Isolated familial hypogonadotropic hypogonadism and a GNRH1 mutation

Clinical genetics of 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 (KAL1). 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 (KAL2). 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 autosomal recessive monogenic (KAL3) and digenic/oligogenic KS transmission modes. 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. Notably, KS may also be part of pleiotropic developmental diseases including CHARGE syndrome; this disease results in most cases from neomutations in CHD7 that encodes a chromodomain helicase DNA-binding protein.

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.

A comparative phenotypic study of kallmann syndrome patients carrying monoallelic and biallelic mutations in the prokineticin 2 or prokineticin receptor 2 genes

CONTEXT

Both biallelic and monoallelic mutations in PROK2 or PROKR2 have been found in Kallmann syndrome (KS).

OBJECTIVE

The objective of the study was to compare the phenotypes of KS patients harboring monoallelic and biallelic mutations in these genes.

DESIGN AND PATIENTS

We studied clinical and endocrine features that reflect the functioning of the pituitary-gonadal axis, and the nonreproductive phenotype, in 55 adult KS patients (42 men and 13 women), of whom 41 had monoallelic mutations and 14 biallelic mutations in PROK2 or PROKR2.

RESULTS

Biallelic mutations were associated with more frequent cryptorchidism (70% vs. 34%, P < 0.05) and microphallus (90% vs. 28%, P < 0.001) and lower mean testicular volume (1.2 +/- 0.4 vs. 4.5 +/- 6.0 ml; P < 0.01) in male patients. Likewise, the testosterone level as well as the basal FSH level and peak LH level under GnRH-stimulation were lower in males with biallelic mutations (0.2 +/- 0.1 vs. 0.7 +/- 0.8 ng/ml; P = 0.05, 0.3 +/- 0.1 vs. 1.8 +/- 3.0 IU/liter; P < 0.05, and 0.8 +/- 0.8 vs. 5.2 +/- 5.5 IU/liter; P < 0.05, respectively). Nonreproductive, nonolfactory anomalies were rare in both sexes and were never found in patients with biallelic mutations. The mean body mass index of the patients (23.9 +/- 4.2 kg/m(2) in males and 26.3 +/- 6.6 kg/m(2) in females) did not differ significantly from that of gender-, age-, and treatment-matched KS individuals who did not carry a mutation in PROK2 or PROKR2. Finally, circadian cortisol levels evaluated in five patients, including one with biallelic PROKR2 mutations, were normal in all cases.

CONCLUSION

Male patients carrying biallelic mutations in PROK2 or PROKR2 have a less variable and on average a more severe reproductive phenotype than patients carrying monoallelic mutations in these genes. Nonreproductive, nonolfactory clinical anomalies associated with KS seem to be restricted to patients with monoallelic mutations.

Heterozygous orthodenticle homeobox 2 mutations are associated with variable pituitary phenotype

CONTEXT

Although recent studies have suggested a positive role of OTX2 in pituitary as well as ocular development and function, detailed pituitary phenotypes in OTX2 mutations and OTX2 target genes for pituitary function other than HESX1 and POU1F1 remain to be determined.

OBJECTIVE

We aimed to examine such unresolved issues.

SUBJECTS

We studied 94 Japanese patients with various ocular or pituitary abnormalities.

RESULTS

We identified heterozygous p.K74fsX103 in case 1, p.A72fsX86 in case 2, p.G188X in two unrelated cases (3 and 4), and a 2,860,561-bp microdeletion involving OTX2 in case 5. Clinical studies revealed isolated GH deficiency in cases 1 and 5; combined pituitary hormone deficiency in case 3; abnormal pituitary structures in cases 1, 3, and 5; and apparently normal pituitary function in cases 2 and 4, together with ocular anomalies in cases 1-5. The wild-type Orthodenticle homeobox 2 (OTX2) protein transactivated the GNRH1 promoter as well as the HESX1, POU1F1, and IRBP (interstitial retinoid-binding protein) promoters, whereas the p.K74fsX103-OTX2 and p.A72fsX86-OTX2 proteins had no transactivation functions and the p.G188X-OTX2 protein had reduced ( approximately 50%) transactivation functions for the four promoters, with no dominant-negative effect. cDNA screening identified positive OTX2 expression in the hypothalamus.

CONCLUSIONS

The results imply that OTX2 mutations are associated with variable pituitary phenotype, with no genotype-phenotype correlations, and that OTX2 can transactivate GNRH1 as well as HESX1 and POU1F1.

Idiopathic hypogonadotropic hypogonadism in a mother and her monozygotic twins born after a single embryo transfer

OBJECTIVE

To describe a mother with idiopathic hypogonadotropic hypogonadism (IHH) and her monozygotic (MZ) twin boys who all have the same heterozygous fibroblast growth factor receptor-1 (FGFR1) gene mutation.

DESIGN

Case report.

SETTING

University hospital.

PATIENT(S)

A 28-year-old mother with normosmic IHH gave birth to MZ twin boys after a transfer of a single frozen-thawed embryo.

INTERVENTION(S)

Clinical and biochemical evaluation of IHH. Sequence analysis of the 17 coding exons (exons 2-18) and exon-intron boundaries of FGFR1 from polymerase chain reaction-amplified genomic DNA from peripheral blood leukocytes of the subjects.

MAIN OUTCOME MEASURE(S)

Phenotypic features of the subjects.

RESULT(S)

All subjects harbored a previously undescribed heterozygous FGFR1 mutation (c.2049-1 G-->C), leading to the skipping of exon 16 and thus a loss of amino acids 684-726 in the tyrosine kinase domain of the receptor. The absence of exon 16 was verified at the cDNA level. The twins manifested with microphallus, cryptorchidism, and deficient postnatal activation of the hypothalamic-pituitary-gonadal axis, findings consistent with IHH.

CONCLUSION(S)

Our report underlines that assisted reproductive techniques enable the inheritance of gene mutations causing infertility. This is the first report on the phenotypic features of MZ twins with an FGFR1 mutation.

Human GnRH deficiency: a unique disease model to unravel the ontogeny of GnRH neurons

Evolutionary survival of a species is largely a function of its reproductive fitness. In mammals, a sparsely populated and widely dispersed network of hypothalamic neurons, the gonadotropin-releasing hormone (GnRH) neurons, serve as the pilot light of reproduction via coordinated secretion of GnRH. Since it first description, human GnRH deficiency has been recognized both clinically and genetically as a heterogeneous disease. A spectrum of different reproductive phenotypes comprised of congenital GnRH deficiency with anosmia (Kallmann syndrome), congenital GnRH deficiency with normal olfaction (normosmic idiopathic hypogonadotropic hypogonadism), and adult-onset hypogonadotropic hypogonadism has been described. In the last two decades, several genes and pathways which govern GnRH ontogeny have been discovered by studying humans with GnRH deficiency. More importantly, detailed study of these patients has highlighted the emerging theme of oligogenicity and genotypic synergism, and also expanded the phenotypic diversity with the documentation of reversal of GnRH deficiency later in adulthood in some patients. The underlying genetic defect has also helped understand the associated nonreproductive phenotypes seen in some of these patients. These insights now provide practicing clinicians with targeted genetic diagnostic strategies and also impact on clinical management.

Steroidogenesis in the fetal testis and its susceptibility to disruption by exogenous compounds

Masculinization depends on adequate production of testosterone by the fetal testis within a specific "masculinization programming window." Disorders resulting from subtle deficiencies in this process are common in humans, and environmental exposures/lifestyle could contribute causally because common therapeutic and environmental compounds can affect steroidogenesis. This evidence derives mainly from rodent studies, but because there are major species differences in regulation of steroidogenesis in the fetal testis, this may not always be a guide to potential effects in the human. In addition to direct study of the effects of compounds on steroidogenesis, information also derives from study of masculinization disorders that result from mutations in genes in pathways regulating steroidogenesis. This review addresses this issue by critically reviewing the comparative timing of production and regulation of steroidogenesis in the fetal testis of humans and of rodents and its susceptibility to disruption; where there is limited information for the fetus, evidence from effects on steroidogenesis in the adult testis is considered. There are a number of fundamental regulatory differences between the human and rodent fetal testis, most notably in the importance of paracrine vs. endocrine drives during masculinization such that inactivating LH receptor mutations block masculinization in humans but not in rodents. Other large differences involve the steroidogenic response to estrogens and GnRH analogs and possibly phthalates, whereas for other compounds there may be differences in sensitivity to disruption (ketoconazole). This comparison identifies steroidogenic targets that are either vulnerable (mitochondrial cholesterol transport, CYP11A, CYP17) or not (cholesterol uptake) to chemical interference.

Hypogonadotropic hypogonadism due to a novel missense mutation in the first extracellular loop of the neurokinin B receptor

CONTEXT

The neurokinin B (NKB) receptor, encoded by TACR3, is widely expressed within the central nervous system, including hypothalamic nuclei involved in regulating GnRH release. We have recently reported two mutations in transmembrane segments of the receptor and a missense mutation in NKB in patients with normosmic isolated hypogonadotropic hypogonadism (nIHH).

PATIENTS AND METHODS

We sequenced the TACR3 gene in a family in which three siblings had nIHH. The novel mutant receptor thus identified was studied in a heterologous expression system using calcium flux as the functional readout.

RESULTS

All affected siblings were homozygous for the His148Leu mutation, in the first extracellular loop of the NKB receptor. The His148Leu mutant receptor exhibited profoundly impaired signaling in response to NKB (EC(50) = 3 +/- 0.1 nm and >5 microm for wild-type and His148Leu, respectively). The location of the mutation in an extracellular part of the receptor led us also to test whether senktide, a synthetic NKB analog, may retain ability to stimulate the mutant receptor. However, the signaling activity of the His148Leu receptor in response to senktide was also severely impaired (EC(50) = 1 +/- 1 nm for wild-type and no significant response of His148Leu to 10 microm).

CONCLUSIONS

Homozygosity for the TACR3 His148Leu mutation leads to failure of sexual maturation in humans, whereas signaling by the mutant receptor in vitro in response to either NKB or senktide is severely impaired. These observations further strengthen the link between NKB, the NKB receptor, and regulation of human reproductive function.

The mammalian ovary from genesis to revelation

Two major functions of the mammalian ovary are the production of germ cells (oocytes), which allow continuation of the species, and the generation of bioactive molecules, primarily steroids (mainly estrogens and progestins) and peptide growth factors, which are critical for ovarian function, regulation of the hypothalamic-pituitary-ovarian axis, and development of secondary sex characteristics. The female germline is created during embryogenesis when the precursors of primordial germ cells differentiate from somatic lineages of the embryo and take a unique route to reach the urogenital ridge. This undifferentiated gonad will differentiate along a female pathway, and the newly formed oocytes will proliferate and subsequently enter meiosis. At this point, the oocyte has two alternative fates: die, a common destiny of millions of oocytes, or be fertilized, a fate of at most approximately 100 oocytes, depending on the species. At every step from germline development and ovary formation to oogenesis and ovarian development and differentiation, there are coordinated interactions of hundreds of proteins and small RNAs. These studies have helped reproductive biologists to understand not only the normal functioning of the ovary but also the pathophysiology and genetics of diseases such as infertility and ovarian cancer. Over the last two decades, parallel progress has been made in the assisted reproductive technology clinic including better hormonal preparations, prenatal genetic testing, and optimal oocyte and embryo analysis and cryopreservation. Clearly, we have learned much about the mammalian ovary and manipulating its most important cargo, the oocyte, since the birth of Louise Brown over 30 yr ago.

Diagnosis of diseases of steroid hormone production, metabolism and action

Biochemical tests have been the basis for investigations of disorders affecting steroid hormones. In recent years it has been possible however to study the genes that determine functional enzymes, cofactors, receptors, transcription factors and signaling systems that are involved in the process. Analyses of mutations are available as a diagnostic service for only a few of these genes although research laboratories may be able to provide a service. Both biochemical and genetic research have brought to light new disorders. Some genes for transcription factors involved in the development of the endocrine organs have also been identified and patients with defects in these processes have been found. This paper will review general aspects of adrenal disorders with emphasis on clinical and laboratory findings. As with all endocrine investigations there are few single measurements that provide a definitive answer to a diagnosis. Timing of samples in relation to age, gender and time of day needs to be considered.

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.