Hypogonadotropic hypogonadism.

Gonadotropin-releasing hormone (GnRH) and olfactory neurons migrate together from the olfactory placode, and GnRH neurons eventually reside in the hypothalamus. Hypogonadism in male infants may be diagnosed in the first 6 months of life but cannot be diagnosed during childhood until puberty occurs. Patients with low serum testosterone and low serum gonadotropin levels have idiopathic hypogonadotropic hypogonadism (IHH). Mutations in three genes (KAL1, FGFR1, and GNRHR) comprise most of the known genetic causes of IHH. Treatment with testosterone is indicated if fertility is not desired, whereas GnRH or gonadotropin treatment induces spermatogenesis and fertility.     

Role of sequence variations of the GnRH receptor and G protein-coupled receptor 54 gene in male idiopathic hypogonadotropic hypogonadism

OBJECTIVE: To determine the frequency of mutations of the gonadotropin-releasing hormone receptor (GnRHR) and of the G protein-coupled receptor 54 (GPR54) genes in normosmic idiopathic hypogonadotropic hypogonadism (IHH). METHODS: In a retrospective study we analyzed the GnRHR and the GPR54 genes of 45 IHH patients and 50 controls. Genomic DNA was amplified by PCR to obtain partially overlapping amplicons encompassing the exon-intron boundaries of the GnRHR and GPR54 genes and analyzed by single-stranded conformation polymorphism gel electrophoresis and/or DNA sequencing. RESULTS: One heterozygous R262Q mutation of the GnRHR gene was identified in one patient with familial IHH. The silent single-nucleotide polymorphism (SNP) 453C > T occurred at the same frequency in patients and controls. One patient with sporadic IHH and consanguineous parents showed a novel homozygous sequence variation of the GPR54 gene (1001_1002insC) resulting in an open reading frame shift and elongation of 43 amino acids with an increased number of proline residues in the intracellular receptor domain. This patient had delayed puberty, low testosterone (3.4 nmol/l), and low-normal LH and FSH levels responsive to GnRH. Pulsatile GnRH administration normalized testosterone levels and induced spermatogenesis sufficiently to induce a pregnancy with assisted reproduction. Two common SNPs in exon 1 and exon 5 of the GPR54 gene showed similar frequency distribution and hormonal profiles in IHH and controls. CONCLUSIONS: Mutations of the GnRHR and of the GPR54 gene are rare in IHH and should be investigated especially in cases with autosomal recessive transmission. Common SNPs of the GnRHR and GPR54 genes do not play any role in IHH.     

Prevalence, phenotypic spectrum, and modes of inheritance of gonadotropin-releasing hormone receptor mutations in idiopathic hypogonadotropic hypogonadism

Mutations in the GnRH receptor (GNRHR) have been described as a cause of reproductive failure in a subset of patients with idiopathic hypogonadotropic hypogonadism (IHH). Given the apparent rarity of these mutations, we set out to determine the frequency and distribution of GNRHR mutations in a heterogeneous population of patients with IHH who were well characterized with respect to diagnosis, phenotype, and mode of inheritance and to define their distribution within the receptor protein. One hundred and eight probands with IHH were screened for mutations in the coding sequence of GNRHR. Forty-eight of the 108 patients had a normal sense of smell, whereas the remaining 60 had anosmia or hyposmia (Kallmann syndrome). Exon segments in the GNRHR were screened for mutations using temperature gradient gel electrophoresis, and all mutations were confirmed by direct sequencing. Five unrelated probands (3 men and 2 women), all normosmic, were documented to have changes in the coding sequence of the GNRHR. Two of these probands were from a subgroup of 5 kindreds consistent with a recessive mode of inheritance, establishing a GNRHR mutation frequency of 2 of 5 (40%) in patients with normosmic, autosomal recessive IHH. The remaining 3 probands with GNRHR mutations were from a subgroup of 18 patients without evidence of familial involvement, indicating a prevalence of 3 of 18 (16.7%) in patients with sporadic IHH and a normal sense of smell. Among the five individuals bearing GNRHR mutations, a broad spectrum of phenotypes was noted, including testicular sizes in the male that varied from prepubertal to the normal adult male range. Three probands had compound heterozygous mutations, and two had homozygous mutations. Of the eight DNA sequence changes identified, four were novel: Thr(32)Ile, Cys(200)Tyr, Leu(266)Arg, and Cys(279)TYR: COS-7 cells transiently transfected with complementary DNAs encoding the human GNRHR containing each of these four novel mutations failed to respond to GnRH agonist stimulation. We conclude that 1) the spectrum of phenotypes in patients with GNRHR mutations is much broader than originally anticipated; 2) the frequency of GNRHR mutations may be more common than previously appreciated in familial cases of normosmic IHH and infrequent in sporadic cases; and 3) functional mutations of the GNRHR are distributed widely throughout the protein.     

Genetics of hypogonadotropic hypogonadism

Determining the physiologic influences that modulate GnRH secretion, the prime initiator of reproductive function in the human, is fundamental not only to our understanding of the rare condition of congenital idiopathic hypogonadotropic hypogonadism (IHH), but also common disorders such as constitutional delay of puberty and hypothalamic amenorrhea. IHH is characterized by low levels of sex steroids and gonadotropins, normal findings on radiographic imaging of the hypothalamic-pituitary regions, and normal baseline and reserve testing of the remainder of the hypothalamic-pituitary axes. Failure of the normal pattern of episodic GnRH secretion results in delay of puberty and infertility. IHH is characterized by rich clinical and genetic heterogeneity, variable modes of inheritance, and association with other anomalies. To date, 4 genes have been identified as causes of IHH in the human; KAL [the gene for X-linked Kallmann syndrome (IHH and anosmia)], DAX1 [the gene for X-linked adrenal hypoplasia congenita (IHH and adrenal insufficiency)], GNRHR (the GnRH receptor), and PC1 (the gene for prohormone convertase 1, causing a syndrome of IHH and defects in prohormone processing). As these mutations account for less than 20% of all IHH cases, discovery of additional gene mutations will continue to advance our understanding of this intriguing syndrome.     

Isolated cryptorchidism: no evidence for involvement of genes underlying isolated hypogonadotropic hypogonadism

Mutations in FGFR1, GNRHR, PROK2, PROKR2, TAC3, or TACR3 underlie isolated hypogonadotropic hypogonadism (IHH) with clinically variable phenotypes, and, by causing incomplete intrauterine activation of the hypothalamic-pituitary-gonadal axis, may lead to cryptorchidism. To investigate the role of defects in these genes in the etiology of isolated cryptorchidism, we screened coding exons and exon-intron boundaries of these genes in 54 boys or men from 46 families with a history of cryptorchidism. Control subjects (200) included 120 males. None of the patients carried mutation(s) in FGFR1, PROK2, PROKR2, TAC3 or TACR3. Two of the 46 index subjects with unilateral cryptorchidism were heterozygous carriers of a single GNRHR mutation (Q106R or R262Q), also present in male controls with a similar frequency (3/120; p=0.62). No homozygous or compound heterozygous GNRHR mutations were found. In conclusion, cryptorchidism is not commonly caused by defects in genes involved in IHH.     

Autosomal recessive idiopathic hypogonadotropic hypogonadism: genetic analysis excludes mutations in the gonadotropin-releasing hormone (GnRH) and GnRH receptor genes

Failure of the normal pattern of episodic secretion of GnRH from the hypothalamus results in the clinical syndrome of idiopathic hypogonadotropic hypogonadism (IHH), with failure of pubertal development and infertility. The only gene that has been implicated in normosmic IHH is the GnRH receptor gene (GNRHR), which accounts for 10% of cases. This report presents four families with autosomal recessive IHH, including a consanguineous pedigree from the Middle East. Defects within the genomic coding sequence of the GNRHR, and the GnRH gene itself, GNRH1, were excluded by temperature gradient gel electrophoresis, direct sequencing, and haplotypes created from simple sequence polymorphisms flanking the GNRH1 and GNRHR loci. We concluded that: 1) genetic analysis has excluded sequence variations in GNRH1 and GNRHR in four families with recessive IHH, suggesting the existence of a novel, as-yet-undiscovered gene for this condition, and 2) because mutation analysis of genomic coding sequence will fail to detect mutations deep within introns or regulatory regions, haplotype analysis is the preferred genetic methodology to eliminate the role of specific candidate genes.     

Distinguishing constitutional delay of growth and puberty from isolated hypogonadotropic hypogonadism: critical appraisal of available diagnostic tests

Context: Determining the etiology of delayed puberty during initial evaluation can be challenging. Specifically, clinicians often cannot distinguish constitutional delay of growth and puberty (CDGP) from isolated hypogonadotropic hypogonadism (IHH), with definitive diagnosis of IHH awaiting lack of spontaneous puberty by age 18 yr. However, the ability to make a timely, correct diagnosis has important clinical implications. Objective: The aim was to describe and evaluate the literature regarding the ability of diagnostic tests to distinguish CDGP from IHH. Evidence Acquisition: A PubMed search was performed using key words "puberty, delayed" and "hypogonadotropic hypogonadism," and citations within retrieved articles were reviewed to identify studies that assessed the utility of basal and stimulation tests in the diagnosis of delayed puberty. Emphasis was given to a test's ability to distinguish prepubertal adolescents with CDGP from those with IHH. Evidence Synthesis: Basal gonadotropin and GnRH stimulation tests have limited diagnostic specificity, with overlap in gonadotropin levels between adolescents with CDGP and IHH. Stimulation tests using more potent GnRH agonists and/or human chorionic gonadotropin may have better discriminatory value, but small study size, lack of replication of diagnostic thresholds, and prolonged protocols limit clinical application. A single inhibin B level in two recent studies demonstrated good differentiation between groups. Conclusion: Distinguishing IHH from CDGP is an important clinical issue. Basal inhibin B may offer a simple, discriminatory test if results from recent studies are replicated. However, current literature does not allow for recommendation of any diagnostic test for routine clinical use, making this an important area for future investigation.     

Mutations in fibroblast growth factor receptor 1 cause both Kallmann syndrome and normosmic idiopathic hypogonadotropic hypogonadism

Mutations in KAL1 and FGFR1 cause Kallmann syndrome (KS), whereas mutations in the GNRHR and GPR54 genes cause idiopathic hypogonadotropic hypogonadism with normal olfaction (nIHH). Mixed pedigrees containing both KS and nIHH have also been described; however, the genetic cause of these rare cases is unknown. We examined the FGFR1 gene in seven nIHH subjects who either belonged to a mixed pedigree (n = 5) or who had associated midline defects (n = 2). Heterozygous FGFR1 mutations were found in three of seven unrelated nIHH probands with normal MRI of the olfactory system: (i) G237S in an nIHH female and a KS brother; (ii) (P722H and N724K) in an nIHH male missing two teeth and his mother with isolated hyposmia; and (iii) Q680X in a nIHH male with cleft lip/palate and missing teeth, his brother with nIHH, and his father with delayed puberty. We show that these mutations lead to receptor loss-of-function. The Q680X leads to an inactive FGFR1, which lacks a major portion of the tyrosine kinase domain (TKD). The G237S mutation inhibits proper folding of D2 of the FGFR1 and likely leads to the loss of cell-surface expression of FGFR1. In contrast, the (P722H and N724K) double mutation causes structural perturbations in TKD, reducing the catalytic activity of TKD. We conclude that loss-of-function mutations in FGFR1 cause nIHH with normal MRI of the olfactory system. These mutations also account for some of the mixed pedigrees, thus challenging the current idea that KS and nIHH are distinct entities.     

Kisspeptin/GPR54与特发性低促性腺激素性性腺功能减退症

特发性低促性腺激素性性腺功能减退症(IHH)主要表现为促性腺激素水平低下和性成熟障碍.迄今,对IHH的病因和发病机制了解甚少.近年来,在部分IHH家系中发现了G蛋白耦联受体54(GPR54)基因突变,进一步研究提示GPR54及其配体kisspeptin参与促性腺激素释放激素(GnRH)的分泌调节.Kisspeptin可以直接促进下丘脑GnRH分泌、介导性激素对GnRH的反馈调节,以及参与青春期肩动等.因此认为,Kisspeptin/GPR54的基因突变是导致IHH的病因之一,同时kisspeptin/GPR54对下丘脑-垂体-性腺轴的正常功能起到重要参与作用.     

GnRH receptor and GPR54 inactivation in isolated gonadotropic deficiency

Isolated hypogonadotropic hypogonadism (IHH) is defined by a complete or partial impaired secretion of luteinizing hormone (LH) and follicle-stimulating hormone (FSH). In the regulation of the gonadotropic axis, the gonadotropin-releasing hormone (GnRH) and its receptor have evolved as a central element in fetal life, at puberty, and for reproduction in adulthood. GnRH resistance due to GnRH receptor (GnRHR) germ-line mutations was the first genetic alteration identified in patients with IHH. GnRHR mutated receptors are associated with impaired GnRH binding, intracellular trafficking or ligand-induced signal transduction, leading to various degrees of LH and FSH deficiency. Loss-of-function mutations of the GnRH receptor account for 50% of familial cases of IHH without anosmia. In 2003, mutations of GPR54 were identified in patients with IHH, opening a new pathway in the physiological regulation of puberty and reproduction. Kisspeptins, which are the natural ligands of GPR54, are potent stimulators of the LH and FSH secretion via the control of GnRH secretion or modulation of the pituitary response to GnRH stimulation. Genotype-phenotype correlations in IHH due to GnRHR and GPR54 mutations indicate that similar mutations may lead to a variable phenotype and suggest that the pituitary might have its own pubertal maturation independent from GnRH. These two causes of IHH result in a more quantitative than qualitative defect of the gonadotropic axis activation. Molecular genetics of IHH has led to a major breakthrough in the neuroendocrine regulation of the gonadotropic axis. New insights into the understanding of the initiation of puberty and in the therapeutic management of defects of the gonadotropic axis have emerged from these studies.     

GnRH receptor mutations in isolated gonadotropic deficiency

GnRH and its receptor GnRHR are key regulators of the hypothalamo-pituitary axis. They modulate the secretion of LH and FSH gonadotropins and therefore, the development and maturation of gonads in fetal life as well as after birth. Congenital functional defect of this axis results in isolated hypogonadotropic hypogonadism (IHH). Several natural mutations causing IHH without anosmia have now been identified in GnRHR or GnRH genes. These mutations inactivate GnRHR or its ligand function and cause highly variable phenotypes, ranging from partial to complete gonadotropic deficiencies. The present review describes the published natural GnRHR mutations and tries to correlate them with the corresponding phenotypes according to the different steps of the GnRH system development.     

Reversible kallmann syndrome, delayed puberty, and isolated anosmia occurring in a single family with a mutation in the fibroblast growth factor receptor 1 gene

Kallmann syndrome (KS) is a clinically and genetically heterogeneous disorder. Recently, loss-of-function mutations in the fibroblast growth factor receptor 1 (FGFR1) gene have been shown to cause autosomal dominant KS. To date, the detailed reproductive phenotype of KS associated with mutations in the FGFR1 has yet to be described. We report a kindred comprising a male proband with KS and spontaneous reversibility, whose mother had delayed puberty and whose maternal grandfather isolated anosmia. The proband presented at age 18 yr with KS and was subsequently treated with testosterone (T) therapy. Upon discontinuation of T therapy, he recovered from his hypogonadotropic hypogonadism, as evidenced by a normal LH secretion pattern, sustained normal serum T levels, and active spermatogenesis. The three members of this single family harbor the same FGFR1 mutation (Arg(622)X) in the tyrosine kinase domain. This report demonstrates 1) the first genetic cause of the rare variant of reversible KS, 2) the reversal of hypogonadotropic hypogonadism in a proband carrying an FGFR1 mutation suggests a role of FGFR1 beyond embryonic GnRH neuron migration, and 3) a loss of function mutation in the FGFR1 gene causing delayed puberty.     

Reversible Kallmann syndrome: report of the first case with a KAL1 mutation and literature review

Kallmann syndrome (KS) describes the association of isolated hypogonadotropic hypogonadism with hypo/anosmia. A few KS patients may reverse hypogonadism after testosterone withdrawal, a variant known as reversible KS. Herein, we describe the first mutation in KAL1 in a patient with reversible KS and review the literature. The proband was first seen at 22 years complaining of anosmia and lack of puberty. His brother had puberty at 30 years and a maternal granduncle had anosmia and delayed puberty. On physical examination, he was P(2)G(1), testes were 3 ml and bone age was 14 years. During 20 years of irregular testosterone replacement, he developed secondary sexual characteristics and testicular enlargement. At the age of 41 years, after stopping testosterone replacement for 5 months, his testes were 15 ml, serum testosterone, LH, and FSH responses to GnRH were normal, and his wife was pregnant. The molecular study revealed a cytosine insertion in exon 2 of KAL1, generating a frameshift at codon 75 and a premature stop at codon 85. The expected gene product is a truncated peptide with 85 of the 680 [corrected] amino acids present in the wild-type protein. Fourteen cases of reversible KS have been described but the genotype was only studied in a single case showing a heterozygous fibroblast growth factor receptor type 1 (FGFR1) mutation. Considering the low prevalence of mutations in KAL1 or FGFR1 in KS, it is possible that these genotypes are more prevalent in reversible KS than in other KS patients, but additional studies are necessary to confirm this hypothesis.     

A needle in a haystack: mutations in GNRH1 as a rare cause of isolated GnRH deficiency

GNRH1, the human gene that gives rise to GnRH, has long been an obvious candidate gene for idiopathic hypogonadotropic hypogonadism, particularly because the hpg mouse, a mouse model of isolated hypogonadotropic hypogonadism, carries a deletion that disrupts Gnrh1. In 2009, 25 years after the sequence of human GNRH1 was initially determined, two groups independently reported homozygous frameshift mutations in GNRH1 in patients with idiopathic hypogonadotropic hypogonadism. In two additional families, heterozygous GNRH1 mutations segregated with reproductive disorders. In the first family, the mutation occurred alone in five female subjects with idiopathic hypogonadotropic hypogonadism, whereas in the second it co-existed with a mutation in NR0B1/DAX1 in two female subjects with delayed puberty. While hemizygous mutations the X-linked NR0B1 are a well-known cause of hypogonadotropic hypogonadism and adrenal hypoplasia in male patients, heterozygous female carriers are generally asymptomatic. Thus, mutations in GNRH1 have been associated with both mild and severe forms of GnRH deficiency, and may work in combination with other gene mutations to produce GnRH-deficient phenotypes.     

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.     

Two novel missense mutations in g protein-coupled receptor 54 in a patient with hypogonadotropic hypogonadism

It has recently been shown that loss-of-function mutations of the G protein-coupled receptor (GPR)54 lead to isolated hypogonadotropic hypogonadism (IHH) in mice and humans. Such mutations are thought to be rare, even within the clinical IHH population, and only a handful of alleles have been described, making further screening of IHH populations imperative. We examined the genes encoding GPR54 and its putative endogenous ligand, kisspeptin-1, for mutations in a cohort of 30 patients with normosmic HH or delayed puberty. One subject with HH, of mixed Turkish-Cypriot and Afro-Caribbean ancestry, was found to be a compound heterozygote for two previously undescribed missense mutations in GPR54: cysteine 223 to arginine (C223R) in the fifth transmembrane helix and arginine 297 to leucine (R297L) in the third extracellular loop. Assessed in vitro using a previously described sensitive signaling assay in cells stably expressing GPR54, the C223R variant was found to exhibit profoundly impaired signaling, whereas the R297L variant showed a mild reduction in ligand-stimulated activity across the ligand dose range. These novel mutations provide further evidence that human HH may be caused by loss-of-function mutations in GPR54.     

Lack of gonadotropic response to pulsatile gonadotropin-releasing hormone in isolated hypogonadotropic hypogonadism associated to congenital adrenal hypoplasia

Congenital adrenal hypoplasia (AH) is a rare condition, known to be associated with isolated hypogonadotropic hypogonadism (IHH). Three studies have reported attempts to stimulate gonadotropin secretion with pulsatile gonadotropin-releasing hormone (GnRH) in a total of 4 patients presenting such a syndrome, with conflicting results. In the present study, one patient with idiopathic IHH and AH was treated with pulsatile sc GnRH--doses ranging from 2.5 to 10.0 micrograms/pulse, every 90 min--during 8 weeks in an attempt to induce puberty. The prepubertal basal plasma levels of LH, FSH and testosterone, and saliva testosterone levels remained unaltered throughout treatment, at all doses of GnRH tested. The gonadotropin response to an acute iv GnRH administration (0.1 mg) also remained at the prepubertal level after pulsatile GnRH treatment. No circulating anti-GnRH antibodies were detected. The absence of gonadotropic response to exogenous pulsatile GnRH suggests that the IHH of patients with AH is due to an abnormal pituitary function rather than to a lack of endogenous GnRH.     

Mechanisms of Disease: the first kiss-a crucial role for kisspeptin-1 and its receptor, G-protein-coupled receptor 54, in puberty and reproduction

Although the hypothalamic secretion of gonadotropin-releasing hormone (GnRH) is the defining hormonal event of puberty, the physiologic mechanisms that drive secretion of GnRH at the time of sexual maturation have been difficult to identify. After puberty is initiated, the factors that modulate the frequency and amplitude of GnRH secretion in rapidly changing sex-steroid environments (i.e. the female menstrual cycle) also remain unknown. The discovery that, in both humans and mouse models, loss-of-function mutations in the gene that encodes G-protein-coupled receptor 54 result in phenotypes of hypogonadotropic hypogonadism with an absence of pubertal development has unearthed a novel pathway regulating GnRH secretion. Ligands for G-protein-coupled receptor 54 (KiSS-1R), including metastin (derived from the parent compound, kisspeptin-1) and metastin's C-terminal peptide fragments, have been shown to be powerful stimulants for GnRH release in vivo via their stimulation of G-protein-coupled receptor 54. This article reviews the discovery of the GPR54 gene, places it into the appropriate biological context, and explores the data from in vitro and in vivo studies that point to this ligand-receptor system as a major driver of GnRH secretion.     

Resistance of hypogonadic patients with mutated GnRH receptor genes to pulsatile GnRH administration

We have studied a kindred with three siblings with isolated hypogonadotropic hypogonadism caused by compound heterozygote mutations in the GnRH receptor gene. The disorder was transmitted as an autosomal recessive trait. The R262Q mutation in intracellular loop 3 of the receptor was associated with a mutation in the third transmembrane domain of the receptor, A129D, that has never been described before. This A129D mutation results in a complete loss of function, indicated by the lack of inositol triphosphate (TP3) 3 production by transfected Chinese hamster ovary (CHO) cells after GnRH stimulation. The two brothers had microphallus and bilateral cryptorchidism and were referred for lack of puberty, whereas their sister had primary amenorrhea and a complete lack of puberty. Their basal gonadotropin concentrations were below the reference range, and their endogenous LH secretory patterns were abnormal, with a low-normal frequency of small pulses or no apparent LH pulse. Pulsatile GnRH administration (10 microg/pulse every 90 min for 40 h) resulted in increased mean LH without any significant changes in testosterone levels in the two brothers, whereas the LH secretory profile of their sister remained apulsatile. Larger pulses of exogenous GnRH (20 microg every 90 min for 24 h) caused the sister to produce recognizable low amplitude LH pulses. The concentrations of free alpha-subunit significantly increased in all patients during the pulsatile GnRH administration. Thus, these hypogonadal patients are partially resistant to pulsatile GnRH administration, suggesting that they should be treated with gonadotropins to induce spermatogenesis or ovulation rather than with pulsatile GnRH.