Leydig cell hypoplasia due to inactivation of luteinizing hormone receptor by a novel homozygous nonsense truncation mutation in the seventh transmembrane domain

Restoring function to inactivating G protein-coupled receptor variants in the hypothalamic-pituitary-gonadal axis1

G protein-coupled receptors (GPCRs) are central to the functioning of the hypothalamic-pituitary-gonadal axis (HPG axis) and include the rhodopsin-like GPCR family members, neurokinin 3 receptor, kappa-opioid receptor, kisspeptin 1 receptor, gonadotropin-releasing hormone receptor, and the gonadotropin receptors, luteinizing hormone/choriogonadotropin receptor and follicle-stimulating hormone receptor. Unsurprisingly, inactivating variants of these receptors have been implicated in a spectrum of reproductive phenotypes, including failure to undergo puberty, and infertility. Clinical induction of puberty in patients harbouring such variants is possible, but restoration of fertility is not always a realisable outcome, particularly for those patients suffering from primary hypogonadism. Thus, novel pharmaceuticals and/or a fundamental change in approach to treating these patients are required. The increasing wealth of data describing the effects of coding-region genetic variants on GPCR function has highlighted that the majority appear to be dysfunctional as a result of misfolding of the encoded receptor protein, which, in turn, results in impaired receptor trafficking through the secretory pathway to the cell surface. As such, these intracellularly retained receptors may be amenable to 'rescue' using a pharmacological chaperone (PC)-based approach. PCs are small, cell permeant molecules hypothesised to interact with misfolded intracellularly retained proteins, stabilising their folding and promoting their trafficking through the secretory pathway. In support of the use of this approach as a viable therapeutic option, it has been observed that many rescued variant GPCRs retain at least a degree of functionality when 'rescued' to the cell surface. In this review, we examine the GPCR PC research landscape, focussing on the rescue of inactivating variant GPCRs with important roles in the HPG axis, and describe what is known regarding the mechanisms by which PCs restore trafficking and function. We also discuss some of the merits and obstacles associated with taking this approach forward into a clinical setting.

A novel variant luteinizing hormone receptor in the first transmembrane helix of two homozygous Iranian patients: case report

Background

Leydig cell hypoplasia (LCH) is a rare autosomal recessive endocrine syndrome that affects the normal development of male external genitalia in 46, XY individuals and is one of the causes of disorder of sexual differentiation (DSD) in males. The responsible gene of LCH is LHCGR which is located on the chromosome 2 and its various mutations lead to different degrees of the disease ranging from micropenis to complete XY DSD.

Case presentation

In this study, we have investigated the clinical presentation and molecular findings of two siblings with complete male LCH and XY DSD. This is the first detailed report of individuals with LCH from Iran. It aimed to study the molecular and clinical characteristics of two sisters with type 1 LCH. Whole exome sequencing was used for these patients to find the underlying genetic cause of the disease. Our Iranian DSD patients had external genitalia (normal labia major and minor, the external opening of the urethra beneath the clitoris) and bilateral testicular tissues in the inguinal region, which were removed by surgical exploration.

Conclusions

Genetic sequencing showed the homozygous variants of the LHCGR gene in the patients, a novel duplication variant in exon 11, c.1091dupT -or pLeu365Profs*5. This mutation is described as likely pathogenic. We think that this case report can widen the genotypic spectrum of the LHCGR variants. Moreover, this study emphasizes the significant rule of Whole Exome Sequencing in differentiating various causes of disorder of sexual differentiation.

Novel Compound Heterozygous Variants in the LHCGR Gene in a Genetically Male Patient with Female External Genitalia

The LHCGR gene encodes a G-protein coupled receptor that plays a pivotal role in sexual differentiation in males, ovarian development in females and in fertility via its interaction with luteinizing hormone and chorionic gonadotropin. Inactive variants of the LHCGR gene cause Leydig cell hypoplasia (LCH), which is a rare disease and one of the causes of disorder of sexual differentiation (DSD) in males. The aim of this work was to clarify the clinical and molecular characteristics of a 2.75 year old patient with type 1 LCH. Whole exome sequencing was performed for the patient family and variants in the LHCGR gene were validated by Sanger sequencing. Pathogenicity of the missense variant was evaluated by multiple in silico tools. Our Chinese patient, who exhibited DSD, had female external genitalia (normal labia majora and minora, external opening of urethra under the clitoris and blind-ended vagina) and bilateral testis tissues in the inguinal region. Genetic sequencing revealed compound heterozygous variants in the LHCGR gene in the patient, including a novel missense variant in exon 4 (c.349G>A, p.Gly117Arg) and a novel nonsense variant in exon 10 (c.878C>A, p.Ser293*). The missense variant is in the first leucine-rich repeat domain of the LHCGR protein, which is predicted to affect ligand recognition and binding affinity and thus protein function. The patient is molecularly and clinically diagnosed with type 1 LCH, which is caused by novel, compound heterozygous variants of the LHCGR gene. We believe this report will serve to expand the genotypic spectrum of LHCGR variants.

The gonadotropin system, lessons from animal models and clinical cases

This review article centers upon family of gonadotropin hormones which consists of two pituitary hormones - follicle-stimulating hormone (FSH) and luteinizing hormone (LH) as well as one non-pituitary hormone - human chorionic gonadotropin (hCG) secreted by placenta, and their receptors. Gonadotropins play an essential role in proper sexual development, puberty, gametogenesis, maintenance of pregnancy and male sexual differentiation during the fetal development. They belong to the family of glycoprotein hormones thus they constitute heterodimeric proteins built of common α subunit and hormone-specific β-subunit. Hitherto, several mutations in genes encoding both gonadotropins and their receptors have been identified in humans. Their occurrence resulted in a number of different phenotypes including delayed puberty, primary amenorrhea, hermaphroditism, infertility and hypogonadism. In order to understand the effects of mutations on the phenotype observed in affected patients, detailed molecular studies are required to map the relationship between the structure and function of gonadotropins and their receptors. Nonetheless, in vitro assays are often insufficient to understand physiology. Therefore, several animal models have been developed to unravel the physiological roles of gonadotropins and their receptors.

Loss-of-Function Mutations in the Human Luteinizing Hormone Receptor Predominantly Cause Intracellular Retention

Mutations in G protein-coupled receptors (GPCRs) have been identified for many endocrine hormone signaling deficiencies. Inactivating mutations can impair ligand binding, receptor activation/coupling to signaling pathways, or can cause receptor misfolding and consequent impaired expression at the cell membrane. Here we examine the cell surface expression, ligand binding, and signaling of a range of mutant human luteinizing hormone receptors (LHRs) identified as causing reproductive dysfunction in human patients. The data obtained reveal how mutations in GPCRs can have diverse and severely deleterious effects on receptor function. Furthermore, it was found that impaired functionality of the majority of the mutant LHRs was due to reduced expression at the cell surface (14/20) while only two mutations caused impaired binding affinity and two impaired in signaling. An additional two mutations were found to cause no impairment of receptor function. These data demonstrate that the majority of LHR mutations lead to intracellular retention and highlight the potential for novel pharmacological chaperone therapeutics that can "rescue" expression/function of retained mutant GPCRs.

Novel homozygous nonsense mutations in the luteinizing hormone receptor (LHCGR) gene associated with 46,XY primary amenorrhea

OBJECTIVE

To determine the genetic cause of 46,XY primary amenorrhea in three 46,XY girls.

DESIGN

Whole exome sequencing.

SETTING

University cytogenetics center.

PATIENT(S)

Three patients with unexplained 46,XY primary amenorrhea were included in the study.

INTERVENTION(S)

Potentially pathogenic variants were confirmed by Sanger sequencing, and familial segregation was determined where parents' DNA was available.

MAIN OUTCOME MEASURE(S)

Exome sequencing was performed in the three patients, and the data were analyzed for potentially pathogenic mutations. The functional consequences of mutations were predicted.

RESULT(S)

Three novel homozygous nonsense mutations in the luteinizing hormone receptor (LHCGR) gene were identified:c.1573 C→T, p.Gln525Ter, c.1435 C→T p.Arg479Ter, and c.508 C→T, p.Gln170Ter.

CONCLUSION(S)

Inactivating mutations of the LHCGR gene may be a more common cause of 46,XY primary amenorrhea than previously considered.

Perspectives in Pediatric Pathology, Chapter 6. Male Undermasculinization

Normal male development requires three conditions: (1) adequate differentiation of the fetal testis; (2) synthesis and secretion of testicular hormones; and (3) effective action of these hormones on target organs. This requires the combined action of the inhibitory anti-müllerian hormone (AMH, secreted by Sertoli cells) to block the development of the uterus and fallopian tubes from the müllerian duct, together with the trophic stimulus of testosterone (a Leydig cell product), which leads to virilization of the wolffian ducts. Additionally, the development of external genitalia depends on the conversion of testosterone to dihydrotestosterone by the enzyme 5-α-reductase. Failure of any of these mechanisms leads to deficient virilization or the so-called "male pseudohermaphroditism" syndromes.

New insights into the genetic basis of infertility

Infertility is a disease of the reproductive system characterized by inability to achieve pregnancy after 12 or more months of regular unprotected sexual intercourse. A variety of factors, including ovulation defects, spermatogenic failure, parental age, obesity, and infections have been linked with infertility, in addition to specific karyotypes and genotypes. The study of genes associated with infertility in rodent models has expanded the field of translational genetics in identifying the underlying cause of human infertility problems. Many intriguing aspects of the molecular basis of infertility in humans remain poorly understood; however, application of genetic knowledge in this field looks promising. The growing literature on the genetics of human infertility disorders deserves attention and a critical concise summary is required. This paper provides information obtained from a systematic analysis of the literature related to current research into the genetics of infertility affecting both sexes.

Identification by array-Comparative Genomic Hybridization (array-CGH) of a large deletion of luteinizing hormone receptor gene combined with a missense mutation in a patient diagnosed with a 46,XY disorder of sex development and application to prenatal diagnosis

This paper reports the case of an infant presenting with sexual ambiguity at birth. The child presented with labia majora synechia, thready genital tubercle and perineal hypospadias. The karyotype was 46,XY. Low testosterone levels with no response to hCG administration, associated with high LH level for her age, high FSH level, high inhibin B levels and normal AMH indicated a lack of LH receptivity and prompted us to screen the LHCGR gene for mutations. A previously described missense mutation (p.Cys131Arg) was identified at homozygous state in the propositus and at heterozygous state in the mother. This variation, however, was not found in the father. Our attention was drawn by the presence of several single nucleotide polymorphisms (SNPs), identified at homozygous state without any paternal contribution from exon 1 to exon 10 of LHCGR, suggesting a paternal deletion. Array DNA analysis was performed revealing a large deletion extending from 61,493 to 135,344 bp and including the LHCGR gene. Adequate genetic counselling was provided. This paper describes the first application of prenatal diagnosis in LHCGR deficiency for 46,XY disorders of sex development with the subsequent delivery of a normal baby.

The genetic basis for the timing of human puberty

Puberty is a complex, coordinated biological process with multiple levels of regulation. Epidemiological observations suggest that the timing of pubertal events is a heritable trait, although environmental factors can modulate such genetic influence. The study of pathological states of early and late puberty has provided valuable insight into those genes that regulate gonadotrophin-releasing hormone (GnRH) activity. The development of pulsatile release of GnRH secretion mediated through kisspeptin-1 activation of G-protein coupled receptor-54 appears to be a central event at the onset and during progression of puberty. Stimulating and restraining influences (e.g. in the form of glutamatergic and GABAergic neuronal inputs) are likely to influence the timing of this process. The study of extreme variants of 'normality', such as constitutional delay of growth and puberty and early puberty, may lead to the recognition of additional genes and pathways that can modulate both the timing of pubertal onset and its tempo.

Inactivating mutations of G protein-coupled receptors and diseases: Structure-function insights and therapeutic implications

Since the discovery of the first rhodopsin mutation that causes retinitis pigmentosa in 1990, significant progresses have been made in elucidating the pathophysiology of diseases caused by inactivating mutations of G protein-coupled receptors (GPCRs). This review aims to compile the compelling evidence accumulated during the past 15 years demonstrating the etiologies of more than a dozen diseases caused by inactivating GPCR mutations. A generalized classification scheme, based on the life cycle of GPCRs, is proposed. Insights gained through detailed studies of these naturally occurring mutations into the structure-function relationship of these receptors are reviewed. Therapeutic approaches directed against the different classes of mutants are being developed. Since intracellular retention emerges as the most common defect, recent progresses aimed at correcting this defect through membrane permeable pharmacological chaperones are highlighted.

Biological effect of a novel mutation in the third leucine-rich repeat of human luteinizing hormone receptor

A novel heterozygous mutation A340T leading to the substitution of Phe for the conserved amino acid Ile114 was identified by nucleotide sequencing of the human LH/chorionic gonadotropin receptor (hLHR) of a patient with Leydig cell hypoplasia. This mutation is located in the third leucine-rich repeat in the ectodomain of the hLHR. In vitro expression studies demonstrated that this mutation results in reduced ligand binding and signal transduction of the receptor. Studies of hLHR constructs in which various amino acids were substituted for the conserved Ile114 showed that receptor activity is sensitive to changes in size, shape, and charge of the side chain. A homology model of the wild-type hLHR ectodomain was made, illustrating the packing of conserved hydrophobic side chains in the protein core. Substitution of Ile114 by Phe might disrupt intermolecular contacts between hormone and receptor. This mutation might also affect an LHR-dimer interaction. Thus, the I114F mutation reduces ligand binding and signal transduction by the hLHR, and it is partially responsible for Leydig cell hypoplasia in the patient.

An update of the pathophysiology of human gonadotrophin subunit and receptor gene mutations and polymorphisms

New information about mutations and polymorphisms in the genes for the gonadotrophins and their receptors has become available in the last few years. In this short review mutations and polymorphisms in gonadotrophins, their receptors and their pathophysiological effects and implications are discussed. An increasingly clear picture about the structure–function relationships of gonadotrophin action is emerging from the combining the types and the locations of the mutations with their phenotypic effects and the information about the crystal structure of these molecules.

Hormonal regulation of Leydig cell proliferation and differentiation in rodent testis: a dynamic interplay between gonadotrophins and testicular factors

Studies over the last few decades have documented that LH is the principal regulator of Leydig cell function. Recent studies indicate that locally produced intratesticular factors are equally important in modulating Leydig cell development and function. In the present review, results of studies on Leydig development and function with rodent models, in conjunction with recent advances in our understanding, are discussed. Studies on Leydig cell development revealed that there are two different waves of proliferation: the first one is independent of LH and the other is dependent on LH. In addition to LH, FSH plays a major role in Leydig cell development and function by modulating the production of Sertoli cell-derived factors. Studies directed towards understanding the oestrogen-mediated inhibition of Leydig cell proliferation revealed that collagen IV-mediated signalling is involved in Leydig cell proliferation and 17beta-oestradiol inhibits this event. Leydig cell proliferation and differentiation is associated with changes in gene expression. Research in this area has identified several genes that are involved in Leydig cell proliferation and differentiation; the possible role of these genes in the context of Leydig cell development are discussed in this review.