial, limb and brain abnormalities not typical for classical HPE. Unrelated clinical conditions generally without craniofacial or multi-system malformations include Kallmann syndrome and idiopathic hypogonadotropic hypogonadism. FGFR1 is a principal cause for these less severe diseases as well. Here we demonstrate that of the nine FGFR1 mutations recently detected in our screen of over 200 HPE probands by next generation sequencing, only five distinct mutations in the kinase domain behave as dominant-negative mutations in zebrafish over-expression assays. Three FGFR1 mutations seen in HPE probands behave identical to wild-type FGFR1 in rescue assays, including one apparent de novo variation. Interestingly, in one HPE family, a deleterious FGFR1 allele was transmitted from one parent and a loss-of-function allele in FGF8 from the other parent to both affected daughters. This family is one of the clearest examples to date of gene:gene synergistic interactions causing HPE in humans.

Withdrawn: Discovering Genes Essential to the Hypothalamic Regulation of Human Reproduction Using a Human Disease Model: Adjusting to Life in the "-Omics" Era

The neuroendocrine regulation of reproduction is an intricate process requiring the exquisite coordination of an assortment of cellular networks, all converging on the GnRH neurons. These neurons have a complex life history, migrating mainly from the olfactory placode into the hypothalamus, where GnRH is secreted and acts as the master regulator of the hypothalamic-pituitary-gonadal axis. Much of what we know about the biology of the GnRH neurons has been aided by discoveries made using the human disease model of isolated GnRH deficiency (IGD), a family of rare Mendelian disorders that share a common failure of secretion and/or action of GnRH causing hypogonadotropic hypogonadism. Over the last 30 years, research groups around the world have been investigating the genetic basis of IGD using different strategies based on complex cases that harbor structural abnormalities or single pleiotropic genes, endogamous pedigrees, candidate gene approaches as well as pathway gene analyses. Although such traditional approaches, based on well-validated tools, have been critical to establish the field, new strategies, such as next-generation sequencing, are now providing speed and robustness, but also revealing a surprising number of variants in known IGD genes in both patients and healthy controls. Thus, before the field moves forward with new genetic tools and continues discovery efforts, we must reassess what we know about IGD genetics and prepare to hold our work to a different standard. The purpose of this review is to: 1) look back at the strategies used to discover the "known" genes implicated in the rare forms of IGD; 2) examine the strengths and weaknesses of the methodologies used to validate genetic variation; 3)substantiate the role of known genes in the pathophysiology of the disease; and 4) project forward as we embark upon a widening use of these new and powerful technologies for gene discovery. (Endocrine Reviews 36: 603-621, 2015).

Discovering Genes Essential to the Hypothalamic Regulation of Human Reproduction Using a Human Disease Model: Adjusting to Life in the "-Omics" Era

The neuroendocrine regulation of reproduction is an intricate process requiring the exquisite coordination of an assortment of cellular networks, all converging on the GnRH neurons. These neurons have a complex life history, migrating mainly from the olfactory placode into the hypothalamus, where GnRH is secreted and acts as the master regulator of the hypothalamic-pituitary-gonadal axis. Much of what we know about the biology of the GnRH neurons has been aided by discoveries made using the human disease model of isolated GnRH deficiency (IGD), a family of rare Mendelian disorders that share a common failure of secretion and/or action of GnRH causing hypogonadotropic hypogonadism. Over the last 30 years, research groups around the world have been investigating the genetic basis of IGD using different strategies based on complex cases that harbor structural abnormalities or single pleiotropic genes, endogamous pedigrees, candidate gene approaches as well as pathway gene analyses. Although such traditional approaches, based on well-validated tools, have been critical to establish the field, new strategies, such as next-generation sequencing, are now providing speed and robustness, but also revealing a surprising number of variants in known IGD genes in both patients and healthy controls. Thus, before the field moves forward with new genetic tools and continues discovery efforts, we must reassess what we know about IGD genetics and prepare to hold our work to a different standard. The purpose of this review is to: 1) look back at the strategies used to discover the "known" genes implicated in the rare forms of IGD; 2) examine the strengths and weaknesses of the methodologies used to validate genetic variation; 3) substantiate the role of known genes in the pathophysiology of the disease; and 4) project forward as we embark upon a widening use of these new and powerful technologies for gene discovery.

Bone involvement in males with Kallmann disease

BACKGROUND

Kallmann syndrome (KS) is a rare genetic condition characterized by congenital early-onset hypogonadotropic hypogonadism and anosmia or hyposmia. Male subjects are more frequently affected and present absent/delayed puberty, low testosterone levels with higher risk for osteoporosis. Therefore, to maintain normal levels of sex steroids and prevent bone loss, male KS needs life-long hormonal replacement therapy (HRT).

AIMS

The objective of our study is to assess bone involvement in subjects with KS currently treated with HRT.

METHODS

In our retrospective study, we analyzed data from medical records of patients with KS treated with HRT (either gonadotropins or testosterone preparations), including clinical history, biochemical parameters, and the following outcome measures: the bone mineral density (BMD) at the lumbar spine (LS), femoral neck (FN), and total body less head (TBLH); and the Vertebral Fracture Assessment (VFA) by Dual Energy X-ray Absorptiometry (DXA).

RESULTS

Clinical and instrumental data of 32 patients with KS were evaluated; their mean age was 30.32 (± 10.09) years, their mean body mass index (BMI) was 25.71 (± 3.23) kg/m(2). Four patients (12.5%) had a LS BMD Z score below the expected range for age. Five patients had vertebral deformities observed at VFA. Duration of HRT was related to bone health parameters: BMD at all measured sites were higher in patients receiving adequate HRT for more than 2 years compared with the patients treated for less than 6 months. A deficient vitamin D status was found in 43% of cases and it was prevalent in patients with shorter HRT.

DISCUSSION AND CONCLUSION

Early starting and adequate duration of HRT are related to bone health parameters in patients with congenital hypogonadotropic hypogonadism due to KS. Restoring vitamin D sufficiency might also be advisable in this condition.

Novel FGFR1 mutations in Kallmann syndrome and normosmic idiopathic hypogonadotropic hypogonadism: evidence for the involvement of an alternatively spliced isoform

OBJECTIVE

To determine the prevalence of fibroblast growth factor receptor 1 (FGFR1) mutations and their predicted functional consequences in patients with idiopathic hypogonadotropic hypogonadism (IHH).

DESIGN

Cross-sectional study.

SETTING

Multicentric.

PATIENT(S)

Fifty unrelated patients with IHH (21 with Kallmann syndrome and 29 with normosmic IHH).

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Patients were screened for mutations in FGFR1. The functional consequences of mutations were predicted by in silico structural and conservation analysis.

RESULT(S)

Heterozygous FGFR1 mutations were identified in six (12%) kindreds. These consisted of frameshift mutations (p.Pro33-Alafs*17 and p.Tyr654*) and missense mutations in the signal peptide (p.Trp4Cys), in the D1 extracellular domain (p.Ser96Cys) and in the cytoplasmic tyrosine kinase domain (p.Met719Val). A missense mutation was identified in the alternatively spliced exon 8A (p.Ala353Thr) that exclusively affects the D3 extracellular domain of FGFR1 isoform IIIb. Structure-based and sequence-based prediction methods and the absence of these variants in 200 normal controls were all consistent with a critical role for the mutations in the activity of the receptor. Oligogenic inheritance (FGFR1/CHD7/PROKR2) was found in one patient.

CONCLUSION(S)

Two FGFR1 isoforms, IIIb and IIIc, result from alternative splicing of exons 8A and 8B, respectively. Loss-of-function of isoform IIIc is a cause of IHH, whereas isoform IIIb is thought to be redundant. Ours is the first report of normosmic IHH associated with a mutation in the alternatively spliced exon 8A and suggests that this disorder can be caused by defects in either of the two alternatively spliced FGFR1 isoforms.

FGFR1 and PROKR2 rare variants found in patients with combined pituitary hormone deficiencies

The genetic aetiology of congenital hypopituitarism (CH) is not entirely elucidated. FGFR1 and PROKR2 loss-of-function mutations are classically involved in hypogonadotrophic hypogonadism (HH), however, due to the clinical and genetic overlap of HH and CH; these genes may also be involved in the pathogenesis of CH. Using a candidate gene approach, we screened 156 Brazilian patients with combined pituitary hormone deficiencies (CPHD) for loss-of-function mutations in FGFR1 and PROKR2. We identified three FGFR1 variants (p.Arg448Trp, p.Ser107Leu and p.Pro772Ser) in four unrelated patients (two males) and two PROKR2 variants (p.Arg85Cys and p.Arg248Glu) in two unrelated female patients. Five of the six patients harbouring the variants had a first-degree relative that was an unaffected carrier of it. Results of functional studies indicated that the new FGFR1 variant p.Arg448Trp is a loss-of-function variant, while p.Ser107Leu and p.Pro772Ser present signalling activity similar to the wild-type form. Regarding PROKR2 variants, results from previous functional studies indicated that p.Arg85Cys moderately compromises receptor signalling through both MAPK and Ca(2) (+) pathways while p.Arg248Glu decreases calcium mobilization but has normal MAPK activity. The presence of loss-of-function variants of FGFR1 and PROKR2 in our patients with CPHD is indicative of an adjuvant and/or modifier effect of these rare variants on the phenotype. The presence of the same variants in unaffected relatives implies that they cannot solely cause the phenotype. Other associated genetic and/or environmental modifiers may play a role in the aetiology of this condition.

A shared genetic basis for self-limited delayed puberty and idiopathic hypogonadotropic hypogonadism

CONTEXT

Delayed puberty (DP) is a common issue and, in the absence of an underlying condition, is typically self limited. Alhough DP seems to be heritable, no specific genetic cause for DP has yet been reported. In contrast, many genetic causes have been found for idiopathic hypogonadotropic hypogonadism (IHH), a rare disorder characterized by absent or stalled pubertal development.

OBJECTIVE

The objective of this retrospective study, conducted at academic medical centers, was to determine whether variants in IHH genes contribute to the pathogenesis of DP.

SUBJECTS AND OUTCOME MEASURES

Potentially pathogenic variants in IHH genes were identified in two cohorts: 1) DP family members of an IHH proband previously found to have a variant in an IHH gene, with unaffected family members serving as controls, and 2) DP individuals with no family history of IHH, with ethnically matched control subjects drawn from the Exome Aggregation Consortium.

RESULTS

In pedigrees with an IHH proband, the proband's variant was shared by 53% (10/19) of DP family members vs 12% (4/33) of unaffected family members (P = .003). In DP subjects with no family history of IHH, 14% (8/56) had potentially pathogenic variants in IHH genes vs 5.6% (1 907/33 855) of controls (P = .01). Potentially pathogenic variants were found in multiple DP subjects for the genes IL17RD and TAC3.

CONCLUSIONS

These findings suggest that variants in IHH genes can contribute to the pathogenesis of self-limited DP. Thus, at least in some cases, self-limited DP shares an underlying pathophysiology with IHH.

Triallelic digenic mutation in the prokineticin 2 and GNRH receptor genes in two brothers with normosmic congenital hypogonadotropic hypogonadism

Purpose/aim of the study: To date, different genes have been identified as responsible for the presence of normosmic congenital hypogonadotropic hypogonadism (nCHH). Herein, we report the molecular findings regarding the analysis of PROK2, in two brothers with nCHH.

SUBJECTS AND METHODS

Two siblings with nCHH, in whom mutations in GNRHR, PROKR2 and FGFR1 had been investigated previously, as well as their family were studied. DNA was amplified by PCR and sequenced for the PROK2 gene. Controls were analyzed by restriction fragment-length polymorphism. The structure of PROK2 and its mutant protein were compared using a protein molecular model.

RESULTS

Both affected siblings exhibited a heterozygous p.R117W mutation in PROK2, while their mother was a heterozygous carrier and their father, an unaffected brother and their sister were homozygous wild type. Besides, both patients presented a homozygous p.E90K mutation in GNRHR that had been previously reported.

CONCLUSIONS

We found a novel mutation in PROK2 in two siblings in whom a mutation in the GNRHR gene had been previously reported.

Combined pituitary hormone deficiency: current and future status

Over the last two decades, the understanding of the mechanisms involved in pituitary ontogenesis has largely increased. Since the first description of POU1F1 human mutations responsible for a well-defined phenotype without extra-pituitary malformation, several other genetic defects of transcription factors have been reported with variable degrees of phenotype-genotype correlations. However, to date, despite the identification of an increased number of genetic causes of isolated or multiple pituitary deficiencies, the etiology of most (80-90 %) congenital cases of hypopituitarism remains unsolved. Identifying new etiologies is of importance as a post-natal diagnosis to better diagnose and treat the patients (delayed pituitary deficiencies, differential diagnosis of a pituitary mass on MRI, etc.), and as a prenatal diagnosis to decrease the risk of early death (undiagnosed corticotroph deficiency for instance). The aim of this review is to summarize the main etiologies and phenotypes of combined pituitary hormone deficiencies, associated or not with extra-pituitary anomalies, and to suggest how the identification of such etiologies could be improved in the near future.

Congenital hypogonadotropic hypogonadism with split hand/foot malformation: a clinical entity with a high frequency of FGFR1 mutations

PURPOSE

Congenital hypogonadotropic hypogonadism (CHH) and split hand/foot malformation (SHFM) are two rare genetic conditions. Here we report a clinical entity comprising the two.

METHODS

We identified patients with CHH and SHFM through international collaboration. Probands and available family members underwent phenotyping and screening for FGFR1 mutations. The impact of identified mutations was assessed by sequence- and structure-based predictions and/or functional assays.

RESULTS

We identified eight probands with CHH with (n = 3; Kallmann syndrome) or without anosmia (n = 5) and SHFM, seven of whom (88%) harbor FGFR1 mutations. Of these seven, one individual is homozygous for p.V429E and six individuals are heterozygous for p.G348R, p.G485R, p.Q594*, p.E670A, p.V688L, or p.L712P. All mutations were predicted by in silico analysis to cause loss of function. Probands with FGFR1 mutations have severe gonadotropin-releasing hormone deficiency (absent puberty and/or cryptorchidism and/or micropenis). SHFM in both hands and feet was observed only in the patient with the homozygous p.V429E mutation; V429 maps to the fibroblast growth factor receptor substrate 2α binding domain of FGFR1, and functional studies of the p.V429E mutation demonstrated that it decreased recruitment and phosphorylation of fibroblast growth factor receptor substrate 2α to FGFR1, thereby resulting in reduced mitogen-activated protein kinase signaling.

CONCLUSION

FGFR1 should be prioritized for genetic testing in patients with CHH and SHFM because the likelihood of a mutation increases from 10% in the general CHH population to 88% in these patients.

Reversal and relapse of hypogonadotropic hypogonadism: resilience and fragility of the reproductive neuroendocrine system

CONTEXT

A subset of patients diagnosed with idiopathic hypogonadotropic hypogonadism (IHH) later achieves activation of their hypothalamic-pituitary-gonadal axis with normalization of steroidogenesis and/or gametogenesis, a phenomenon termed reversal.

OBJECTIVE

The objective of this study was to determine the natural history of reversal and to identify associated phenotypes and genotypes.

DESIGN, SETTING, AND SUBJECTS

This was a retrospective review of clinical, biochemical, and genetic features of patients with IHH evaluated at an academic medical center.

MAIN OUTCOME MEASURES

History of spontaneous fertility, regular menses, testicular growth, or normalization of serum sex steroids, LH secretory profiles, brain imaging findings, and sequences of 14 genes associated with IHH were reviewed.

RESULTS

Of 308 patients with IHH, 44 underwent reversal. Time-to-event analysis estimated a lifetime incidence of reversal of 22%. There were no differences in the rates of cryptorchidism, micropenis, or partial pubertal development in patients with reversal vs IHH patients without reversal. Fifteen patients with reversal (30%) had Kallmann syndrome (IHH and anosmia); one had undetectable olfactory bulbs on a brain magnetic resonance imaging scan. Subjects with reversal were enriched for mutations affecting neurokinin B signaling compared with a cohort of IHH patients without reversal (10% vs 3%, P = .044), had comparable frequencies of mutations in FGFR1, PROKR2, and GNRHR, and had no mutations in KAL1. Five men did not sustain their reversal and again developed hypogonadotropism.

CONCLUSIONS

Reversal of IHH may be more widespread than previously appreciated and occurs across a broad range of genotypes and phenotypes. Enrichment for mutations that disrupt neurokinin B signaling in patients who reversed indicates that, despite the importance of this signaling pathway for normal pubertal timing, its function is dispensable later in life. The occurrence of reversal in a patient with no olfactory bulbs demonstrates that these structures are not essential for normal reproductive function. Patients with IHH require lifelong monitoring for reversal and, if reversal occurs, subsequent relapse also may occur.

Genetic rescue of Muenke syndrome model hearing loss reveals prolonged FGF-dependent plasticity in cochlear supporting cell fates

Muenke syndrome model mice (Fgfr3^P244R/+) have hearing loss associated with a supporting cell fate transformation of two Deiters' cells to two pillar cells. Mansour et al. find that the hearing loss is not rescued by reducing the FGFR3c ligand FGF8, but reducing FGF10 is sufficient to rescue cochlear form and function. The P244R mutation caused FGFR3b and FGFR3c to acquire responsiveness to FGF10. Fgf10 heterozygosity allows a gradual reversion of fate-switched cells toward the normal phenotype.

The stereotyped arrangement of cochlear sensory and supporting cells is critical for auditory function. Our previous studies showed that Muenke syndrome model mice (Fgfr3^P244R/+) have hearing loss associated with a supporting cell fate transformation of two Deiters' cells to two pillar cells. We investigated the developmental origins of this transformation and found that two prospective Deiters' cells switch to an outer pillar cell-like fate sequentially between embryonic day 17.5 (E17.5) and postnatal day 3 (P3). Unexpectedly, the Fgfr3^P244R/+ hearing loss and supporting cell fate transformation are not rescued by genetically reducing fibroblast growth factor 8 (FGF8), the FGF receptor 3c (FGFR3c) ligand required for pillar cell differentiation. Rather, reducing FGF10, which normally activates FGFR2b or FGFR1b, is sufficient for rescue of cochlear form and function. Accordingly, we found that the P244R mutation changes the specificity of FGFR3b and FGFR3c such that both acquire responsiveness to FGF10. Moreover, Fgf10 heterozygosity does not block the Fgfr3^P244R/+ supporting cell fate transformation but instead allows a gradual reversion of fate-switched cells toward the normal phenotype between P5 and at least P14. This study indicates that Deiters' and pillar cells can reversibly switch fates in an FGF-dependent manner over a prolonged period of time. This property might be exploited for the regulation of sensory cell regeneration from support cells.

Where genotype is not predictive of phenotype: towards an understanding of the molecular basis of reduced penetrance in human inherited disease

Some individuals with a particular disease-causing mutation or genotype fail to express most if not all features of the disease in question, a phenomenon that is known as 'reduced (or incomplete) penetrance'. Reduced penetrance is not uncommon; indeed, there are many known examples of 'disease-causing mutations' that fail to cause disease in at least a proportion of the individuals who carry them. Reduced penetrance may therefore explain not only why genetic diseases are occasionally transmitted through unaffected parents, but also why healthy individuals can harbour quite large numbers of potentially disadvantageous variants in their genomes without suffering any obvious ill effects. Reduced penetrance can be a function of the specific mutation(s) involved or of allele dosage. It may also result from differential allelic expression, copy number variation or the modulating influence of additional genetic variants in cis or in trans. The penetrance of some pathogenic genotypes is known to be age- and/or sex-dependent. Variable penetrance may also reflect the action of unlinked modifier genes, epigenetic changes or environmental factors. At least in some cases, complete penetrance appears to require the presence of one or more genetic variants at other loci. In this review, we summarize the evidence for reduced penetrance being a widespread phenomenon in human genetics and explore some of the molecular mechanisms that may help to explain this enigmatic characteristic of human inherited disease.

Mutations in FGF17, IL17RD, DUSP6, SPRY4, and FLRT3 are identified in individuals with congenital hypogonadotropic hypogonadism

Congenital hypogonadotropic hypogonadism (CHH) and its anosmia-associated form (Kallmann syndrome [KS]) are genetically heterogeneous. Among the >15 genes implicated in these conditions, mutations in FGF8 and FGFR1 account for ~12% of cases; notably, KAL1 and HS6ST1 are also involved in FGFR1 signaling and can be mutated in CHH. We therefore hypothesized that mutations in genes encoding a broader range of modulators of the FGFR1 pathway might contribute to the genetics of CHH as causal or modifier mutations. Thus, we aimed to (1) investigate whether CHH individuals harbor mutations in members of the so-called "FGF8 synexpression" group and (2) validate the ability of a bioinformatics algorithm on the basis of protein-protein interactome data (interactome-based affiliation scoring [IBAS]) to identify high-quality candidate genes. On the basis of sequence homology, expression, and structural and functional data, seven genes were selected and sequenced in 386 unrelated CHH individuals and 155 controls. Except for FGF18 and SPRY2, all other genes were found to be mutated in CHH individuals: FGF17 (n = 3 individuals), IL17RD (n = 8), DUSP6 (n = 5), SPRY4 (n = 14), and FLRT3 (n = 3). Independently, IBAS predicted FGF17 and IL17RD as the two top candidates in the entire proteome on the basis of a statistical test of their protein-protein interaction patterns to proteins known to be altered in CHH. Most of the FGF17 and IL17RD mutations altered protein function in vitro. IL17RD mutations were found only in KS individuals and were strongly linked to hearing loss (6/8 individuals). Mutations in genes encoding components of the FGF pathway are associated with complex modes of CHH inheritance and act primarily as contributors to an oligogenic genetic architecture underlying CHH.

Responsiveness to a physiological regimen of GnRH therapy and relation to genotype in women with isolated hypogonadotropic hypogonadism

CONTEXT

Isolated hypogonadotropic hypogonadism (IHH) is caused by defective GnRH secretion or action resulting in absent or incomplete pubertal development and infertility. Most women with IHH ovulate with physiological GnRH replacement, implicating GnRH deficiency as the etiology. However, a subset does not respond normally, suggesting the presence of defects at the pituitary or ovary.

OBJECTIVES

The objective of the study was to unmask pituitary or ovarian defects in IHH women using a physiological regimen of GnRH replacement, relating these responses to genes known to cause IHH.

DESIGN, SETTING, AND SUBJECTS

This study is a retrospective analysis of 37 IHH women treated with iv pulsatile GnRH (75 ng/kg per bolus).

MAIN OUTCOME MEASURES

Serum gonadotropin and sex steroid levels were measured, and 14 genes implicated in IHH were sequenced.

RESULTS

During their first cycle of GnRH replacement, normal cycles were recreated in 60% (22 of 37) of IHH women. Thirty percent of women (12 of 37) demonstrated an attenuated gonadotropin response, indicating pituitary resistance, and 10% (3 of 37) exhibited an exaggerated FSH response, consistent with ovarian resistance. Mutations in CHD7, FGFR1, KAL1, TAC3, and TACR3 were documented in IHH women with normal cycles, whereas mutations were identified in GNRHR, PROKR2, and FGFR1 in those with pituitary resistance. Women with ovarian resistance were mutation negative.

CONCLUSIONS

Although physiological replacement with GnRH recreates normal menstrual cycle dynamics in most IHH women, hypogonadotropic responses in the first week of treatment identify a subset of women with pituitary dysfunction, only some of whom have mutations in GNRHR. IHH women with hypergonadotropic responses to GnRH replacement, consistent with an additional ovarian defect, did not have mutations in genes known to cause IHH, similar to our findings in a subset of IHH men with evidence of an additional testicular defect.

Submicroscopic deletion involving the fibroblast growth factor receptor 1 gene in a patient with combined pituitary hormone deficiency

Combined pituitary hormone deficiency (CPHD), isolated hypogonadotropic hypogonadism (IHH), Kallmann syndrome (KS), and septo-optic dysplasia (SOD) are genetically related conditions caused by abnormal development of the anterior midline in the forebrain. Although mutations in the fibroblast growth factor receptor 1 (FGFR1) gene have been implicated in the development of IHH, KS, and SOD, the relevance of FGFR1 abnormalities to CPHD remains to be elucidated. Here, we report a Japanese female patient with CPHD and FGFR1 haploinsufficiency. The patient was identified through copy-number analyses and direct sequencing of FGFR1 performed for 69 patients with CPHD. The patient presented with a combined deficiency of GH, LH and FSH, and multiple neurological abnormalities. In addition, normal TSH values along with a low free T4 level indicated the presence of central hypothyroidism. Molecular analyses identified a heterozygous ~ 8.5 Mb deletion involving 56 genes and pseudogenes. None of these genes except FGFR1 have been associated with brain development. No FGFR1 abnormalities were identified in the remaining 68 patients, although two patients carried nucleotide substitutions (p.V102I and p.S107L) that were assessed as benign polymorphism by in vitro functional assays. These results indicate a possible role of FGFR1 in anterior pituitary function and the rarity of FGFR1 abnormalities in patients with CPHD.

PROK2/PROKR2 Signaling and Kallmann Syndrome

Kallmann syndrome (KS) is a developmental disease that associates hypogonadism and a deficiency of the sense of smell. The reproductive phenotype of KS results from the primary interruption of the olfactory, vomeronasal, and terminal nerve fibers in the frontonasal region, which in turn disrupts the embryonic migration of neuroendocrine gonadotropin-releasing hormone (GnRH) synthesizing cells from the nose to the brain. This is a highly heterogeneous genetic disease, and mutations in any of the nine genes identified so far have been found in approximately 30% of the KS patients. PROKR2 and PROK2, which encode the G protein-coupled prokineticin receptor-2 and its ligand prokineticin-2, respectively, are two of these genes. Homozygous knockout mice for the orthologous genes exhibit a phenotype reminiscent of the KS features, but biallelic mutations in PROKR2 or PROK2 (autosomal recessive mode of disease transmission) have been found only in a minority of the patients, whereas most patients carrying mutations in these genes are heterozygotes. The mutations, mainly missense mutations, have deleterious effects on PROKR2 signaling in transfected cells, ranging from defective cell surface-targeting of the receptor to defective coupling to G proteins or impaired receptor-ligand interaction, but the same mutations have also been found in apparently unaffected individuals, which suggests a digenic/oligogenic mode of inheritance of the disease in heterozygous patients. This non-Mendelian mode of inheritance has so far been confirmed only in a few patients. However, it may account for the unusually high proportion of KS sporadic cases compared to familial cases.