GnRH receptor and GPR54 inactivation in isolated gonadotropic deficiency

High Population Frequency of GNRHR p.Q106R in Malta: An Evaluation of Fertility and Hormone Profiles in Heterozygotes

Context

The gonadotropin-releasing hormone receptor variant GNRHR p.Q106R (rs104893836) in homozygosity, compound heterozygosity, or single heterozygosity is often reported as the causative variant in idiopathic hypogonadotropic hypogonadism (IHH) patients with GnRH deficiency. Genotyping of a Maltese newborn cord-blood collection yielded a minor allele frequency (MAF) 10 times higher (MAF = 0.029; n = 493) than that of the global population (MAF = 0.003).

Objective

To determine whether GNRHR p.Q106R in heterozygosity influences profiles of endogenous hormones belonging to the hypothalamic-pituitary axis and the onset of puberty and fertility in adult men (n = 739) and women (n = 239).

Design Setting and Participants

Analysis of questionnaire data relating to puberty and fertility, genotyping of the GNRHR p.Q106R variant, and hormone profiling of a highly phenotyped Maltese adult cohort from the Maltese Acute Myocardial Infarction Study.

Main Outcome and Results

Out of 978 adults, 43 GNRHR p.Q106R heterozygotes (26 men and 17 women) were identified. Hormone levels and fertility for all heterozygotes are within normal parameters except for TSH, which was lower in men 50 years or older.

Conclusion

Hormone data and baseline fertility characteristics of GNRHR p.Q106R heterozygotes are comparable to those of homozygous wild-type individuals who have no reproductive problems. The heterozygous genotype alone does not impair the levels of investigated gonadotropins and sex steroid hormones or affect fertility. GNRHR p.Q106R heterozygotes who exhibit IHH characteristics must have at least another variant, probably in a different IHH gene, that drives pathogenicity. We also conclude that GNRHR p.Q106R is likely a founder variant due to its overrepresentation and prevalence in the island population of Malta.

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.

Role of Kisspeptin on Hypothalamic-Pituitary-Gonadal Pathology and Its Effect on Reproduction

Kisspeptin is a neuropeptide that plays a significant role in human reproduction by its action on the hypothalamic-pituitary-gonadal (HPG) axis and functions through a G-protein-coupled receptor called G-protein-coupled receptor 54/kisspeptin 1 receptor (GPR54/KISS1R). It is encoded by the kisspeptin 1 (KISS1) gene that is mainly expressed in the hypothalamus. Kisspeptins are also recognized as vital aspects of maturation and proper function of the reproductive system in both males and females. It also plays its role in the onset of puberty, sexual patterns, desires, ovum development in women, sperm quality in men, feedback mechanisms, pregnancy, and lactation. Studies proved the pathological role of kisspeptin dysregulation in disorders like polycystic ovarian syndrome (PCOS) and infertility. Mutations in the KISS1 gene also contribute to precocious puberty or hypogonadotropic hypogonadism, depending upon the nature of mutations. Levels of kisspeptin also aid in the identification of a few pregnancy-related complications like preeclampsia, intrauterine growth restriction, and act as a marker of miscarriage. Due to the wide range of effects that kisspeptin has on the reproductive axis, investigations are being carried out to develop it as a diagnostic marker, treat diseases like hypogonadism and PCOS, and solve infertility issues.

Kisspeptin and GnRH interactions in the reproductive brain of teleosts

It is well known that gonadotropin-releasing hormone (Gnrh) has a key role in reproduction by regulating the synthesis and release of gonadotropins from the anterior pituitary gland of all vertebrates. About 25 years ago, another neuropeptide, kisspeptin (Kiss1) was discovered as a metastasis suppressor of melanoma cell lines and then found to be essential for mammalian reproduction as a stimulator of hypothalamic Gnrh and regulator of puberty onset. Soon after, a kisspeptin receptor (kissr) was found in the teleost brain. Nowadays, it is known that in most teleosts the kisspeptin system is composed of two ligands, kiss1 and kiss2, and two receptors, kiss2r and kiss3r. Even though both kisspeptin peptides, Kiss1 and Kiss2, have been demonstrated to stimulate gonadotropin synthesis and secretion in different fish species, their actions appear not to be mediated by Gnrh neurons as in mammalian models. In zebrafish and medaka, at least, hypophysiotropic Gnrh neurons do not express Kiss receptors. Furthermore, kisspeptinergic nerve terminals reach luteinizing hormone cells in some fish species, suggesting a direct pituitary action. Recent studies in zebrafish and medaka with targeted mutations of kiss and/or kissr genes reproduce relatively normally. In zebrafish, single gnrh mutants and additionally those having the triple gnrh3 plus 2 kiss mutations can reproduce reasonably well. In these fish, other neuropeptides known to affect gonadotropin secretion were up regulated, suggesting that they may be involved in compensatory responses to maintain reproductive processes. In this context, the present review explores and presents different possibilities of interactions between Kiss, Gnrh and other neuropeptides known to affect reproduction in teleost fish. Our intention is to stimulate a broad discussion on the relative roles of kisspeptin and Gnrh in the control of teleost reproduction.

Targeted mutation of secretogranin-2 disrupts sexual behavior and reproduction in zebrafish

The luteinizing hormone surge is essential for fertility as it triggers ovulation in females and sperm release in males. We previously reported that secretoneurin-a, a neuropeptide derived from the processing of secretogranin-2a (Scg2a), stimulates luteinizing hormone release, suggesting a role in reproduction. Here we provide evidence that mutation of the scg2a and scg2b genes using TALENs in zebrafish reduces sexual behavior, ovulation, oviposition, and fertility. Large-scale spawning within-line crossings (n = 82 to 101) were conducted. Wild-type (WT) males paired with WT females successfully spawned in 62% of the breeding trials. Spawning success was reduced to 37% (P = 0.006), 44% (P = 0.0169), and 6% (P < 0.0001) for scg2a ^-/- , scg2b ^-/- , and scg2a ^-/- ;scg2b ^-/- mutants, respectively. Comprehensive video analysis indicates that scg2a ^-/- ;scg2b ^-/- mutation reduces all male courtship behaviors. Spawning success was 47% in saline-injected WT controls compared to 11% in saline-injected scg2a ^-/- ;scg2b ^-/- double mutants. For these mutants, spawning success increased 3-fold following a single intraperitoneal (i.p.) injection of synthetic secretoneurin-a (P = 0.0403) and increased 3.5-fold with injection of human chorionic gonadotropin (hCG). Embryonic survival at 24 h remained on average lower in scg2a ^-/- ;scg2b ^-/- fish compared to WT injected with secretoneurin-a (P < 0.001). Significant reductions in the expression of gonadotropin-releasing hormone 3 in the hypothalamus, and luteinizing hormone beta and glycoprotein alpha subunits in the pituitary provide evidence for disrupted hypothalamo-pituitary function in scg2a and scg2b mutant fish. Our results indicate that secretogranin-2 is required for optimal reproductive function and support the hypothesis that secretoneurin is a reproductive hormone.

Genetics of congenital hypogonadotropic hypogonadism: peculiarities and phenotype of an oligogenic disease

A genetic basis of congenital isolated hypogonadotropic hypogonadism (CHH) can be defined in almost 50% of cases, albeit not necessarily the complete genetic basis. Next-generation sequencing (NGS) techniques have led to the discovery of a great number of loci, each of which has illuminated our understanding of human gonadotropin-releasing hormone (GnRH) neurons, either in respect of their embryonic development or their neuroendocrine regulation as the "pilot light" of human reproduction. However, because each new gene linked to CHH only seems to underpin another small percentage of total patient cases, we are still far from achieving a comprehensive understanding of the genetic basis of CHH. Patients have generally not benefited from advances in genetics in respect of novel therapies. In most cases, even genetic counselling is limited by issues of apparent variability in expressivity and penetrance that are likely underpinned by oligogenicity in respect of known and unknown genes. Robust genotype-phenotype relationships can generally only be established for individuals who are homozygous, hemizygous or compound heterozygotes for the same gene of variant alleles that are predicted to be deleterious. While certain genes are purely associated with normosmic CHH (nCHH) some purely with the anosmic form (Kallmann syndrome-KS), other genes can be associated with both nCHH and KS-sometimes even within the same kindred. Even though the anticipated genetic overlap between CHH and constitutional delay in growth and puberty (CDGP) has not materialised, previously unanticipated genetic relationships have emerged, comprising conditions of combined (or multiple) pituitary hormone deficiency (CPHD), hypothalamic amenorrhea (HA) and CHARGE syndrome. In this review, we report the current evidence in relation to phenotype and genetic peculiarities regarding 60 genes whose loss-of-function variants can disrupt the central regulation of reproduction at many levels: impairing GnRH neurons migration, differentiation or activation; disrupting neuroendocrine control of GnRH secretion; preventing GnRH neuron migration or function and/or gonadotropin secretion and action.

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.

Facing the Challenges of Neuropeptide Gene Knockouts: Why Do They Not Inhibit Reproduction in Adult Teleost Fish?

Genetic manipulation of teleost endocrine systems started with transgenic overexpression of pituitary growth hormone. Such strategies enhance growth and reduce fertility, but the fish still breed. Genome editing using transcription activator-like effector nuclease in zebrafish and medaka has established the role of follicle stimulating hormone for gonadal development and luteinizing hormone for ovulation. Attempts to genetically manipulate the hypophysiotropic neuropeptidergic systems have been less successful. Overexpression of a gonadotropin-releasing hormone (gnrh) antisense in common carp delays puberty but does not block reproduction. Knockout of Gnrh in zebrafish does not impact either sex, while in medaka this blocks ovulation in females without affecting males. Spawning success is not reduced by knockout of the kisspeptins and receptors, agouti-related protein, agouti signaling peptide or spexin. Hypotheses for the lack of effect of these genome edits are presented. Over evolutionary time, teleosts have lost the median eminence typical of mammals. There is consequently direct innervation of gonadotrophs, with the possibility of independent regulation by >20 neurohormones. Removal of a few may have minimal impact. Neuropeptide knockout could leave co-expressed stimulators of gonadotropins functionally intact. Genetic compensation in response to loss of protein function may maintain sufficient reproduction. The species differences in hypothalamo-hypophysial anatomy could be an example of compensation over the evolutionary timescale as teleosts diversified and adapted to new ecological niches. The key neuropeptidergic systems controlling teleost reproduction remain to be uncovered. Classical neurotransmitters are also regulators of luteinizing hormone release, but have yet to be targeted by genome editing. Their essentiality for reproduction should also be explored.

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.

A novel mutation in SOX2 causes hypogonadotropic hypogonadism with mild ocular malformation

BACKGROUND

Heterozygous SOX2 mutations have been reported to cause isolated hypogonadotropic hypogonadism (HH) in addition to ocular and brain abnormalities.

OBJECTIVE

We report a novel missense SOX2 (Y110C) mutation in an HH patient with mild ocular malformation.

PATIENTS

The 20-year-old male was referred because of typical signs of complete hypogonadism, with small intrascrotal testes (2 ml), no pubic hair (P1), and a micropenis. Hormone assays revealed very low plasma testosterone levels and very low levels of plasma gonadotropin. He was found to have retinal detachment in his right eye and surgery was performed at the age of 14 years.

RESULTS

Using a next-generation sequencing strategy, we identified a novel heterozygous SOX2 mutation, c.329A>G (p.Y110C). Y110C SOX2 had reduced transactivation and no dominant negative effect. Subcellular localization revealed no significant difference between wild-type and mutant SOX2. EMSA experiments showed that the Y110C SOX2 abrogated DNA-binding ability.

CONCLUSION

The Y110C mutation affects a critical residue in the SOX2 protein. This study extends our understanding of the phenotypic features, molecular mechanism, and developmental course associated with mutations in SOX2. When multiple genes need to be analyzed for mutations simultaneously, targeted sequence analysis of interesting genomic regions is an attractive approach.

Molecular regulation of hypothalamus-pituitary-gonads axis in males

The hypothalamic-pituitary-gonadal axis (HPG) plays vital roles in reproduction and steroid hormone production in both sexes. The focus of this review is upon gene structures, receptor structures and the signaling pathways of gonadotropin-releasing hormone (GnRH), luteinizing hormone (LH) and follicle-stimulating hormone (FSH). The hormones' functions in reproduction as well as consequences resulting from mutations are also summarized. Specific characteristics of hormones such as the pulsatile secretions of GnRH are also covered. The different regulators of the HPG axis are introduced including kisspeptin, activin, inhibin, follistatin, androgens and estrogen. This review includes not only their basic information, but also their unique function in the HPG axis. Here we view the HPG axis as a whole, so relations between ligands and receptors are well described crossing different levels of the HPG axis. Hormone interactions and transformations are also considered. The major information of this article is depicted in three figures summarizing the current discoveries on the HPG axis. This article systematically introduces the basic knowledge of the HPG axis and provides information of the current advances relating to reproductive hormones.

Tachykinin: recent developments and novel roles in health and disease

Over 80 years has passed since the discovery of substance P (SP), and a variety of peptides of the tachykinin (TK) family have been found and investigated. SP, neurokinin A (NKA), and neurokinin B (NKB) are representative peptides in mammalian species. SP and NKA are major excitatory neurotransmitters in the peripheral nervous system, while NKB is primarily involved in the central nervous system (CNS). Moreover, TK peptides play roles not only as neurotransmitters but also as local factors and are involved in almost all aspects of the regulation of physiological functions and pathophysiological processes. The role of SP as a mediator of pain processing and inflammation in peripheral tissues in coordination with transient receptor potential channels is well established, while novel aspects of TKs in relation to hematopoiesis, venous thromboembolism, tendinopathy, and taste perception have been clarified. In the CNS, the NKB signaling system in the hypothalamus has been shown to play a crucial role in the regulation of gonadotropin hormone secretion and the onset of puberty, and molecular biological studies have elucidated novel prophylaxic activities of TKs against neurogenic movement disorders based on their molecular structure. This review provides an overview of the novel aspects of TKs reported around the world in the last 5 years, with particular focus on nociception, inflammation, hemopoiesis, gonadotropin secretion, and CNS diseases.

Kisspeptin: a new neuronal target of primer pheromones in the control of reproductive function in mammals

Pheromones are known to trigger either short-term behavioral responses, usually referred to as "releaser effects", or more long-term physiological changes, known as "primer effects", which especially affect reproductive function at the level of the gonadotrope axis. The precise mechanisms through which pheromones interact with the gonadotrope axis in the hypothalamus is not fully known. We propose that the neuropeptide Kisspeptin, could be a specific target of primer pheromones, allowing these pheromones to modulate the gonadotrope axis and GnRH activity. This emerging hypothesis is discussed in the context of puberty acceleration in female mice and the male effect in female ungulates (sheep or goat). These examples have been chosen to illustrate the diversity of the reproductive contexts in mammals and potential mechanisms affected by primer effects at the level of the gonadotrope axis.

KISS1 expression in human female adipose tissue

OBJECTIVE

The current focus of kisspeptin research is an exploration of its key role in the hypothalamic control of human and animal fertility. Notwithstanding the importance of these studies, strong evidence exists that the gene encoding human kisspeptin, KISS1, is present in several peripheral sites, including the placenta. We also provided evidence that kiss1 is also expressed and regulated in rodent adipose tissue. This study describes a pilot investigation into the possibility that human female adipose tissue might also express the KISS1 gene.

METHODS

Samples of fat were taken from women undergoing open abdominal surgery, for example, during caesarian section. Two small samples of fat were obtained, one from subcutaneous tissue (n = 35) and one from the omentum (n = 32). RNA was isolated from all fat samples and KISS1 mRNA was detected by realtime RT-PCR.

RESULTS

KISS1 gene expression was detected at varying levels in all samples of fat tissue but levels were significantly higher in subcutaneous fat. There was no significant correlation between KISS1 gene expression and body mass index (BMI) in subcutaneous fat (P = 0.43), but there was a significant positive correlation (P = 0.01) between KISS1 mRNA levels and BMI in omental adipose tissue.

CONCLUSION

We have shown for the first time that human female adipose tissue may be a source of kisspeptins. Further studies are required to establish whether kisspeptins of adipose tissue origin might be correlated with some aspects of infertility.

G protein-coupled receptors: mutations and endocrine diseases

Over the past 20 years, naturally occurring mutations that affect G protein-coupled receptors (GPCRs) have been identified, mainly in patients with endocrine diseases. The study of loss-of-function or gain-of-function mutations has contributed to our understanding of the pathophysiology of several diseases with classic hypophenotypes or hyperphenotypes of the target endocrine organs, respectively. Simultaneously, study of the mutant receptors ex vivo was instrumental in delineating the relationships between the structure and function of these important physiological and pharmacological molecules. Now that access to the crystallographic structure of a few GPCRs is available, the mechanics of these receptors can be studied at the atomic level. Progress in the fields of cell biology, molecular pharmacology and proteomics has also widened our view of GPCR functions. Initially considered simply as guanine nucleotide exchange factors capable of activating G protein-dependent regulatory cascades, GPCRs are now known to display several additional characteristics, each susceptible to alterations by disease-causing mutations. These characteristics include functionally important basal activity of the receptor; differential activation of various G proteins; differential activation of G protein-dependent and independent effects (biased agonism); interaction with proteins that modify receptor function; dimerization-dependent effects; and interaction with allosteric modulators. This Review attempts to illustrate how natural mutations of GPCR could contribute to our understanding of these novel facets of GPCR biology.

Molecular causes of hypogonadotropic hypogonadism

PURPOSE OF REVIEW

What controls puberty remains largely unknown and current gene mutations account for only about one-third of the apparently genetic cases of idiopathic hypogonadotropic hypogonadism. Lately important developments have occurred in this field.

RECENT FINDINGS

Substantial variation in clinical expression, from complete anosmia and hypogonadotropic hypogonadism to delayed puberty and normosmia, of the same Kallmann syndrome gene defects including in newer ones (FGF8 and CHD7) continues to be repeatedly observed. Digenic or oligogenic inheritance becomes another feature of Kallmann syndrome. Recent reports of mutations in TAC3 or TACR3 [encoding neurokinin B (NKB) and its receptor, NK3R, respectively] provided compelling evidence for the involvement of NKB signaling in puberty. This energized the field to understand the exact mechanism through which NKB signaling exerts its effects. With the important findings from these recent studies in association with the substantial data from kisspeptin studies in the last 6 years a sketch of GnRH pulse generator has emerged in which NKB signaling appears to play a key role.

SUMMARY

Autozygosity mapping may continue helping identify the other genes including those upstream to the GnRH pulse generator in this complex and elusive developmental process.

The recent genetics of hypogonadotrophic hypogonadism - novel insights and new questions

The complex organization and regulation of the human hypothalamic-pituitary-gonadal axis render it susceptible to dysfunction in the face of a variety of genetic insults, leading to different degrees of hypogonadotrophic hypogonadism (HH). Although the genetic basis of some HH was recognized more than 60 years ago the first specific pathogenic defect, in the KAL1 gene, was only identified within the last 20 years. In the past decade, the rate of genetic discovery has dramatically accelerated, with defects in more than 10 genes now associated with HH. Several themes have emerged as the genetic basis of HH has gradually been uncovered, including the association of some genes such as FGFR1, FGF8, PROK2 and PROKR2, both with HH in association with hyposmia/anosmia (Kallmann syndrome) and with normosmic HH, thus blurring the clinical distinction between ontogenic and purely functional defects in the axis. Many examples of digenic inheritance of HH have also been reported, sometimes producing variable reproductive and accessory phenotypes within a family with non-Mendelian inheritance patterns. In strictly normosmic HH, human genetics has made a particularly dramatic impact in the past 6 years through homozygosity mapping in consanguineous families, first through identification of a key role for kisspeptin in triggering GnRH release, and very recently through demonstration of a critical role for neurokinin B in normal sexual maturation. This review summarises current understanding of the genetic architecture of HH, as well as its diagnostic and mechanistic implications.

Disruption of the single copy gonadotropin-releasing hormone receptor in mice by gene trap: severe reduction of reproductive organs and functions in developing and adult mice

Mutations in the GnRH receptor gene (GNRHR) can result in hypogonadotropic hypogonadism in humans. Unlike most mammals, mice lack a second form of GnRH (GnRH2) and a type 2 GnRH receptor. To determine whether the GnRH receptor is critical at all stages of reproduction and whether this receptor has additional physiological functions in developing and adult mice, we have generated mice from an embryonic stem cell line containing a retroviral vector with multiple stop codons inserted into intron 1 of the Gnrhr gene. This gene trap insertion resulted in the disruption of exon 2 and exon 3 of the Gnrhr gene. The insertion also contained a lacZ gene that was used as a reporter for GnRH receptor expression in these mice. This model has a similar phenotype to the clinical syndrome of hypogonadotropic hypogonadism. Null Gnrhr mice had small sexual organs, low levels of FSH, LH, and steroid hormones, failure of sexual maturation, infertility, and inability to respond to exogenous GnRH. However, the defective GnRH receptor did not prevent morula/blastocyst development, implantation, masculinization of fetal male mice, or maintenance of early pregnancy. The phenotype of this null Gnrhr mouse was more severe than models in the literature, including the N-ethyl-N-nitrosourea-induced Gnrhr mutant, the kisspeptin (Kiss1) knockout, and the kisspeptin receptor (Gpr54) knockout. In terms of gonadal morphology, adult gene trap-Gnrhr null mice demonstrate a complete cessation of reproduction and serve as an important model for understanding GnRH/GnRHR physiology.

The genetic and molecular basis of idiopathic hypogonadotropic hypogonadism

Idiopathic hypogonadotropic hypogonadism (IHH) has an incidence of 1-10 cases per 100,000 births. About 60% of patients with IHH present with associated anosmia, also known as Kallmann syndrome, characterized by total or partial loss of olfaction. Many of the gene mutations associated with Kallmann syndrome have been mapped to KAL1 or FGFR1. However, together, these mutations account for only about 15% of Kallmann syndrome cases. More recently, mutations in PROK2 and PROKR2 have been linked to the syndrome and may account for an additional 5-10% of cases. The remaining 40% of patients with IHH have a normal sense of smell. Prior to 2003, the only gene linked to normosmic IHH was the gonadotropin-releasing hormone receptor gene. However, mutations in this receptor are believed to account for only 10% of cases. Subsequently, mutations in KISS1R, TAC3 and TACR3 were identified as causes of normosmic IHH. Certain genes, including PROK2 and FGFR1, are associated with both anosmic and normosmic IHH. Despite recent advances in the field, the genetic causes of the majority of cases of IHH remain unknown. This Review discusses genes associated with hypogonadotropic disorders and the molecular mechanisms by which mutations in these genes may result in IHH.

KiSS-1 mRNA in adipose tissue is regulated by sex hormones and food intake

Hypothalamic KiSS-1 gene expression is critical for the maintenance of reproductive function, and levels are attenuated by sex hormones and by food restriction, providing a link between fat mass and fertility. We hypothesized that adipose tissue (FAT) would express KiSS-1. KiSS-1 mRNA was quantified in FAT, hypothalamus (HYP) and pituitary gland (PIT) using realtime RT-PCR. FAT KiSS-1 expression was sensitive to sex steroids and to nutritional status. Gonadectomized rats given estradiol (E; females) or testosterone (T; males) revealed striking increases in KiSS-1 mRNA in FAT (E: 8-fold, p<0.01; T: 5-fold, p<0.01). In contrast, HYP KiSS-1 expression was reduced by E/T, whereas PIT expression was reduced by gonadectomy only in females, reversed by E. Food restriction (18 h) increased FAT KiSS-1 mRNA in both sexes (2.5-4.0-fold, p<0.01), but decreased levels in male PIT and female HYP. Conversely, FAT expression was reduced in rats fed a high fat diet (HFD), as well as in obese Zucker rats, whereas PIT expression was increased in Zucker rats (p<0.05) but not by HFD. In contrast HYP KiSS-1 mRNA was elevated by HFD. Experiments in which the arcuate nucleus was damaged by an excitotoxic lesion revealed that hypothalamic KiSS-1 mRNA was significantly reduced, whereas FAT levels were unaffected, suggesting that regulation of KiSS-1 in FAT is independent of the hypothalamus. In conclusion, KiSS-1 expression is differentially regulated by sex hormones, food intake and obesity in FAT, HYP and PIT. Kisspeptins of adipose tissue origin may act as adipokines or as local regulators of adipocyte function.