Inactivating NHLH2 Variants Cause Idiopathic Hypogonadotropic Hypogonadism and Obesity in Humans

Metabolism has a role in determining the time of pubertal development and fertility. Nonetheless, molecular/cellular pathways linking metabolism/body weight to puberty/reproduction are unknown. The KNDy (Kisspeptin/Neurokinin B/Dynorphin) neurons in the arcuate (ARC) nucleus of the hypothalamus constitute the GnRH (Gonadotrophin-releasing hormone) pulse generator. We previously created a mouse model with a whole-body targeted deletion of nescient helix-loop-helix 2 (Nhlh2; N2KO), a class II member of the basic helix-loop-helix (bHLH) family of transcription factors. As this mouse model features pubertal failure and late-onset obesity, we wanted to study whether NHLH2 represents a candidate molecule to link metabolism and puberty in the hypothalamus. Exome sequencing of a large Idiopathic Hypogonadotropic Hypogonadism (IHH) cohort revealed obese patients with rare sequence variants in NHLH2, which were characterized by in silico protein analysis, chromatin immunoprecipitation, and luciferase reporter assays. In vitro heterologous expression studies demonstrated that the variant p.R79C impairs Nhlh2 binding to the Mc4r promoter. Furthermore, p.R79C and other variants show impaired transactivation of the human KISS1 promoter. These are the first inactivating human variants that support NHLH2’s critical role in human puberty and body weight control. Failure to carry out this function results in the absence of pubertal development and late-onset obesity in humans.

Genetic Etiology of Idiopathic Hypogonadotropic Hypogonadism

Idiopathic hypogonadotropic hypogonadism (IHH) is a group of rare developmental disorders characterized by low gonadotropin levels in the face of low sex steroid hormone concentrations. IHH is practically divided into two major groups according to the olfactory function: normal sense of smell (normosmia) nIHH, and reduced sense of smell (hyposmia/anosmia) Kallmann syndrome (KS). Although mutations in more than 50 genes have been associated with IHH so far, only half of those cases were explained by gene mutations. Various combinations of deleterious variants in different genes as causes of IHH have been increasingly recognized (Oligogenic etiology). In addition to the complexity of inheritance patterns, the spontaneous or sex steroid-induced clinical recovery from IHH, which is seen in approximately 10–20% of cases, blurs further the phenotype/genotype relationship in IHH, and poses challenging steps in new IHH gene discovery. Beyond helping for clinical diagnostics, identification of the genetic mutations in the pathophysiology of IHH is hoped to shed light on the central governance of the hypothalamo-pituitary-gonadal axis through life stages. This review aims to summarize the genetic etiology of IHH and discuss the clinical and physiological ramifications of the gene mutations.

DLG2 mutations in the etiology of pubertal delay and Idiopathic Hypogonadotropic Hypogonadism

Introduction: Idiopathic Hypogonadotropic hypogonadism (IHH) is caused by dysfunction of the hypothalamic-pituitary-gonadal axis. DLG2 was recently implicated as a gene associated with delayed puberty and which may also contribute to IHH. The confirmation of the candidate puberty genes in independent IHH cohorts has become crucial due to the lack proper genotype phenotype segregations in reported pedigrees. Therefore, we aimed to screen DLG2 in patients variants in a large cohort of IHH patients. Methods: The present study included a total of 336 IHH patients from 290 independent families. The coding and flanking regions of the DLG2 were screened for potentially important variants in the WES data. Candidate variants were evaluated in the gnomAD and GME databases according to their allele frequencies, and only those with a frequency <0.0001 were considered rare. Detected variants were classified according to the ACMG/AMP criteria. Results: We found one homozygous and two heterozygous missense variants in three independent pedigrees. Identified variants were found extremely rare or not reported in gnomAD. Two variants were categorized as “uncertain significance” the other one was “likely pathogenic” according to the ACMG criteria. All patients were normosmic, and in two of the three families there were no causal variants in other IHH-related genes. Conclusion: We detected three rare sequencing variants in DLG2 in five patients with IHH or delayed puberty in a large IHH cohort. Our results support the contention that the DLG2 mutations are associated with IHH in human puberty.

A novel heterozygous mutation of CHD7 gene in a Chinese patient with Kallmann syndrome: a case report

Background Variants of chromodomain helicase DNA binding protein 7 (CHD7) gene are commonly associated with Kallmann syndrome (KS) and account for 5–6% of idiopathic hypogonadotropic hypogonadism (IHH) cases. Here we report a novel mutation of CHD7 gene in a patient with KS, which may contribute to the better understanding of KS. Case presentation A 29-year-old male patient with KS and a chief complaint of delayed puberty for 13 years (Tanner B Stage< 4) was admitted to the Department of Endocrinology of the First Affiliated Hospital of Zhejiang University (Hangzhou, China) in September 2019. Dual-energy X-ray absorptiometry (DEXA) showed low bone density in both lumbar spine (L1 ~ L5 mean Z-score − 3.0) and femoral neck (Z-score − 2.7). Dynamic contrast-enhanced magnetic resonance imaging (MRI) of pituitary and contrast-enhanced computed tomography (CT) showed no abnormal findings. Ophthalmological evaluation showed that his both eyes showed exotropia, and no sight loss was noted. Heterozygous c.1619G > T mutation of TCD7 gene (p.G4856V) was detected, whereas none of his family members had this mutation. Human chorionic gonadotropin (HCG) and human menopausal gonadotropin (HMG) were injected for three times/week to treat idiopathic hypogonadotropic hypogonadism (IHH). After several months of therapy, the patient’s health condition improved. His testicles became larger, and his secondary sexual characteristics improved after treatment. Conclusion Exploration of the novel splice-site mutation of CHD7 may further our current understanding of KS.

Unilaterally Disrupted Structural and Functional Connectivity of The Fronto-Iimbic System In Idiopathic Hypogonadotropic Hypogonadism

Background: Idiopathic hypogonadotropic hypogonadism (IHH) is rare and can either be associated with normal or defective olfactory sensation, classified as normosmic IHH (nIHH) or Kallmann’s syndrome (KS), respectively. We do not yet understand the central processing pathways in the olfactory system, especially regarding these disorders. We aimed to compare the resting-state structural and functional connectivity (FC) of olfactory neural pathways in patients with nIHH and KS.Methods: A total of 50 males were studied: 13 nIHH patients, 12 KS patients, and 25 healthy controls (HCs). All subjects underwent diffusion tensor imaging (DTI) and functional magnetic resonance imaging (fMRI) scans. Structural and functional connectivity data analyses were then performed.Results: The results indicated that fractional anisotropy (FA) was significantly decreased in the right uncinate fasciculus (UF) in the KS group. The olfactory cortex FC values of the right gyrus rectus and orbitofrontal cortex (OFC) in the KS group were decreased compared with those in the HC group and increased compared with those in the nIHH group (nIHH< KS <HC). Moreover, there were significant negative correlations between right UF FA and olfactory cortex FC to both the gyrus rectus and OFC within the nIHH and HC groups.Conclusion: We have reported significant structural and functional disruptions unilaterally at the right junction of the fronto-limbic system in KS patients. The results may indicate that a specific structural-functional asymmetry exists in the olfactory cortex pathways in KS patients.

Contribution of Copy Number Variation in Idiopathic Hypogonadotropic Hypogonadism

Introduction: While the role of single nucleotide variants (SNVs) in causal genes for Idiopathic Hypogonadotropic hypogonadism (IHH) is known, the contribution of copy number variants (CNVs) to IHH has not been systematically studied. Here, we examined the prevalence of CNVs in a large IHH cohort and their associated phenotypic spectrum. Methods: Exome sequencing (ES) from 1,441 IHH probands was analyzed using the GATK-gCNV pipeline to identify CNVs that spanned known IHH genes with a site frequency of &lt;1%. ES data was also analyzed for rare SNVs in all IHH genes. IHH subjects were evaluated for reproductive and non-reproductive phenotypes (kidney, eye, cardiovascular, midline/ facial, bone and neurological abnormalities). Results: (i) CNV prevalence in IHH: Three percent of the IHH probands (46/1441 probands, 38 males and 8 females) harbored CNVs in 19/36 high confidence IHH genes (26 deletions 20 duplications). The vast majority of CNVs disrupted either the ANOS1 (26%) or FGFR1 (17%) genes. Intriguingly, CHD7 (a gene that carries SNVs in ~12% of our IHH subjects) did not harbor any CNVs. (ii) Phenotypic analysis: We found that CNVs were more common in IHH subjects with anosmia (Kallmann syndrome, N=33) compared to normosmic IHH (N=13). More than half of the subjects with CNVs affecting IHH genes carried at least 1 non-reproductive feature (26/46 IHH subjects, 56%). A syndromic presentation with multiple non-reproductive phenotypes was more common in IHH subjects harboring multigenic CNVs (IHH gene & additional genes) compared to IHH subjects with single IHH gene CNV or SNV in a single IHH gene (61% vs. 12% or 18%, respectively; p 0.0006). Conclusions: CNVs in known IHH genes contribute to 3% of the IHH genetic architecture in our cohort. IHH subjects with larger multigenic CNVs displayed phenotypes consistent with contiguous gene syndromes. The absence of genic CNVs in genes frequently found to carry SNVs, such as CHD7, requires additional analysis to establish the biologic or mechanistic reasons for their rarity.

Idiopathic hypogonadotropic hypogonadism: a rare cause of primary amenorrhoea in adolescence—a review and update on diagnosis, management and advances in genetic understanding.

Idiopathic hypogonadotropic hypogonadism (IHH) refers to a family of genetic disorders that affect the production and/or action of gonadotropic-releasing hormone, resulting in reduced serum levels of sex steroids. This condition has a prevalence of 1–10 cases/100 000 births and is characterised by the absence of spontaneous pubertal development. In women, the condition is characterised by the onset of normal adrenarche, with the absence of thelarche and menarche. Pubertal induction for breast development and uterine growth with oestradiol, and sequential maintenance of a normal menstrual cycle and adequate oestrogen for bone health, with an oestrogen and progesterone, is considered first-line treatment. Pregnancy can be achieved in patients who have received and responded to treatment with ovulation induction with exogenous gonadotrophins. Advances in genetic testing have led to increased research and understanding of the underlying genetics of IHH with gene mutations described in up to 50% of all IHH cases.