Kallmann syndrome: mutations in the genes encoding prokineticin-2 and prokineticin receptor-2

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

CONTEXT

FGFR1 mutations have been identified in about 10% of patients with Kallmann syndrome. Recently cases of idiopathic hypogonadotropic hypogonadism (IHH) with a normal sense of smell (nIHH) have been reported.

AIMS

The objective of the study was to define the frequency of FGFR1 mutations in a large cohort of nIHH, delineate the spectrum of reproductive phenotypes, assess functionality of the FGFR1 mutant alleles in vitro, and investigate genotype-phenotype relationships.

DESIGN

FGFR1 sequencing of 134 well-characterized nIHH patients (112 men and 22 women) and 270 healthy controls was performed. The impact of the identified mutations on FGFR1 function was assessed using structural prediction and in vitro studies.

RESULTS

Nine nIHH subjects (five males and four females; 7%) harbor a heterozygous mutation in FGFR1 and exhibit a wide spectrum of pubertal development, ranging from absent puberty to reversal of IHH in both sexes. All mutations impair receptor function. The Y99C, Y228D, and I239T mutants impair the tertiary folding, resulting in incomplete glycosylation and reduced cell surface expression. The R250Q mutant reduces receptor affinity for FGF. The K618N, A671P, and Q680X mutants impair tyrosine kinase activity. However, the degree of functional impairment of the mutant receptors did not always correlate with the reproductive phenotype, and variable expressivity of the disease was noted within family members carrying the same FGFR1 mutation. These discrepancies were partially explained by additional mutations in known IHH loci.

CONCLUSIONS

Loss-of-function mutations in FGFR1 underlie 7% of nIHH with different degrees of impairment in vitro. These mutations act in concert with other gene defects in several cases, consistent with oligogenicity.

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.

GNRH1 mutations in patients with idiopathic hypogonadotropic hypogonadism

Idiopathic hypogonadotropic hypogonadism (IHH) is a condition characterized by failure to undergo puberty in the setting of low sex steroids and low gonadotropins. IHH is due to abnormal secretion or action of the master reproductive hormone gonadotropin-releasing hormone (GnRH). Several genes have been found to be mutated in patients with IHH, yet to date no mutations have been identified in the most obvious candidate gene, GNRH1 itself, which encodes the preprohormone that is ultimately processed to produce GnRH. We screened DNA from 310 patients with normosmic IHH (nIHH) and 192 healthy control subjects for sequence changes in GNRH1. In 1 patient with severe congenital nIHH (with micropenis, bilateral cryptorchidism, and absent puberty), a homozygous frameshift mutation that is predicted to disrupt the 3 C-terminal amino acids of the GnRH decapeptide and to produce a premature stop codon was identified. Heterozygous variants not seen in controls were identified in 4 patients with nIHH: 1 nonsynonymous missense mutation in the eighth amino acid of the GnRH decapeptide, 1 nonsense mutation that causes premature termination within the GnRH-associated peptide (GAP), which lies C-terminal to the GnRH decapeptide within the GnRH precursor, and 2 sequence variants that cause nonsynonymous amino-acid substitutions in the signal peptide and in GnRH-associated peptide. Our results establish mutations in GNRH1 as a genetic cause of nIHH.

Isolated familial hypogonadotropic hypogonadism and a GNRH1 mutation

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

A 785kb deletion of 3p14.1p13, including the FOXP1 gene, associated with speech delay, contractures, hypertonia and blepharophimosis

We report a child with a 785kb deletion of the 3p14.1p13 region including the genes FOXP1, EIF4E3, PROK2, GPR27 resulting in speech delay, contractures, hypertonia and blepharophimosis. FOXP1 and FOXP2 are transcription factors containing a polyglutamine tract and a forkhead DNA binding domain. They both play a role in the developing human foregut and brain [W. Shu, M.M. Lu, Y. Zhang, P. Tucker, D. Zhou, E.E. Morrisey, Foxp2 and Foxp1 cooperatively regulate lung and esophagus development, Development 134 (2007) 1991-2000, E. Spiteri, G. Konopka, G. Coppola, J. Bomar, M. Oldham, J. Ou, et al. Identification of the transcriptional targets of FOXP2, a gene linked to speech and language, in developing human brain, Am. J. Hum. Genet. 81 (2007) 1144-1157, S. Tamura, Y. Morikawa, H. Iwanishi, T. Hisaoka, E. Senba. Expression pattern of the winged-helix/forkhead transcription factor Foxp1 in the developing central nervous system, Gene Expr. Patterns. 3 (2003) 193-197.]. Mutations in FOXP2 are known to cause severe speech and language abnormalities [C.S.L. Lai, S.E. Fisher, J.A. Hurst, F. Vargha-Khadem, A.P. Monaco, A forkhead-domain gene is mutated in a severe speech and language disorder, Nature 413 (2001) 519-523.] in humans and animals. It has been suggested that overlap of FOXP1 and FOXP2 expression in the songbird and human brain may indicate that mutations in FOXP1 would also result in speech and language abnormalities. The roles of EIF4E3, PROK2 and GPR27 are also evaluated.

[Congenital hypogonadotropic hypogonadism]

Congenital hypogonadotropic hypogonadism is defined by reduced steroid hormone synthesis and secretion due to low LH and FSH secretion. It is a rare disease with an unknown prevalence (about 1/5000). It results from a fetal defect in GnRH neuron migration, a defect of pituitary development or from a functional defect of the hypothalamopituitary axis between GnRH neurons and gonadotropic cells. The diagnosis should be considered at birth in males with micropenis, during adolescence in case of delayed puberty or absent puberty, and during adulthood in case of infertility. It may be restricted to the gonadotropic axis, combined with other endocrine system defects or be part of a complex syndrome. Several gene defects have now been described. Molecular studies should be performed to confirm the diagnosis and to help provide appropriate genetic counseling. Treatment to induce puberty should be provided at adolescence, followed by hormonal substitution treatment during adulthood. Specific infertility treatment may also be proposed but patients with the dominant form of gonadotropic deficiency should be informed of the risk of transmission.

What controls the timing of puberty? An update on progress from genetic investigation

PURPOSE OF REVIEW

Puberty is an important developmental stage during which reproductive capacity is attained. Genetic and environmental factors both influence the timing of puberty, which varies greatly among individuals. However, although genetic variation is known to influence the normal spectrum of pubertal timing, the specific genes involved remain unknown.

RECENT FINDINGS

Recent genetic analyses have identified a number of genes responsible for rare disorders of pubertal timing such as hypogonadotropic hypogonadism and Kallmann syndrome. However, although the genetic basis of population variation in the timing of puberty is an active area of investigation, no genetic loci have been reproducibly associated with pubertal timing thus far.

SUMMARY

This review provides an update of the genes implicated in disorders of puberty, discusses genes and pathways that may be involved in the timing of normal puberty, and suggests additional avenues of investigation to identify genetic regulators of puberty in the general population.

PROKR2 missense mutations associated with Kallmann syndrome impair receptor signalling activity

Kallmann syndrome (KS) combines hypogonadism due to gonadotropin-releasing hormone deficiency, and anosmia or hyposmia, related to defective olfactory bulb morphogenesis. In a large series of KS patients, ten different missense mutations (p.R85C, p.R85H, p.R164Q, p.L173R, p.W178S, p.Q210R, p.R268C, p.P290S, p.M323I, p.V331M) have been identified in the gene encoding the G protein-coupled receptor prokineticin receptor-2 (PROKR2), most often in the heterozygous state. Many of these mutations were, however, also found in clinically unaffected individuals, thus raising the question of their actual implication in the KS phenotype. We reproduced each of the ten mutations in a recombinant murine Prokr2, and tested their effects on the signalling activity in transfected HEK-293 cells, by measuring intracellular calcium release upon ligand-activation of the receptor. We found that all mutated receptors except one (M323I) had decreased signalling activities. These could be explained by different defective mechanisms. Three mutations (L173R, W178S, P290S) impaired cell surface-targeting of the receptor. One mutation (Q210R) abolished ligand-binding. Finally, five mutations (R85C, R85H, R164Q, R268C, V331M) presumably impaired G protein-coupling of the receptor. In addition, when wild-type and mutant receptors were coexpressed in HEK-293 cells, none of the mutant receptors that were retained within the cells did affect cell surface-targeting of the wild-type receptor, and none of the mutant receptors properly addressed at the plasma membrane did affect wild-type receptor signalling activity. This argues against a dominant negative effect of the mutations in vivo.

Reproductive functions of kisspeptin and Gpr54 across the life cycle of mice and men

The reproductive phenotypes of nearly two dozen patients with mutations in GPR54 have been reported, as have the phenotypes of four mouse lines mutant for Gpr54 and two lines mutant for Kiss1. These phenotypes demonstrate that kisspeptin/Gpr54 function is required at all phases of the life cycle when the secretion of gonadotropin-releasing hormone (GnRH) is robust. Furthermore, there is phenotypic variability ranging from severe hypogonadism to partial sexual development. Collectively, these findings suggest that kisspeptin and Gpr54 serve as an essential conduit for relaying developmental information to the GnRH neuron.

Association of the timing of puberty with a chromosome 2 locus

CONTEXT

Twin studies indicate that the timing of pubertal onset is under strong genetic control. However, genes controlling pubertal timing in the general population have not yet been identified.

OBJECTIVE

To facilitate the identification of genes influencing the timing of pubertal growth and maturation, we conducted linkage mapping of constitutional delay of growth and puberty (CDGP), an extreme variant of normal pubertal timing, in extended families.

PARTICIPANTS AND METHODS

Fifty-two families multiply affected with CDGP were genotyped with 383 multiallelic markers. CDGP was defined based on growth charts (the age at onset of growth spurt, peak height velocity, or attaining adult height taking place at least 1.5 sd later than average). Chromosomal regions cosegregating with CDGP were identified with parametric affected-only linkage analysis using CDGP as a dichotomized trait.

RESULTS

The genome-wide scan detected linkage of CDGP to a region on chromosome 2p13-2q13. The two-point heterogeneity LOD (HLOD) score was 1.62 (alpha = 0.27), and the corresponding multipoint HLOD was 2.54 (alpha = 0.31). Fine-mapping the region at 1 cM resolution increased the multipoint HLOD score to 4.44 (alpha = 0.41). The linkage became weaker if family members diagnosed with CDGP without growth data were also included in the analyses.

CONCLUSIONS

The pericentromeric region of chromosome 2 harbors a gene predisposing to pubertal delay in multiply affected pedigrees. Our data suggest that this locus may be a component of the internal clock controlling the timing of the onset of puberty.

CHD7 mutations in patients initially diagnosed with Kallmann syndrome--the clinical overlap with CHARGE syndrome

Kallmann syndrome (KS) is the combination of hypogonadotropic hypogonadism and anosmia or hyposmia, two features that are also frequently present in CHARGE syndrome. CHARGE syndrome is caused by mutations in the CHD7 gene. We performed analysis of CHD7 in 36 patients with KS and 20 patients with normosmic idiopathic hypogonadotropic hypogonadism (nIHH) in whom mutations in KAL1, FGFR1, PROK2 and PROKR2 genes were excluded. Three of 56 KS/nIHH patients had de novo mutations in CHD7. In retrospect, these three CHD7-positive patients showed additional features that are seen in CHARGE syndrome. CHD7 mutations can be present in KS patients who have additional features that are part of the CHARGE syndrome phenotype. We did not find mutations in patients with isolated KS. These findings imply that patients diagnosed with hypogonadotropic hypogonadism and anosmia should be screened for clinical features consistent with CHARGE syndrome. If such features are present, particularly deafness, dysmorphic ears and/or hypoplasia or aplasia of the semicircular canals, CHD7 sequencing is recommended.

Kallmann syndrome

The Kallmann syndrome (KS) combines hypogonadotropic hypogonadism (HH) with anosmia. This is a clinically and genetically heterogeneous disease. KAL1, encoding the extracellular glycoprotein anosmin-1, is responsible for the X chromosome-linked recessive form of the disease. Mutations in FGFR1 or FGF8, encoding fibroblast growth factor receptor-1 and fibroblast growth factor-8, respectively, underlie an autosomal dominant form with incomplete penetrance. Finally, mutations in PROKR2 and PROK2, encoding prokineticin receptor-2 and prokineticin-2, have been found in heterozygous, homozygous, and compound heterozygous states. These two genes are likely to be involved both in monogenic recessive and digenic/oligogenic KS transmission modes. Notably, mutations in any of the above-mentioned KS genes have been found in less than 30% of the KS patients, which indicates that other genes involved in the disease remain to be discovered.

Association studies of common variants in 10 hypogonadotropic hypogonadism genes with age at menarche

CONTEXT

Although the timing of puberty is a highly heritable trait, little is known about the genes that regulate pubertal timing in the general population. Several genes have been identified that, when mutated, cause disorders of delayed or absent puberty such as hypogonadotropic hypogonadism (HH).

OBJECTIVE

Because severe variants in HH-related genes cause a severe puberty phenotype, we hypothesized that common subtle variation in these genes could contribute to the population variation in pubertal timing.

DESIGN

We assessed common genetic variation in 10 HH-related genes in 1801 women from the Hawaii and Los Angeles Multiethnic Cohort with either early (age<11 yr) or late (age>14 yr) menarche and in other replication samples. In addition to these common variants, we also studied the most frequently reported HH mutations to assess their role in the population variation in pubertal timing. SETTING AND PATIENTS/OTHER PARTICIPANTS: Within the general community, 1801 women from the Hawaii and Los Angeles Multiethnic Cohort participated.

MAIN OUTCOME MEASURES

We assessed the association of genetic variation with age at menarche.

RESULTS

We found no significant association between any of the variants tested and age at menarche, although we cannot rule out modest effects of these variants or of other variants at long distances from the coding region. In several self-reported racial/ethnic groups represented in our study, we observed an association between estimated genetic ancestry and age at menarche.

CONCLUSIONS

Our results suggest that common variants near 10 HH-related loci do not play a substantial role in the regulation of age at menarche in the general population.

Loss-of-function mutations in the genes encoding prokineticin-2 or prokineticin receptor-2 cause autosomal recessive Kallmann syndrome

CONTEXT

Physiological activation of the prokineticin pathway has a critical role in olfactory bulb morphogenesis and GnRH secretion in mice.

OBJECTIVE

To investigate PROK2 and PROKR2 mutations in patients with hypogonadotropic hypogonadism (HH) associated or not with olfactory abnormalities.

DESIGN

We studied 107 Brazilian patients with HH (63 with Kallmann syndrome and 44 with normosmic HH) and 100 control individuals. The coding regions of PROK2 and PROKR2 were amplified by PCR followed by direct automatic sequencing.

RESULTS

In PROK2, two known frameshift mutations were identified. Two brothers with Kallmann syndrome harbored the homozygous p.G100fsX121 mutation, whereas one male with normosmic HH harbored the heterozygous p.I55fsX56 mutation. In PROKR2, four distinct mutations (p.R80C, p.Y140X, p.L173R, and p.R268C) were identified in five patients with Kallmann syndrome and in one patient with normosmic HH. These mutations were not found in the control group. The p.R80C, p.L173R, and p.R268C missense mutations were identified in the heterozygous state in the HH patients and in their asymptomatic first-degree relatives. In addition, no mutations of FGFR1, KAL1, GnRHR, KiSS-1, or GPR54 were identified in these patients. Notably, the new nonsense mutation (p.Y140X) was identified in the homozygous state in an anosmic boy with micropenis, bilateral cryptorchidism, and high-arched palate. His asymptomatic parents were heterozygous for this severe defect.

CONCLUSION

We expanded the repertoire of PROK2 and PROKR2 mutations in patients with HH. In addition, we show that PROKR2 haploinsufficiency is not sufficient to cause Kallmann syndrome or normosmic HH, whereas homozygous loss-of-function mutations either in PROKR2 or PROK2 are sufficient to cause disease phenotype, in accordance with the Prokr2 and Prok2 knockout mouse models.

Mutations in CHD7, encoding a chromatin-remodeling protein, cause idiopathic hypogonadotropic hypogonadism and Kallmann syndrome

CHARGE syndrome and Kallmann syndrome (KS) are two distinct developmental disorders sharing overlapping features of impaired olfaction and hypogonadism. KS is a genetically heterogeneous disorder consisting of idiopathic hypogonadotropic hypogonadism (IHH) and anosmia, and is most commonly due to KAL1 or FGFR1 mutations. CHARGE syndrome, a multisystem autosomal-dominant disorder, is caused by CHD7 mutations. We hypothesized that CHD7 would be involved in the pathogenesis of IHH and KS (IHH/KS) without the CHARGE phenotype and that IHH/KS represents a milder allelic variant of CHARGE syndrome. Mutation screening of the 37 protein-coding exons of CHD7 was performed in 101 IHH/KS patients without a CHARGE phenotype. In an additional 96 IHH/KS patients, exons 6-10, encoding the conserved chromodomains, were sequenced. RT-PCR, SIFT, protein-structure analysis, and in situ hybridization were performed for additional supportive evidence. Seven heterozygous mutations, two splice and five missense, which were absent in > or = 180 controls, were identified in three sporadic KS and four sporadic normosmic IHH patients. Three mutations affect chromodomains critical for proper CHD7 function in chromatin remodeling and transcriptional regulation, whereas the other four affect conserved residues, suggesting that they are deleterious. CHD7's role is further corroborated by specific expression in IHH/KS-relevant tissues and appropriate developmental expression. Sporadic CHD7 mutations occur in 6% of IHH/KS patients. CHD7 represents the first identified chromatin-remodeling protein with a role in human puberty and the second gene to cause both normosmic IHH and KS in humans. Our findings indicate that both normosmic IHH and KS are mild allelic variants of CHARGE syndrome and are caused by CHD7 mutations.

Fibroblast growth factor 8 signaling through fibroblast growth factor receptor 1 is required for the emergence of gonadotropin-releasing hormone neurons

GnRH neurons are essential for the onset and maintenance of reproduction. Mutations in both fibroblast growth factor receptor (Fgfr1) and Fgf8 have been shown to cause Kallmann syndrome, a disease characterized by hypogonadotropic hypogonadism and anosmia, indicating that FGF signaling is indispensable for the formation of a functional GnRH system. Presently it is unclear which stage of GnRH neuronal development is most impacted by FGF signaling deficiency. GnRH neurons express both FGFR1 and -3; thus, it is also unclear whether FGFR1 or FGFR3 contributes directly to GnRH system development. In this study, we examined the developing GnRH system in mice deficient in FGF8, FGFR1, or FGFR3 to elucidate the individual contribution of these FGF signaling components. Our results show that the early emergence of GnRH neurons from the embryonic olfactory placode requires FGF8 signaling, which is mediated through FGFR1, not FGFR3. These data provide compelling evidence that the developing GnRH system is exquisitely sensitive to reduced levels of FGF signaling. Furthermore, Kallmann syndrome stemming from FGF signaling deficiency may be due primarily to defects in early GnRH neuronal development prior to their migration into the forebrain.

Mutations in prokineticin 2 and prokineticin receptor 2 genes in human gonadotrophin-releasing hormone deficiency: molecular genetics and clinical spectrum

CONTEXT

Mice deficient in prokineticin 2(PROK2) and prokineticin receptor2 (PROKR2) exhibit variable olfactory bulb dysgenesis and GnRH neuronal migration defects reminiscent of human GnRH deficiency.

OBJECTIVES

We aimed to screen a large cohort of patients with Kallmann syndrome (KS) and normosmic idiopathic hypogonadotropic hypogonadism (IHH) for mutations in PROK2/PROKR2, evaluate their prevalence, define the genotype/phenotype relationship, and assess the functionality of these mutant alleles in vitro.

DESIGN

Sequencing of the PROK2 and PROKR2 genes was performed in 170 KS patients and 154 nIHH. Mutations were examined using early growth response 1-luciferase assays in HEK 293 cells and aequorin assays in Chinese hamster ovary cells.

RESULTS

Four heterozygous and one homozygous PROK2 mutation (p.A24P, p.C34Y, p.I50M, p.R73C, and p.I55fsX1) were identified in five probands. Four probands had KS and one nIHH, and all had absent puberty. Each mutant peptide impaired receptor signaling in vitro except the I50M. There were 11 patients who carried a heterozygous PROKR2 mutation (p.R85C, p.Y113H, p.V115M, p.R164Q, p.L173R, p.W178S, p.S188L, p.R248Q, p.V331M, and p.R357W). Among them, six had KS, four nIHH, and one KS proband carried both a PROKR2 (p.V115M) and PROK2 (p.A24P) mutation. Reproductive phenotypes ranged from absent to partial puberty to complete reversal of GnRH deficiency after discontinuation of therapy. All mutant alleles appear to decrease intracellular calcium mobilization; seven exhibited decreased MAPK signaling, and six displayed decreased receptor expression. Nonreproductive phenotypes included fibrous dysplasia, sleep disorder, synkinesia, and epilepsy. Finally, considerable variability was evident in family members with the same mutation, including asymptomatic carriers.

CONCLUSION

Loss-of-function mutations in PROK2 and PROKR2 underlie both KS and nIHH.

Genetic control of pubertal timing

PURPOSE OF REVIEW

Puberty is an important developmental and life stage that leads to sexual maturation and reproductive capability. Although the physiology of puberty is similar among individuals, the timing of puberty is quite variable and affected by environmental and genetic influences. Identification of the responsible genetic factors will greatly enhance the understanding of the key components and the modulation of the hypothalamic-pituitary-gonadal axis.

RECENT FINDINGS

Genetic analyses are increasingly elucidating the genetic basis of pathological abnormalities in pubertal timing, including causes of idiopathic hypogonadotropic hypogonadism and Kallmann syndrome. Ongoing studies are also investigating the genetic control of puberty in the general population, although no definitive association between genetic variants and variations in pubertal timing has been discovered so far.

SUMMARY

This review summarizes recent advances regarding the genetic control of pubertal timing and presents areas for future investigation.

Decreased FGF8 signaling causes deficiency of gonadotropin-releasing hormone in humans and mice

Idiopathic hypogonadotropic hypogonadism (IHH) with anosmia (Kallmann syndrome; KS) or with a normal sense of smell (normosmic IHH; nIHH) are heterogeneous genetic disorders associated with deficiency of gonadotropin-releasing hormone (GnRH). While loss-of-function mutations in FGF receptor 1 (FGFR1) cause human GnRH deficiency, to date no specific ligand for FGFR1 has been identified in GnRH neuron ontogeny. Using a candidate gene approach, we identified 6 missense mutations in FGF8 in IHH probands with variable olfactory phenotypes. These patients exhibited varied degrees of GnRH deficiency, including the rare adult-onset form of hypogonadotropic hypogonadism. Four mutations affected all 4 FGF8 splice isoforms (FGF8a, FGF8b, FGF8e, and FGF8f), while 2 mutations affected FGF8e and FGF8f isoforms only. The mutant FGF8b and FGF8f ligands exhibited decreased biological activity in vitro. Furthermore, mice homozygous for a hypomorphic Fgf8 allele lacked GnRH neurons in the hypothalamus, while heterozygous mice showed substantial decreases in the number of GnRH neurons and hypothalamic GnRH peptide concentration. In conclusion, we identified FGF8 as a gene implicated in GnRH deficiency in both humans and mice and demonstrated an exquisite sensitivity of GnRH neuron development to reductions in FGF8 signaling.

Cytokine properties of prokineticins

Prokineticins are a novel family of secreted peptides with diverse regulatory roles, one of which is their capacity to modulate immunity in humans and in other species. Prokineticins are small peptides of 8 kDa that mediate their biological activities by signaling through two homologous G-protein-coupled receptors (prokineticin receptor 1 and prokineticin receptor 2). This family of peptides is characterized by a completely conserved N-terminal hexapeptide crucial for their bioactivities and a unique structural motif comprising five disulfide bonds. Prokineticins and their receptors are highly expressed in bone marrow, in peripheral circulating leukocytes, in inflamed tissues and in resident organ immune cells. Their structure, size, signaling and biological activities are reminiscent of the chemokine superfamily. In this review, emphasis is placed on the properties of prokineticins as cytokines and their role in the immune system.

Homozygous mutation in the prokineticin-receptor2 gene (Val274Asp) presenting as reversible Kallmann syndrome and persistent oligozoospermia: case report

Prokineticin 2 (Prok2) or prokineticin-receptor2 (Prok-R2) gene mutations are associated with Kallmann syndrome (KS). We describe a new homozygous mutation of Prok-R2 gene in a man displaying KS with an apparent reversal of hypogonadism. The proband, offspring of consanguineous parents, presented at age 19 years with absent puberty, no sense of smell, low testosterone and gonadotrophin levels. Magnetic resonance imaging showed olfactory bulb absence. The patient achieved virilization and spermatogenesis with gonadotrophin administration. Two years after discontinuing hormonal therapy, he maintained moderate oligozoospermia and normal testosterone levels. Prok2 and Prok-R2 gene sequence analyses were performed. The proband had a homozygous mutation in Prok-R2 exon 2 that harbours the c.T820>A base substitution, causing the introduction of an aspartic acid in place of valine at position 274 (Val274Asp). His mother had the same mutation in heterozygous state. This report describes a novel homozygous mutation of Prok-R2 gene in a man with variant KS, underlying the role of Prok-R2 gene in the olfactory and reproductive system development in humans. Present findings indicate that markedly delayed activation of gonadotrophin secretion may occur in some KS cases with definite gene defects, and that oligozoospermia might result from a variant form of reversible hypogonadotrophic hypogonadism.

Kisspeptin and GPR54: discovery of a novel pathway in reproduction

In order to find novel modulators of gonadotrophin-releasing hormone (GnRH) secretion, genetic tools were employed in patients with idiopathic hypogonadotrophic hypogonadism (IHH). Mutations in a G-protein coupled receptor, GPR54, were identified, making this receptor a genetic determinant and indisputable gatekeeper of normal reproductive function. This article places these investigations into historical context and reviews some of the new findings relevant to this pathway.

A review of Kallmann syndrome: genetics, pathophysiology, and clinical management

Kallmann syndrome is a genetic disorder with the hallmarks of anosmia and hypogonadotrophic hypogonadism. It has a male preponderance. With the elucidation of the genetic pathways involved, affected females and inheritance patterns are becoming more clearly identified. It is an eminently treatable disorder, but it must first be recognized by the physician. With treatment, favorable reproductive outcomes can be attained in addition to maturation of secondary sex characteristics.

Kallmann's syndrome: a comparison of the reproductive phenotypes in men carrying KAL1 and FGFR1/KAL2 mutations

CONTEXT

Kallmann's syndrome (KS) is a genetically heterogeneous disorder consisting of congenital hypogonadotropic hypogonadism (CHH) with anosmia or hyposmia.

OBJECTIVE

Our objective was to compare the reproductive phenotypes of men harboring KAL1 and FGFR1/KAL2 mutations.

DESIGN AND PATIENTS

We studied the endocrine features reflecting gonadotropic-testicular axis function in 39 men; 21 had mutations in KAL1 and 18 in FGFR1/KAL2, but none had additional mutations in PROK-2 or PROKR-2 genes.

RESULTS

Puberty failed to occur in the patients with KAL1 mutations, all of whom had complete CHH. Three patients with FGFR1/KAL2 mutations had normal puberty, were eugonadal, and had normal testosterone and gonadotropin levels. Cryptorchidism was more frequent (14 of 21 vs. 3 of 15; P<00.1) and testicular volume (2.4+/-1.1 vs. 5.4+/-2.4 ml; P<0.001) was smaller in CHH subjects with KAL1 mutations than in subjects with FGFR1/KAL2 mutations. The mean basal plasma FSH level (0.72+/-0.47 vs. 1.48+/-0.62 IU/liter; P<0.05), serum inhibin B level (19.3+/-10.6 vs. 39.5+/-19.3 pg/ml; P<0.005), basal LH plasma level (0.57+/-0.54 vs. 1.0+/-0.6 IU/liter; P<0.01), and GnRH-stimulated LH plasma level (1.2+/-1.0 vs. 4.1+/-3.5 IU/liter; P<0.01) were significantly lower in the subjects with KAL1 mutations. LH pulsatility was studied in 13 CHH subjects with KAL1 mutations and seven subjects with FGFR1/KAL2 mutations; LH secretion was nonpulsatile in all the subjects, but mean LH levels were lower in those with KAL1 mutations.

CONCLUSION

KAL1 mutations result in a more severe reproductive phenotype than FGFR1/KAL2 mutations. The latter are associated with a broader spectrum of pubertal development and with less severe impairment of gonadotropin secretion.

Role of Bv8 in neutrophil-dependent angiogenesis in a transgenic model of cancer progression

The secreted Bv8 protein has been recently characterized as a regulator of myeloid cell mobilization and a neutrophil-derived mediator of tumor angiogenesis in several xenografts, but its role in tumor progression in an endogenous setting was unknown. The rat insulin promoter (RIP)-T-antigen (Tag) is a well characterized transgenic mouse model of multistage pancreatic beta-cell tumorigenesis. Also, the role of neutrophils in RIP-Tag angiogenic switching, as assessed by systemic ablation using anti-Gr1 antibodies at different stages of tumor progression, has been recently described. Here, we show that early treatment of RIP-Tag mice with anti-Bv8 antibodies resulted in a significant reduction in the number of angiogenic islets relative to control antibody-treated mice, implicating Bv8 in the angiogenic switch during neoplasia. Histological analysis showed a significant reduction in vascular surface areas in hyperplastic and angiogenic lesions in pancreatic islets from anti-Bv8-treated mice. Anti-Bv8 treatment also inhibited the mobilization and homing of CD11b+Gr1+ cells to the peripheral blood and the emerging neoplastic lesions. However, anti-Bv8 treatment had no effect on tumor vascularization or burden when initiated at later stages of tumor progression. The stage-dependent efficacy of anti-Bv8 treatment appears remarkably similar to that reported after neutrophil ablation, suggesting that Bv8 is an important mediator of neutrophil-dependent angiogenesis in this transgenic model. In summary, our studies verify a role for Bv8 in the mobilization and recruitment of myeloid cells and in the induction of tumor angiogenesis in the early stages of neoplastic progression.

Clinical manifestations of impaired GnRH neuron development and function

Gonadotropin-releasing hormone (GnRH) and olfactory neurons migrate together in embryologic development, and disruption of this process causes idiopathic hypogonadotropic hypogonadism (IHH) with anosmia (Kallmann syndrome (KS)). Patients with IHH/KS generally manifest irreversible pubertal delay and subsequent infertility due to deficient pituitary gonadotropins or GnRH. The molecular basis of IHH/KS includes genes that: (1) regulate GnRH and olfactory neuron migration; (2) control the synthesis or secretion of GnRH; (3) disrupt GnRH action upon pituitary gonadotropes, or (4) interfere with pituitary gonadotropin synthesis or secretion. KS patients may also have midline facial defects indicating the diverse developmental functions of genes involved. Most causative genes cause either normosmic IHH or KS except FGFR1, which may cause either phenotype. Recently, several balanced chromosomal translocations have been identified in IHH/KS patients, which could lead to the identification of new disease-producing genes. Although there are two cases reported who have digenic disease, this awaits confirmation in future larger studies. The challenge will be to determine the importance of these genes in the 10-15% of couples with normal puberty who have infertility.

Síndrome de Kallmann: uma revisão histórica, clínica e molecular

A síndrome de Kallmann (SK) é a associação de hipogonadismo hipogonadotrófico (HH) e anosmia descrita por Maestre de San Juan, em 1856, e caracterizada como condição hereditária por Franz Josef Kallmann, em 1944. Muitos aspectos de sua patogenia, variabilidade fenotípica e genotípica foram desvendados nos últimos 15 anos. Conseqüentemente, tem sido difícil manter-se atualizado frente à rapidez que o conhecimento dessa condição é gerado. Nesta revisão, resgatamos aspectos históricos pouco conhecidos sobre a síndrome e seus descobridores; incorporamos novas descobertas relacionadas à embriogênese dos neurônios olfatórios e produtores de GnRH. Esse processo é fundamental para compreender a associação de hipogonadismo e anosmia; descrevemos a heterogeneidade fenotípica e genotípica, incluindo mutações em cinco genes (KAL-1, FGFR1, PROKR2, PROK2 e NELF). Para cada gene, discutimos a função da proteína codificada na migração e maturação dos neurônios olfatórios e GnRH a partir de estudos in vitro e modelos experimentais e descrevemos características clínicas dos portadores dessas mutações.

Diversity in fibroblast growth factor receptor 1 regulation: learning from the investigation of Kallmann syndrome

The unravelling of the genetic basis of the hypogonadotrophic hypogonadal disorders, including Kallmann syndrome (KS), has led to renewed interest into the developmental biology of gonadotrophin-releasing hormone (GnRH) neurones and, more generally, into the molecular mechanisms of reproduction. KS is characterised by the association of GnRH deficiency with diminished olfaction. Until recently, only two KS-associated genes were known: KAL1 and KAL2. KAL1 encodes the cell membrane and extracellular matrix-associated secreted protein anosmin-1 which is implicated in the X-linked form of KS. Anosmin-1 shows high affinity binding to heparan sulphate (HS) and its function remains the focus of ongoing investigation, although a role in axonal guidance and neuronal migration, which are processes essential for normal GnRH ontogeny and olfactory bulb histogenesis, has been suggested. KAL2, identified as the fibroblast growth factor receptor 1 (FGFR1) gene, has now been recognised to be the underlying genetic defect for an autosomal dominant form of KS. The diverse signalling pathways initiated upon FGFR activation can elicit pleiotropic cellular responses depending on the cellular context. Signalling through FGFR requires HS for receptor dimerisation and ligand binding. Current evidence supports a HS-dependent interaction between anosmin-1 and FGFR1, where anosmin-1 serves as a co-ligand activator enhancing the signal activity, the finer details of whose mechanism remain the subject of intense investigation. Recently, mutations in the genes encoding prokineticin 2 (PK2) and prokineticin receptor 2 (PKR2) were reported in a cohort of KS patients, further reinforcing the view of KS as a multigenic trait involving divergent pathways. Here, we review the historical and current understandings of KS and discuss the latest findings from the molecular and cellular studies of the KS-associated proteins, and describe the evidence that suggests convergence of several of these pathways during normal GnRH and olfactory neuronal ontogeny.

New genes controlling human reproduction and how you find them

The neuroendocrine control of reproduction in all mammals is governed by a hypothalamic neural network of approximately 1,500 gonadotropin releasing hormone (GnRH) secreting neurons that control activity of the reproductive axis across life. Recently, the syndrome of human GnRH deficiency, either with anosmia, termed Kallmann Syndrome (KS), or with a normal sense of smell, termed normosmic Idiopathic Hypogonadotropic Hypogonadism (nIHH), have proven important disease models that have revealed much about the abnormalities that can befall the GnRH neurons as they differentiate, migrate, form networks, mature and senesce. Mutations in several genes responsible for these highly coordinated developmental processes have thus been unearthed by the study of this prismatic disease model. This paper discusses several of the more important discoveries in this rapidly evolving field and puts them into a developmental and physiologic context.

Biological function of prokineticins

Secreted peptides have been implicated in diverse physiological functions. Prokineticins are a pair of regulatory peptides that signal through two highly homologous G protein-coupled receptors. Prokineticins possess a unique structural motif of five disulfide bonds and conserved N-terminal stretches. Diverse biological functions, ranging from development to adult physiology, have been attributed to prokineticins. Herein we provide an overview of current knowledge of this interesting pair of regulatory peptides.

Genetics of puberty

BACKGROUND

Puberty is controlled by genetic and environmental factors. This review examines the genetic basis for puberty by evaluating known gene mutations associated with disordered puberty in humans. At present, at least 17 different single-gene mutations are recognized as being associated with delayed or absent puberty in humans. Several of these genes are involved in the development of the olfactory nervous system, with mutations typically resulting in anosmia/hyposmia and hypogonadotropic hypogonadism, otherwise known as Kallmann syndrome. The biological basis for the association between smell and fertility is strong as development of the gonadotropin-releasing hormone (GnRH) neurons, responsible for regulating fertility, is intricately associated with development of the olfactory system. Other gene mutations, including the recently discovered kisspeptin-GPR54 signalling system, affect puberty by directly or indirectly modulating the functioning of the GnRH neurons and pituitary gonadotrophs. Together, these single-gene mutations are presently estimated to account for approximately 30% of individuals with disorders of puberty.

CONCLUSIONS

A large number of different genes are involved in the complex process of bringing about reproductive competency. In addition to the genetic mutations associated with precocious and delayed puberty, the oligogenic aetiology of these conditions is being increasingly appreciated.

Olfactory bulb hypoplasia in Prokr2 null mice stems from defective neuronal progenitor migration and differentiation

New neurons are added on a daily basis to the olfactory bulb (OB) of a mammal, and this phenomenon exists throughout its lifetime. These new cells are born in the subventricular zone and migrate to the OB via the rostral migratory stream (RMS). To examine the role of the prokineticin receptor 2 (Prokr2) in neurogenesis, we created a Prokr2 null mouse, and report a decrease in the volume of its OB and also a decrease in the number of bromodeoxyuridine (BrdU)-positive cells. There is disrupted architecture of the OB, with the glomerular layer containing terminal dUTP nick-end labeling (TUNEL) -positive nuclei and also a decrease in tyrosine hydroxylase-positive neurons in this layer. In addition, there are increased numbers of doublecortin-positive neuroblasts in the RMS and increased PSA-NCAM (polysialylated form of the neural cell adhesion molecule) -positive neuronal progenitors around the olfactory ventricle, indicating their detachment from homotypic chains is compromised. Finally, in support of this, Prokr2-deficient cells expanded in vitro as neurospheres are incapable of migrating towards a source of recombinant human prokineticin 2 (PROK2). Together, these findings suggest an important role for Prokr2 in OB neurogenesis.

From nose to fertility: the long migratory journey of gonadotropin-releasing hormone neurons

Gonadotropin-releasing hormone (GnRH) neurons, a small number of cells dispersed in the hypothalamic region of the basal forebrain, play an important role in reproductive function. These neurons originate in the nasal placode and migrate, first in the nasal compartment, then through the cribriform plate and finally through the basal forebrain, before they attain their positions in the hypothalamus. Their movement through changing molecular environments suggests that numerous factors are involved in different phases of their migration. In humans, failure of GnRH neurons to migrate normally results in delayed or absent pubertal maturation and infertility. Advances in genetic and molecular biologic techniques in this decade have allowed us to gain insights into several molecules that affect the migration of GnRH neurons and, consequently, play a role in the establishment and maintenance of reproductive function.

Loss-of-function mutation in the prokineticin 2 gene causes Kallmann syndrome and normosmic idiopathic hypogonadotropic hypogonadism

Gonadotropin-releasing hormone (GnRH) deficiency in the human presents either as normosmic idiopathic hypogonadotropic hypogonadism (nIHH) or with anosmia [Kallmann syndrome (KS)]. To date, several loci have been identified to cause these disorders, but only 30% of cases exhibit mutations in known genes. Recently, murine studies have demonstrated a critical role of the prokineticin pathway in olfactory bulb morphogenesis and GnRH secretion. Therefore, we hypothesize that mutations in prokineticin 2 (PROK2) underlie some cases of KS in humans and that animals deficient in Prok2 would be hypogonadotropic. One hundred IHH probands (50 nIHH and 50 KS) with no known mutations were examined for mutations in the PROK2 gene. Mutant PROK2s were examined in functional studies, and the reproductive phenotype of the Prok2(-/-) mice was also investigated. Two brothers with KS and their sister with nIHH harbored a homozygous deletion in the PROK2 gene (p.[I55fsX1]+[I55fsX1]). Another asymptomatic brother was heterozygous for the deletion, whereas both parents (deceased) had normal reproductive histories. The identified deletion results in a truncated PROK2 protein of 27 amino acids (rather than 81 in its mature form) that lacks bioactivity. In addition, Prok2(-/-) mice with olfactory bulb defects exhibited disrupted GnRH neuron migration, resulting in a dramatic decrease in GnRH neuron population in the hypothalamus as well as hypogonadotropic hypogonadism. Homozygous loss-of-function PROK2 mutations cause both KS and nIHH.

Bv8/Prokineticin proteins and their receptors

The Bv8/Prokineticins (PKs) are a new family of peptides identified in frog, fish, reptiles and mammals that signal through two highly homologous G-protein coupled receptors, PKR1 and PKR2. Bv8/PK proteins possess a unique structural motif comprising five disulfide bonds and a completely conserved N-terminal hexapeptide sequence that is essential for the peptide's biological activities. Over the past few years, several biological functions of Bv8/PK proteins have been elucidated. This review considers all the published data on the action and physiological role of this new biological system implicated in angiogenesis and neurogenesis, in reproduction and cancer and in regulating physiological functions that underly circadian rhythms, such as the sleep/wake cycle, hormone secretion and ingestive behaviors. The high expression level of human Bv8/PK2 in bone marrow, lymphoid organs and leukocytes suggested an involvement of these peptides in hematopoiesis and in inflammatory and immunomodulatory processes. Our review highlights the role of the Bv8/PK and their receptor system in setting the pain threshold under normal and pathological conditions.

[Diagnosis of delayed puberty]

Puberty is the phenomenon that conducts once to reproductive maturation. Delayed puberty (DP) is defined by the absence of testicular development in boys beyond 14 years old (or a testicular volume lower than 4 ml) and by the absence of breast development in girls beyond 13 years old. DP occurs in approximatively 3% of cases. Most cases are functional DP, with a large amount of constitutional delay of puberty. Others etiologies are hypogonadotrophic hypogonadism like Kallmann syndrome, or hypergonadotrophic hypogonadism. Turner syndrome is a diagnostic one should not forget by its frequency. Treatment is hormonal replacement therapy and of the etiology. During the last decade, many genes have been identified and elucidated the etiological diagnosis of some hypogonadotrophic hypogonadism syndrome. Further studies are required in collaboration with molecular biologists to better understand the mechanism of hypothalamic pituitary gonadal axis abnormalities and of the neuroendocrine physiology of the onset of puberty.

Human genetics of GPR54

Idiopathic hypogonadotropic hypogonadism (IHH) is a condition characterized by absence of sexual maturation in the setting of low sex steroids and low/normal gonadotropins. Despite its rarity, considerable genetic heterogeneity and phenotypic variability exists in this disorder. Loss of function mutations in a G protein coupled receptor, GPR54, have been shown to cause IHH. Although mutations in GPR54 are not a common cause of this condition, patients bearing mutations are critical to explore genotype-phenotype correlations and gene function. In this review, we will examine the human genetics studies of GPR54, the phenotypic implications of mutations in this gene, and the emerging roles of the kisspeptin/GPR54 pathway.

Potential roles of the prokineticins in reproduction

Prokineticins are multifunctional secreted proteins that were originally identified as regulators of intestinal contraction but subsequently shown to affect vascular function, hyperalgesia, spermatogenesis, neuronal survival, circadian rhythm, nociception, feeding behaviour, immune responses, haematopoiesis and the development of the olfactory and gonadotropin-releasing hormone systems. Their role in the reproductive tract is still not fully elucidated, although they are reputed to increase microvascular permeability. Expression of prokineticins and their receptors has been reported in the ovary, uterus, placenta, testis and prostate. Their expression has also been reported in various pathologies of the reproductive tract, and future studies will highlight whether inhibition of prokineticin function in these pathologies would be a useful therapeutic target.

Digenic mutations account for variable phenotypes in idiopathic hypogonadotropic hypogonadism

Idiopathic hypogonadotropic hypogonadism (IHH) due to defects of gonadotropin-releasing hormone (GnRH) secretion and/or action is a developmental disorder of sexual maturation. To date, several single-gene defects have been implicated in the pathogenesis of IHH. However, significant inter- and intrafamilial variability and apparent incomplete penetrance in familial cases of IHH are difficult to reconcile with the model of a single-gene defect. We therefore hypothesized that mutations at different IHH loci interact in some families to modify their phenotypes. To address this issue, we studied 2 families, one with Kallmann syndrome (IHH and anosmia) and another with normosmic IHH, in which a single-gene defect had been identified: a heterozygous FGF receptor 1 (FGFR1) mutation in pedigree 1 and a compound heterozygous gonadotropin-releasing hormone receptor (GNRHR) mutation in pedigree 2, both of which varied markedly in expressivity within and across families. Further candidate gene screening revealed a second heterozygous deletion in the nasal embryonic LHRH factor (NELF) gene in pedigree 1 and an additional heterozygous FGFR1 mutation in pedigree 2 that accounted for the considerable phenotypic variability. Therefore, 2 different gene defects can synergize to produce a more severe phenotype in IHH families than either alone. This genetic model could account for some phenotypic heterogeneity seen in GnRH deficiency.

Prokineticin receptor 2 (Prokr2) is essential for the regulation of circadian behavior by the suprachiasmatic nuclei

The suprachiasmatic nucleus (SCN), the brain's principal circadian pacemaker, coordinates adaptive daily cycles of behavior and physiology, including the rhythm of sleep and wakefulness. The cellular mechanism sustaining SCN circadian timing is well characterized, but the neurochemical pathways by which SCN neurons coordinate circadian behaviors remain unknown. SCN transplant studies suggest a role for (unidentified) secreted factors, and one potential candidate is the SCN neuropeptide prokineticin 2 (Prok2). Prok2 and its cognate prokineticin receptor 2 (Prokr2/Gpcr73l1) are widely expressed in both the SCN and its neural targets, and Prok2 is light-regulated. Hence, they may contribute to cellular timing within the SCN, entrainment of the clock, and/or they may mediate circadian output. We show that a targeted null mutation of Prokr2 disrupts circadian coordination of the activity cycle and thermoregulation. Specifically, mice lacking Prokr2 lost precision in timing the onset of nocturnal locomotor activity; and under both a light/dark cycle and continuous darkness, there was a pronounced temporal redistribution of activity away from early to late circadian night. Moreover, the coherence of circadian behavior was significantly reduced, and nocturnal body temperature was depressed. Entrainment by light is not, however, dependent on Prokr2, and bioluminescence real-time imaging of organotypical SCN slices showed that the mutant SCN is fully competent as a circadian oscillator. We conclude that Prokr2 is not necessary for SCN cellular timekeeping or entrainment, but it is an essential link for coordination of circadian behavior and physiology by the SCN, especially in defining the onset and maintenance of circadian night.

Genetic insights into human isolated gonadotropin deficiency

The identification of naturally occurring genetic mutations has provided unique insight into the current knowledge of the human hypothalamic-pituitary-gonadal axis. In the past decade, several monogenic causes have been reported in patients with isolated gonadotropin deficiency. Kallmann Syndrome is a clinically and genetically heterogeneous disorder, characterized by isolated hypogonadotropic hypogonadism and anosmia or hyposmia. To date, loss-of-function mutations in the genes encoding anosmin-1 (KAL1) and fibroblast growth factor receptor 1 (FGFR1) have been described in the X-linked and autosomal dominant forms of this syndrome, respectively. More recently, several heterozygous, homozygous or compound heterozygous mutations in the G protein-coupled prokineticin receptor-2 (PROKR2) and one of its ligands, prokineticin-2 (PROK2) were described in Kallmann syndrome. In addition, complex genetic transmission (digenic inheritance) was recently demonstrated in this condition. Regarding isolated hypogonadotropic hypogonadism without olfactory abnormalities, loss-of-function mutations in the Gonadotropin-releasing hormone (GnRH) receptor (GnRH-R) or the G-protein coupled receptor 54 (GPR54) genes, both encoding transmembrane receptors, have been described, as well as FGFR1 mutations. Finally, mutations of the beta sub-units of LH and FSH have been described in patients with selective gonadotropin deficiency. We review the role of these distinct genetic factors in human isolated hypogonadotropic hypogonadism.

The prokineticins: a novel pair of regulatory peptides

Secreted peptides play broad regulatory roles in brain function and elsewhere in the body. Prokineticins are a pair of newly identified regulatory peptides that signal through two highly homologous G protein-coupled receptors. Prokineticins possess a unique structural motif of five disulfide bonds and a completely conserved N-terminal hexapeptide sequence that is essential to biological activity. Diverse biological functions, including roles in development and cell differentiation, have been assigned to the prokineticins. A network of genes, subject to various transcriptional factors, may functionally converge on the prokineticins as regulatory targets.