High Frequency of MKRN3 Mutations in Male Central Precocious Puberty Previously Classified as Idiopathic

Natural sweetener glycyrrhizin protects against precocious puberty by modulating the gut microbiome

AIMS

Precocious puberty (PP) may lead to many adverse outcomes. Recent evidence suggests that PP is a gut-brain disease. On the other hand, the use of glycyrrhizin, a natural sweetener, has become popular in the past decade. Glycyrrhizin possesses various health benefits, but its impact on PP has yet to be investigated. We aimed to explore the protective effects of glycyrrhizin against PP in both humans (observational) and animals (interventional).

MATERIALS AND METHODS

In the human cohort, we investigated the association between glycyrrhizin consumption and risk of PP. In the animal experiment, we observed puberty onset after feeding danazol-induced PP rats with glycyrrizin. Blood, fecal, and hypothalamic samples were harvested to evaluate potential mechanistic pathways. We also performed a fecal microbiota transplantation to confirm to causal relationship between glycyrrhizin and PP risk.

KEY FINDINGS

Glycyrrhizin exhibited a protective effect against PP in children (OR 0.60, 95%CI: 0.39-0.89, p = 0.013), primarily driven by its significance in girls, while no significant effect was observed in boys. This effect was consistent with findings in rodents. These benefits were achieved through the modulation of the gut microbiome, which functionally suppressed the hypothalamic-pituitary-gonadal axis and prevented PP progression. A fecal microbiota transplantation indicated that the causal correlation between glycyrrhizin intake and PP is mediated by the gut microbiome alterations.

SIGNIFICANCE

Our findings suggest that glycyrrhizin can protect against PP by altering the gut microbiome. Long term use of glycyrrhizin is safe and tolerable. Therefore, glycyrrhizin can serve as a safe and affordable complementary therapy for PP.

Central Precocious Puberty in Italian Boys: Data From a Large Nationwide Cohort

CONTEXT

There are only a few nationwide studies on boys with central precocious puberty (CPP) and the last Italian study is a case series of 45 boys that dates back to 2000.

OBJECTIVE

We aimed to evaluate the causes of CPP in boys diagnosed during the last 2 decades in Italy and the relative frequency of forms with associated central nervous system (CNS) abnormalities on magnetic resonance imaging (MRI) compared to idiopathic ones.

METHODS

We performed a national multicenter retrospective study collecting data from 193 otherwise normal healthy boys with a diagnosis of CPP. Based on MRI findings, the patients were divided into: Group 1, no CNS abnormalities; Group 2, mild abnormalities (incidental findings) unrelated to CPP; and Group 3, causal pathological CNS abnormalities.

RESULTS

The MRI findings show normal findings in 86%, mild abnormalities (incidental findings) in 8.3%, and causal pathological CNS abnormalities in 5.7% of the cases. In Group 3, we found a higher proportion of patients with chronological age at diagnosis < 7 years (P = .00001) and body mass index greater than +2 SDS (P < .01). Gonadotropin-releasing hormone analogue therapy was started in 183/193 subjects. The final height appeared in the range of the target height in all groups and in 9 patients in whom the therapy was not started.

CONCLUSION

In our study on a large nationwide cohort of boys referred for precocious puberty signs, the percentage of forms associated with CNS abnormalities was one of the lowest reported in the literature.

The genetic etiology is a relevant cause of central precocious puberty

OBJECTIVES

The etiology of central precocious puberty (CPP) has expanded with identification of new genetic causes, including the monogenic deficiency of Makorin-Ring-Finger-Protein-3 (MKRN3). We aimed to assess the prevalence of CPP causes and the predictors of genetic involvement in this phenotype.

DESIGN

A retrospective cohort study for an etiological survey of patients with CPP from a single academic center.

METHODS

All patients with CPP had detailed medical history, phenotyping, and brain magnetic resonance imaging (MRI); those with negative brain MRI (apparently idiopathic) were submitted to genetic studies, mainly DNA sequencing studies, genomic microarray, and methylation analysis.

RESULTS

We assessed 270 patients with CPP: 50 (18.5%) had CPP-related brain lesions (34 [68%] congenital lesions), whereas 220 had negative brain MRI. Of the latter, 174 (165 girls) were included for genetic studies. Genetic etiologies were identified in 22 patients (20 girls), indicating an overall frequency of genetic CPP of 12.6% (22.2% in boys and 12.1% in girls). The most common genetic defects were MKRN3, Delta-Like-Non-Canonical-Notch-Ligand-1 (DLK1), and Methyl-CpG-Binding-Protein-2 (MECP2) loss-of-function mutations, followed by 14q32.2 defects (Temple syndrome). Univariate logistic regression identified family history (odds ratio [OR] 3.3; 95% CI 1.3-8.3; P = .01) and neurodevelopmental disorders (OR 4.1; 95% CI 1.3-13.5; P = .02) as potential clinical predictors of genetic CPP.

CONCLUSIONS

Distinct genetic causes were identified in 12.6% patients with apparently idiopathic CPP, revealing the genetic etiology as a relevant cause of CPP in both sexes. Family history and neurodevelopmental disorders were suggested as predictors of genetic CPP. We originally proposed an algorithm to investigate the etiology of CPP including genetic studies.

Diagnosis, Treatment, and Outcomes of Males with Central Precocious Puberty

Central precocious puberty (CPP) among males is less frequent than among females but more likely to have an underlying pathologic cause. Diagnosis of CPP is often straightforward among males because increased testicular volume, the first sign of puberty, can be verified although careful central nervous system (CNS) assessment is generally necessary. Treatment with gonadotropin-releasing hormone agonist (GnRHa) is indicated, given in conjunction with any therapy needed for CNS lesions. Monitoring of treatment usually can consist of evaluating growth and physical puberty and with testosterone levels as the only lab data. Short-term and long-term outcome data indicate efficacy and safety, although data are limited. Such data need to be reported.

MKRN3 circulating levels in girls with central precocious puberty caused by MKRN3 gene mutations

PURPOSE

MKNR3 is a paternally expressed gene whose mutations are the main cause of central precocious puberty (CPP). Protein circulating levels can be easily measured, as demonstrated in idiopathic CPP and healthy controls. No data are available for patients harboring an MKRN3 mutation. Our aim was to perform MKRN3 mutation screening and to investigate if circulating protein levels could be a screening tool to identify MKRN3 mutation in CPP patients.

METHODS

We enrolled 140 CPP girls and performed MKRN3 mutation analysis. Patients were stratified into two groups: idiopathic CPP (iCPP) and MKRN3 mutation-related CPP (MKRN3-CPP). Clinical characteristics were collected. Serum MKRN3 values were measured by a commercially available ELISA assay kit in MKRN3-CPP and a subgroup of 15 iCPP patients.

RESULTS

We identified 5 patients with MKRN3 mutations: one was a novel mutation (p.Gln352Arg) while the others were previously reported (p.Arg328Cys, p.Arg345Cys, p.Pro160Cysfs*14, p.Cys410Ter). There was a significant difference in circulating MKRN3 values in MKRN3-CPP compared to iCPP (p < 0.001). In MKRN3-CPP, the subject harboring Pro160Cysfs*14 presented undetectable levels. Subjects carrying the missense mutations p.Arg328Cys and p.Gln352Arg showed divergent circulating protein levels, respectively 40.56 pg/mL and undetectable. The patient with the non-sense mutation reported low but measurable MKRN3 levels (12.72 pg/mL).

CONCLUSIONS

MKRN3 defect in patients with CPP cannot be predicted by MKRN3 circulating levels, although those patients presented lower protein levels than iCPP. Due to the great inter-individual variability of the assay and the lack of reference values, no precise cut-off can be identified to suspect MKRN3 defect.

Novel MKRN3 Missense Mutations Associated With Central Precocious Puberty Reveal Distinct Effects on Ubiquitination

CONTEXT

Loss-of-function mutations in the maternally imprinted genes, MKRN3 and DLK1, are associated with central precocious puberty (CPP). Mutations in MKRN3 are the most common known genetic etiology of CPP.

OBJECTIVE

This work aimed to screen patients with CPP for MKRN3 and DLK1 mutations and analyze the effects of identified mutations on protein function in vitro.

METHODS

Participants included 84 unrelated children with CPP (79 girls, 5 boys) and, when available, their first-degree relatives. Five academic medical institutions participated. Sanger sequencing of MKRN3 and DLK1 5' upstream flanking and coding regions was performed on DNA extracted from peripheral blood leukocytes. Western blot analysis was performed to assess protein ubiquitination profiles.

RESULTS

Eight heterozygous MKRN3 mutations were identified in 9 unrelated girls with CPP. Five are novel missense mutations, 2 were previously identified in patients with CPP, and 1 is a frameshift variant not previously associated with CPP. No pathogenic variants were identified in DLK1. Girls with MKRN3 mutations had an earlier age of initial pubertal signs and higher basal serum luteinizing hormone and follicle-stimulating hormone compared to girls with CPP without MRKN3 mutations. Western blot analysis revealed that compared to wild-type MKRN3, mutations within the RING finger domain reduced ubiquitination whereas the mutations outside this domain increased ubiquitination.

CONCLUSION

MKRN3 mutations were present in 10.7% of our CPP cohort, consistent with previous studies. The novel identified mutations in different domains of MKRN3 revealed different patterns of ubiquitination, suggesting distinct molecular mechanisms by which the loss of MRKN3 results in early pubertal onset.

[Gonadotropin-dependent precocious puberty: genetic and clinical characteristics]

BACKGROUND

In 90% cases of girls and 25-60% cases of boys the cause of gonadotropin-dependent precocious puberty (PP) is unclear. Up to 25-27.5% of gonadotropin-dependent PP cases are monogenic and suggest autosomal-dominant inheritance with incomplete sex-dependent penetrance. To date, mutations in genes KISS1, KISS1R, MKRN3, DLK1 have been described as causal variants leading to precocious hypothalamic-pituitary axis activation in childhood. Genetic testing in patients with hereditary forms of PP can expand our knowledge of underlying molecular mechanisms of the disease and it  is also necessary for genetic counselling.

AIM

To study clinical features and genetic characteristics of patients with idiopathic gonadotropin-dependent precocious puberty.

MATERIALS AND METHODS

A group of patients with idiopathic gonadotropin-dependent precocious puberty and positive family history (early or precocious puberty) was examined. Laboratory and instrumental diagnostic tests, full-exome sequencing (NGS, next-generation sequencing) were provided for all patients.

RESULTS

The study included 30 patients (29 girls, 1 boy) with idiopathic gonadotropin-dependent precocious puberty. The median of patients age at the time of the examination was 7,2 years [6,5; 7,7]. Positive family history presented in all cases: in 40% of patients on father's side, in 37% - on mother's side, in 23% of patients PP was diagnosed in siblings. The fullexome sequencing was conducted to 21 patients: in 61,9% of cases (95% CI [40;79]) nucleotide variants were identified   in genes, associated with gonadotropin-dependent precocious puberty. MKRN3 gene defect was detected in most cases (77% cases (95% CI [49; 92]), which consistent with international data on its highest prevalence in the monogenic forms of PP. In 23% of cases (95% CI [7; 50]) nucleotide variants were identified in other candidate genes associated with neuroontogenesis and neuroendocrine regulation mechanisms of hypothalamic-pituitary axis.

CONCLUSION

Our study confirms that detailed family history data in children with PP provides a rational approach to molecular-genetic testing. Data of inheritance pattern and clinical manifestations will simplify the diagnosis of hereditary forms of disease and enhance genetic counselling of families, followed by timely examination and administration of pathogenetic therapy.

Molecular analysis of MKRN3 gene in Turkish girls with sporadic and familial idiopathic central precocious puberty

OBJECTIVES

Central precocious puberty (CPP) develops as a result of early stimulation of the hypothalamic-pituitary-gonadal (HPG) axis. The loss-of-function mutations in the Makorin-ring-finger3 (MKRN3) gene appear to be the most common molecular cause of familial CPP. We aimed to identify MKRN3 gene mutations in our CPP cohort and to investigate the frequency of MKRN3 mutations.

METHODS

102 patients with CPP included. 53 of them had family history of CPP in the first and/or second-degree relatives. MKRN3 gene was analyzed by next-generation sequencing.

RESULTS

Possible pathogenic variants were found in 2/53 patients with family history of CPP (3.8%) and 1/49 patient without family history (2%). A novel heterozygous c.1A>G (p.Met1Val) mutation, a novel heterozygous c.683_684delCA (p.Ser228*) and a previously reported c.482dupC (Ala162Glyfs*) frameshift variations were detected. The two novel variants are predicted to be pathogenic in silico analyses.

CONCLUSIONS

In our cohort, possible pathogenic variants in MKRN3 gene were detected in 2.9% of the total cohort, 3.8% of the familial and 2% of the nonfamilial cases, slightly lower than that reported in the literature. Two novel variants detected contribute to the molecular repertoire of MKRN3 defects in CPP. Classical pattern of paternal inheritance has been demonstrated in all three cases. However, the father of the patient 3 did not have history of CPP suggesting that the father inherited this variant from his mother and had phenotype skipping. Therefore, we emphasize that the absence of history of CPP in the father does not exclude the possibility of a MKRN3 mutation.

Serum metabolomic analysis reveals key metabolites in drug treatment of central precocious puberty in female children

Precocious puberty (PP) is a common condition among children. According to the pathogenesis and clinical manifestations, PP can be divided into central precocious puberty (CPP, gonadotropin dependent), peripheral precocious puberty (PPP, gonadotropin independent), and incomplete precocious puberty (IPP). Identification of the variations in key metabolites involved in CPP and their underlying biological mechanisms has increased the understanding of the pathological processes of this condition. However, little is known about the role of metabolite variations in the drug treatment of CPP. Moreover, it remains unclear whether the understanding of the crucial metabolites and pathways can help predict disease progression after pharmacological therapy of CPP. In this study, systematic metabolomic analysis was used to examine three groups, namely, healthy control (group N, 30 healthy female children), CPP (group S, 31 female children with CPP), and treatment (group R, 29 female children) groups. A total of 14 pathways (the top two pathways were aminoacyl-tRNA biosynthesis and phenylalanine, tyrosine, and tryptophan biosynthesis) were significantly enriched in children with CPP. In addition, two short peptides (His-Arg-Lys-Glu and Lys-Met-His) were found to play a significant role in CPP. Various metabolites associated with different pathways including amino acids, PE [19:1(9Z)0:0], tumonoic acid I, palmitic amide, and linoleic acid-biotin were investigated in the serum of children in all groups. A total of 45 metabolites were found to interact with a chemical drug [a gonadotropin-releasing hormone (GnRH) analog] and a traditional Chinese medicinal formula (DBYW). This study helps to understand metabolic variations in CPP after drug therapy, and further investigation may help develop individualized treatment approaches for CPP in clinical practice.

A new DLK1 defect in a family with idiopathic central precocious puberty: elucidation of the male phenotype

PURPOSE

We aimed to investigate a cohort of female and male patients with idiopathic central precocious puberty (CPP), negative for Makorin Ring Finger Protein 3 (MKRN3) defect, by molecular screening for Delta-like 1 homolog (DLK1) defects. DLK1 is an imprinted gene, whose mutations have been described as a rare cause of CPP in girls and adult women with precocious menarche, obesity and metabolic derangement.

METHODS

We enrolled 14 girls with familial CPP and 13 boys with familial or sporadic CPP from multiple academic hospital centers. Gene sequencing of DLK1 gene was performed. Circulating levels of DLK1 were measured and clinical and biochemical characteristics were described in those with DLK1 defects.

RESULTS

A novel heterozygous mutation in DLK1, c.288_289insC (p.Cys97Leufs*16), was identified in a male proband, his sister and their father. Age at onset of puberty was in line with previous reports in the girl and 8 years in the boy. The father with untreated CPP showed short stature. No metabolic derangement was present in the father except hypercholesterolemia. Undetectable Dlk1 serum levels indicated the complete lack of protein production in the three affected patients.

CONCLUSION

A DLK1 defect has been identified for the first time in a boy, underscoring the importance of genetic testing in males with idiopathic or sporadic CPP. The short stature reported by his untreated father suggests the need for timely diagnosis and treatment of subjects with DLK1 defects.

Aberrant Notch Signaling Pathway as a Potential Mechanism of Central Precocious Puberty

The Notch signaling pathway is highly conserved during evolution. It has been well documented that Notch signaling regulates cell proliferation, migration, and death in the nervous, cardiac, and endocrine systems. The Notch pathway is relatively simple, but its activity is regulated by numerous complex mechanisms. Ligands bind to Notch receptors, inducing their activation and cleavage. Various post-translational processes regulate Notch signaling by affecting the synthesis, secretion, activation, and degradation of Notch pathway-related proteins. Through such post-translational regulatory processes, Notch signaling has versatile effects in many tissues, including the hypothalamus. Recently, several studies have reported that mutations in genes related to the Notch signaling pathway were found in patients with central precocious puberty (CPP). CPP is characterized by the early activation of the hypothalamus–pituitary–gonadal (HPG) axis. Although genetic factors play an important role in CPP development, few associated genetic variants have been identified. Aberrant Notch signaling may be associated with abnormal pubertal development. In this review, we discuss the current knowledge about the role of the Notch signaling pathway in puberty and consider the potential mechanisms underlying CPP.

MKRN3 role in regulating pubertal onset: the state of art of functional studies

Puberty is a critical process characterized by several physical and psychological changes that culminate in the achievement of sexual maturation and fertility. The onset of puberty depends on several incompletely understood mechanisms that certainly involve gonadotropin-releasing hormone (GnRH) and its effects on the pituitary gland. The role of makorin ring finger protein 3 (MKRN3) in the regulation of pubertal timing was revealed when loss-of-function mutations were identified in patients with central precocious puberty (CPP), which to date, represent the most commonly known genetic cause of this condition. The MKRN3 gene showed ubiquitous expression in tissues from a broad spectrum of species, suggesting an important cellular role. Its involvement in the initiation of puberty and endocrine functions has just begun to be studied. This review discusses some of the recent approaches developed to predict MKRN3 functions and its involvement in pubertal development.

Genetic causes of central precocious puberty

Central precocious puberty (CPP) is a condition in which the hypothalamus–pituitary–gonadal system is activated earlier than the normal developmental stage. The etiology includes organic lesions in the brain; however, in the case of idiopathic diseases, environmental and/or genetic factors are involved in the development of CPP. A genetic abnormality in KISS1R, that encodes the kisspeptin receptor, was first reported in 2008 as a cause of idiopathic CPP. Furthermore, genetic alterations in KISS1, MKRN3, DLK1, and PROKR2 have been reported in idiopathic and/or familial CPP. Of these, MKRN3 has the highest frequency of pathological variants associated with CPP worldwide; but, abnormalities in MKRN3 are rare in patients in East Asia, including Japan. MKRN3 and DLK1 are maternal imprinting genes; thus, CPP develops when a pathological variant is inherited from the father. The mechanism of CPP due to defects in MKRN3 and DLK1 has not been completely clarified, but it is suggested that both may negatively control the progression of puberty. CPP due to such a single gene abnormality is extremely rare, but it is important to understand the mechanisms of puberty and reproduction. A further development in the genetics of CPP is expected in the future.

Central precocious puberty: Recent advances in understanding the aetiology and in the clinical approach

Central precocious puberty (CPP) results from early activation of the hypothalamic-pituitary-gonadal (HPG) axis. The current state of knowledge of the complex neural network acting at the level of the hypothalamus and the GnRH neuron to control puberty onset has expanded, particularly in the context of molecular interactions. Along with these advances, the knowledge of pubertal physiology and pathophysiology has also increased. This review focuses on regulatory abnormalities occurring at the hypothalamic level of the HPG axis to cause CPP. The clinical approach to diagnosis of puberty and pubertal disorders is also reviewed, with a particular focus on aetiologies of CPP. The recent identification of mutations in MKRN3 and DLK1 in familial as well sporadic forms of CPP has changed the state of the art of the approach to patients with CPP. Genetic advances have also had important repercussions beyond consideration of puberty alone. Syndromic disorders and central nervous system lesions associated with CPP are also discussed. If untreated, these conditions may lead to adverse physical, psychosocial and medical outcomes.

Diagnosis and management of precocious sexual maturation: an updated review

The classic definition of precocious sexual maturation is the development of secondary sexual characteristics before 8 years of age in girls and before 9 years of age in boys. It is classified as central precocious puberty when premature maturation of the hypothalamic-pituitary-gonadal axis occurs, and as peripheral precocious puberty when there is excessive secretion of sex hormones, independent of gonadotropin secretion. Precocious sexual maturation is more common in girls, generally central precocious puberty of idiopathic origin. In boys, it tends to be linked to central nervous system abnormalities. Clinical evaluation should include a detailed history and physical examination, including anthropometric measurements, calculation of growth velocity, and evaluation of secondary sexual characteristics. The main sign to suspect the onset of puberty is breast tissue development (thelarche) in girls and testicular enlargement (≥4 mL) in boys. Hormonal assessment and imaging are required for diagnosis and identification of the etiology. Genetic testing should be considered if there is a family history of precocious puberty or other clinical features suggestive of a genetic syndrome. Long-acting gonadotropin-releasing hormone analogs are the standard of care for central precocious puberty management, while peripheral precocious puberty management depends on the etiology.Conclusion: The aim of this review is to address the epidemiology, etiology, clinical assessment, and management of precocious sexual maturation. What is Known: • The main sign to suspect the onset of puberty is breast tissue development (thelarche) in girls and testicular enlargement (≥4 mL) in boys. The classic definition of precocious sexual maturation is the development of secondary sexual characteristics before 8 years of age in girls and before 9 years of age in boys. • Long-acting gonadotropin-releasing hormone agonist (GnRHa) is the standard of care for CPP management, and adequate hormone suppression results in the stabilization of pubertal progression, a decline in growth velocity, and a decrease in bone age advancement. What is New: • Most cases of precocious sexual maturation are gonadotropin-dependent and currently assumed to be idiopathic, but mutations in genes involved in pubertal development have been identified, such as MKRN3 and DLK1. • A different preparation of long-acting GnRHa is now available: 6-month subcutaneous injection.

Genetic etiologies of central precocious puberty

Pubertal onset is a complex process, which is influenced by genetic and environmental factors, such as obesity and endocrine-disrupting chemicals. In addition, the timing of normal puberty varies between individuals and is a highly polygenic trait with both rare and common variants. Central precocious puberty (CPP) is defined as the early activation of the hypothalamic-pituitary-gonadal axis. Genetic factors are suggested to account for 50% to 80% of the variation in puberty initiation, as indicated by the greater concordance of pubertal timing observed in monozygotic twins than in dizygotic twins. Although genetic factors play a crucial role in CPP development, only few associated genes have been identified. To date, four monogenic genes have been identified: KISS1, KISS1R, MKRN3, and DLK1. Moreover, mutation prevalence in these genes varies considerably depending on the ethnicity of patients with CPP. This article reviews the current knowledge on the normal pubertal timing and physiology and discusses the CPP-causing genes.

Pathogenic and Low-Frequency Variants in Children With Central Precocious Puberty

Background

Central precocious puberty (CPP) due to premature activation of GnRH secretion results in early epiphyseal fusion and to a significant compromise in the achieved final adult height. Currently, few genetic determinants of children with CPP have been described. In this translational study, rare sequence variants in MKRN3, DLK1, KISS1, and KISS1R genes were investigated in patients with CPP.

Methods

Fifty-four index girls and two index boys with CPP were first tested by Sanger sequencing for the MKRN3 gene. All children found negative (n = 44) for the MKRN3 gene were further investigated by whole exome sequencing (WES). In the latter analysis, the status of variants in genes known to be related with pubertal timing was compared with an in-house Cypriot control cohort (n = 43). The identified rare variants were initially examined by in silico computational algorithms and confirmed by Sanger sequencing. Additionally, a genetic network for the MKRN3 gene, mimicking a holistic regulatory depiction of the crosstalk between MKRN3 and other genes was designed.

Results

Three previously described pathogenic MKRN3 variants located in the coding region of the gene were identified in 12 index girls with CPP. The most prevalent pathogenic MKRN3 variant p.Gly312Asp was exclusively found among the Cypriot CPP cohort, indicating a founder effect phenomenon. Seven other CPP girls harbored rare likely pathogenic upstream variants in the MKRN3. Among the 44 CPP patients submitted to WES, nine rare DLK1 variants were identified in 11 girls, two rare KISS1 variants in six girls, and two rare MAGEL2 variants in five girls. Interestingly, the frequent variant rs10407968 (p.Gly8Ter) of the KISS1R gene appeared to be less frequent in the cohort of patients with CPP.

Conclusion

The results of the present study confirm the importance of the MKRN3-imprinted gene in genetics of CPP and its key role in pubertal timing. Overall, the results of the present study have emphasized the importance of an approach that aligns genetics and clinical aspects, which is necessary for the management and treatment of CPP.

Familial central precocious puberty: two novel MKRN3 mutations

BACKGROUND

Paternally inherited loss-of-function mutations in MKRN3 underlie central precocious puberty (CPP). We describe clinical and genetic features of CPP patients with paternally inherited MKRN3 mutations in two independent families.

METHODS

The single coding exon of MKRN3 was analyzed in three patients with CPP and their family members, followed by segregation analyses. Additionally, we report the patients' responses to GnRH analog treatment.

RESULTS

A paternally inherited novel heterozygous c.939C>G, p.(Ile313Met) missense mutation affecting the RING finger domain of MKRN3 was found in a Finnish girl with CPP (age at presentation 6 years). Two Polish siblings (a girl presenting with B2 at the age of 4 years and a boy with adult size testes at the age of 9 years) had inherited a novel heterozygous MKRN3 mutation c.1237_1252delGGAGACACATGCTTTT p.(Gly413Thrfs*63) from their father. The girls were treated with GnRH analogs, which exhibited suppression of the hypothalamic-pituitary-gonadal axis. In contrast, the male patient was not treated, yet he reached his target height.

CONCLUSIONS

We describe two novel MKRN3 mutations in three CPP patients. The first long-term data on a boy with CPP due to an MKRN3 mutation questions the role of GnRH analog treatment in augmenting adult height in males with this condition.

IMPACT

We describe the genetic cause for central precocious puberty (CPP) in two families. This report adds two novel MKRN3 mutations to the existing literature. One of the mutations, p.(Ile313Met) affects the RING finger domain of MKRN3, which has been shown to be important for repressing the promoter activity of KISS1 and TAC3. We describe the first long-term observation of a male patient with CPP due to a paternally inherited MKRN3 loss-of-function mutation. Without GnRH analog treatment, he achieved an adult height that was in accordance with his mid-parental target height.

Central nervous system imaging in girls with central precocious puberty: when is necessary?

Objective

The determinants of an increased risk of an organic pathology underlying central precocious puberty (CPP) in girls remain contentious. The present study aimed to determine the clinical and hormonal findings that can be used to differentiate organic and idiopathic CPP in girls as a screening method so that only those considered likely to have organic CPP undergo cranial magnetic resonance imaging (MRI).

Methods

The medical records of 286 girls that received GnRH agonist (GnRHa) therapy for CPP were retrospectively evaluated. Chronological and bone age, height, pubertal stage, and basal/stimulated gonadotropin and estradiol (E₂) levels, as well as cranial MRI findings at the time CPP was diagnosed were recorded. Clinical and hormonal parameters that can be used to differentiate between girls with organic and idiopathic CPP were identified using ROC curves.

Results

Organic CPP was noted in 6.3% of the participants. Puberty started before age 6 years in 88.9% of the girls with organic CPP. Mean E₂ and peak luteinizing hormone (LH) levels were higher in the girls with organic CPP than in those with idiopathic CPP that were matched for pubertal stage, as follows: early stage puberty (Tanner 2 and 3): E₂: 62.4 ± 19.8 pg/mL vs. 29.1 ± 9.5 pg/mL; peak LH: 16.8 ± 3.2 IU/L vs. 12.2 ± 3.7 IU/L; advanced stage puberty (Tanner 4): mean E₂: 87.6 ± 3.4 pg/mL vs. 64.6 ± 21.2 pg/mL; peak LH: 20.8 ± 0.4 IU/L vs. 16.6 ± 5.8 IU/L (P < 0.001 for all). Thresholds for differentiating organic and idiopathic CPP in girls with early-stage puberty were 38.1 pg/mL for E₂ (100% sensitivity and 80.4% specificity) and 13.6 IU/L for peak LH (100% sensitivity and 66.4% specificity).

Conclusion

Pubertal symptoms and signs generally begin before age 6 years and hormone levels are much higher than expected for pubertal stage in girls with organic CPP. Based on the present findings, cranial MRI is recommended for girls aged < 6 years, as the risk of diagnosing an organic pathology is highest in this age group. Hormone levels higher than expected for pubertal stage might be another indication for cranial MRI, regardless of patient age. Cranial MRI should be performed in girls with early-stage puberty, and an E₂ level > 38 pg/mL and/or a peak LH level > 13.6 IU/L.

Genotype-Phenotype Correlations in Central Precocious Puberty Caused by MKRN3 Mutations

CONTEXT

Loss-of-function mutations of makorin RING finger protein 3 (MKRN3) are the most common monogenic cause of familial central precocious puberty (CPP).

OBJECTIVE

To describe the clinical and hormonal features of a large cohort of patients with CPP due to MKRN3 mutations and compare the characteristics of different types of genetic defects.

METHODS

Multiethnic cohort of 716 patients with familial or idiopathic CPP screened for MKRN3 mutations using Sanger sequencing. A group of 156 Brazilian girls with idiopathic CPP (ICPP) was used as control group.

RESULTS

Seventy-one patients (45 girls and 26 boys from 36 families) had 18 different loss-of-function MKRN3 mutations. Eight mutations were classified as severe (70% of patients). Among the 71 patients, first pubertal signs occurred at 6.2 ± 1.2 years in girls and 7.1 ± 1.5 years in boys. Girls with MKRN3 mutations had a shorter delay between puberty onset and first evaluation and higher follicle-stimulating hormone levels than ICPP. Patients with severe MKRN3 mutations had a greater bone age advancement than patients with missense mutations (2.3 ± 1.6 vs 1.6 ± 1.4 years, P = .048), and had higher basal luteinizing hormone levels (2.2 ± 1.8 vs 1.1 ± 1.1 UI/L, P = .018) at the time of presentation. Computational protein modeling revealed that 60% of the missense mutations were predicted to cause protein destabilization.

CONCLUSION

Inherited premature activation of the reproductive axis caused by loss-of-function mutations of MKRN3 is clinically indistinct from ICPP. However, the type of genetic defect may affect bone age maturation and gonadotropin levels.

Central Precocious Puberty in Boys and Girls: Similarities and Differences

Central precocious puberty (CPP) is due to the premature activation of the hypothalamic–pituitary–gonadal axis, which is responsible for the appearance of secondary sexual characteristics. It occurs before the age of 8 and 9 in girls and boys, respectively. CPP shows higher incidence in females than in males. Causes of CPP are similar in both sexes, but the idiopathic form is more frequent in girls, while organic forms are more frequent in males. Recent studies demonstrated a role of some genetic variants in the pathogenesis of CPP. The diagnostic evaluation based on accurate physical examination, assessment of the pituitary–gonadal axis, pelvic sonography in girls, and determination of bone age. Magnetic resonance of the central nervous system should be done in all boys and selected girls. Since the 1980s, pharmacologic treatment involves the use of gonadotropin-releasing hormone (GnRH) analogs. These drugs are characterized by few side effects and long-term safety. Many data are available on the outcome of GnRH analog treated female patients, while poor data are reported in boys. Adult height is improved in both sexes.

Makorin RING finger protein 3 and central precocious puberty

Makorin RING finger protein 3 (MKRN3) is a key inhibitor of the hypothalamic-pituitary-gonadal axis. Loss-of-function mutations in MKRN3 cause familial and sporadic central precocious puberty (CPP), while polymorphisms are associated with age at menarche. To date, 115 patients with CPP carrying MKRN3 mutations have been described, harboring 48 different genetic variants. The prevalence of MKRN3 mutations in genetically screened populations with CPP is estimated at 9.0%. Girls are more commonly and more seriously affected than boys. MKRN3 is expressed in humans and rodents in the central nervous system. Circulating levels in humans and hypothalamic expression in rodents decrease during pubertal progression. Although some MKRN3 regulators have been identified, the precise mechanism by which MKRN3 inhibits the hypothalamic-pituitary-gonadal axis remains elusive. The role of makorins in developmental physiology and organ differentiation and the role of maternal imprinting are discussed herein.

GENETICS IN ENDOCRINOLOGY: Genetic etiologies of central precocious puberty and the role of imprinted genes

Pubertal timing is regulated by the complex interplay of genetic, environmental, nutritional and epigenetic factors. Criteria for determining normal pubertal timing, and thus the definition of precocious puberty, have evolved based on published population studies. The significance of the genetic influence on pubertal timing is supported by familial pubertal timing and twin studies. In contrast to the many monogenic causes associated with hypogonadotropic hypogonadism, only four monogenic causes of central precocious puberty (CPP) have been described. Loss-of-function mutations in Makorin Ring Finger Protein 3(MKRN3), a maternally imprinted gene on chromosome 15 within the Prader-Willi syndrome locus, are the most common identified genetic cause of CPP. More recently, several mutations in a second maternally imprinted gene, Delta-like noncanonical Notch ligand 1 (DLK1), have also been associated with CPP. Polymorphisms in both genes have also been associated with the age of menarche in genome-wide association studies. Mutations in the genes encoding kisspeptin (KISS1) and its receptor (KISS1R), potent activators of GnRH secretion, have also been described in association with CPP, but remain rare monogenic causes. CPP has both short- and long-term health implications for children, highlighting the importance of understanding the mechanisms contributing to early puberty. Additionally, given the role of mutations in the imprinted genes MKRN3 and DLK1 in pubertal timing, other imprinted candidate genes should be considered for a role in puberty initiation.

A novel heterozygous MKRN3 nonsense mutation in a Chinese girl with idiopathic central precocious puberty: A case report

RATIONALE

Central precocious puberty (CPP) is caused by the premature activation of the hypothalamic-pituitary-gonadal axis. Recently, the makorin ring finger protein 3 (MKRN3) mutations represent the most common genetic defects associated with CPP. However, the MKRN3 mutation is relatively rare in Asian countries. Here, we identified a novel heterozygous MKRN3 nonsense mutation (p. Gln363) causing CPP in a Chinese girl.

PATIENT CONCERNS

The index case is a 7-year-old Chinese girl who presented rapidly progressive precocious puberty with the onset of menstrual period 2 months after breast development, the advanced bone age (11 years), and the accelerated growth velocity (10 cm/year). Her basal luteinizing hormone (LH) and follicle-stimulating hormone (FSH) levels, as well as the peak LH/FSH values after the gonadotropin-releasing hormone (GnRH) stimulation test were significantly elevated.Pelvic B ultrasound showed the presence of ovarian follicles with diameters ≥0.4 cm. Uterine length also indicated the onset of puberty. Contrast-enhanced magnetic resonance imaging (MRI) did not disclose any abnormality in the pituitary. Additionally, our present case was obese companies with impaired glucose tolerance (IGT) at the baseline assessment. Genetic analysis revealed a novel heterozygous nonsense mutation (c1087C>T; p. Gln363) in the maternally imprinted MKRN3, which inherited from the girl's father.

DIAGNOSIS

Combined with the symptoms, hormonal data, and the results of the pelvic B ultrasound, the girl was diagnosed as CPP.

INTERVENTIONS

The girl has been treated with a GnRH analog (3.75 mg every 4 wks) for 1 year and 5 months.

OUTCOMES

The puberty signs have since not progressed during the follow-up period, which indicates that the GnRH analogs treatment is effective.

LESSONS

This case was obese companied with IGT at the baseline assessment and exhibited stronger LH/FSH response to GnRH stimulation test. Therefore, clinicians should highlight the importance of weight management and the long-term follow-up to monitor the adverse health outcomes, especially for the polycystic ovary syndrome in later life.

Unravelling the role of epigenetics in reproductive adaptations to early-life environment

Reproductive function adjusts in response to environmental conditions in order to optimize success. In humans, this plasticity includes age of pubertal onset, hormone levels and age at menopause. These reproductive characteristics vary across populations with distinct lifestyles and following specific childhood events, and point to a role for the early-life environment in shaping adult reproductive trajectories. Epigenetic mechanisms respond to external signals, exert long-term effects on gene expression and have been shown in animal and cellular studies to regulate normal reproductive function, strongly implicating their role in these adaptations. Moreover, human cohort data have revealed differential DNA methylation signatures in proxy tissues that are associated with reproductive phenotypic variation, although the cause-effect relationships are difficult to discern, calling for additional complementary approaches to establish functionality. In this Review, we summarize how adult reproductive function can be shaped by childhood events. We discuss why the influence of the childhood environment on adult reproductive function is an important consideration in understanding how reproduction is regulated and necessitates consideration by clinicians treating women with diverse life histories. The resolution of the molecular mechanisms responsible for human reproductive plasticity could also lead to new approaches for intervention by targeting these epigenetic modifications.

Precocious puberty

Precocious puberty (PP) is a common reason for referral to pediatric endocrinology clinics, with a strong female predominance. PP is a broad term encompassing benign variants of normal development, gonadotropin-dependent precious puberty (GDPP), and gonadotropin-independent precocious puberty (GIPP). This article reviews the definitions, physiology, clinical presentation, evaluation and treatment of these conditions.

Makorin rings the kisspeptin bell to signal pubertal initiation

The signals maintaining quiescence of the reproductive endocrine axis during childhood before its reawakening at puberty had been enigmatic. Studies in patients with abnormal puberty have illuminated the identity of the signals; kisspeptin has emerged as a major stimulator of puberty, and makorin RING finger protein 3 (MKRN3) as an inhibitory signal that prevents premature initiation of puberty. In this issue of the JCI, Abreu et al. investigated the mechanism by which MKRN3 regulates pubertal onset. The authors found that a reduction in MKRN3 alleviated the constraint on kisspeptin-expressing neurons to allow pubertal initiation, a phenomenon observed across species, including nonhuman primates. Further, the ubiquitinase activity of MKRN3 required its RING finger domain, in order to repress the promoter activity of genes encoding kisspeptin and neurokinin B. These data advance our understanding of the regulation of kisspeptin-expressing neurons by MKRN3 to initiate puberty.

Heterozygous Deletions in MKRN3 Cause Central Precocious Puberty Without Prader-Willi Syndrome

CONTEXT

Loss-of-function mutations in the imprinted genes MKRN3 and DLK1 cause central precocious puberty (CPP) but whole gene deletions have not been reported. Larger deletions of the chromosome 15q11-13 imprinted locus, including MKRN3, cause Prader-Willi syndrome (PWS). CPP has been reported in PWS but is not common, and the role of MKRN3 in PWS has not been fully elucidated.

OBJECTIVE

To identify copy number variants in puberty-related, imprinted genes to determine their role in CPP.

METHODS

Probands with idiopathic CPP had chromosomal microarray (CMA) and targeted deletion/duplication testing for MKRN3 and DLK1.

RESULTS

Sixteen female probands without MKRN3 or DLK1 variants identified by Sanger sequencing were studied. Whole gene deletions of MKRN3 were identified in 2 subjects (13%): a complete deletion of MKRN3 in Patient A (pubertal onset at 7 years) and a larger deletion involving MAGEL2, MKRN3, and NDN in Patient B (pubertal onset 5.5 years). Both were paternally inherited. Patient B had no typical features of PWS, other than obesity, which was also present in her unaffected family.

CONCLUSIONS

We identified 2 cases of whole gene deletions of MKRN3 causing isolated CPP without PWS. This is the first report of complete deletions of MKRN3 in patients with CPP, emphasizing the importance of including copy number variant analysis for MKRN3 mutation testing when a genetic diagnosis is suspected. We speculate that there is a critical region of the PWS locus beyond MKRN3, MAGEL2, and NDN that is responsible for the PWS phenotype.

Syndromic Disorders Caused by Disturbed Human Imprinting

Imprinting disorders are a group of congenital diseases caused by dysregulation of genomic imprinting, affecting prenatal and postnatal growth, neurocognitive development, metabolism and cancer predisposition. Aberrant expression of imprinted genes can be achieved through different mechanisms, classified into epigenetic - if not involving DNA sequence change - or genetic in the case of altered genomic sequence. Despite the underlying mechanism, the phenotype depends on the parental allele affected and opposite phenotypes may result depending on the involvement of the maternal or the paternal chromosome. Imprinting disorders are largely underdiagnosed because of the broad range of clinical signs, the overlap of presentation among different disorders, the presence of mild phenotypes, the mitigation of the phenotype with age and the limited availability of molecular techniques employed for diagnosis. This review briefly illustrates the currently known human imprinting disorders, highlighting endocrinological aspects of pediatric interest.

Evaluation of Serum Makorin Ring Finger Protein 3 (MKRN3) Levels in Girls With Idiopathic Central Precocious Puberty and Premature Thelarche

This study aims to investigate serum makorin ring finger protein 3 (MKRN3) levels in girls with idiopathic central precocious puberty (ICPP) and premature thelarche (PT), in order to determine whether circulating MKRN3 level is associated with ICPP and PT. A total of 90 girls were enrolled in the study. 30 age-matched girls were allocated for each group (ICPP, PT and healthy controls [HC], respectively). The base LH (B-LH) and E2 levels were higher in ICPP girls than those in HC and PT girls. The peak LH (P-LH) levels and P-LH/P-FSH values were obviously higher in ICPP girls than those in PT girls, while higher peak FSH (P-FSH) levels were detected in PT girls when compared to those in ICPP girls. Kisspeptin levels were lower in HC girls than those in ICPP and PT girls. MKRN3 levels were the highest in HC girls among the three groups. There were relatively strong negative correlations among MKRN3, kisspeptin and P-LH/P-FSH. Circulating MKRN3 can have an important role in the onset of ICPP and PT. However, this should not be used as an independent diagnostic criterion for diagnosing ICPP or differentiating ICPP from PT, but should be used only as an adjunctive diagnostic biomarker.

MKRN3 regulates the epigenetic switch of mammalian puberty via ubiquitination of MBD3

Central precocious puberty (CPP) refers to a human syndrome of early puberty initiation with characteristic increase in hypothalamic production and release of gonadotropin-releasing hormone (GnRH). Previously, loss-of-function mutations in human MKRN3, encoding a putative E3 ubiquitin ligase, were found to contribute to about 30% of cases of familial CPP. MKRN3 was thereby suggested to serve as a ‘brake’ of mammalian puberty onset, but the underlying mechanisms remain as yet unknown. Here, we report that genetic ablation of Mkrn3 did accelerate mouse puberty onset with increased production of hypothalamic GnRH1. MKRN3 interacts with and ubiquitinates MBD3, which epigenetically silences GNRH1 through disrupting the MBD3 binding to the GNRH1 promoter and recruitment of DNA demethylase TET2. Our findings have thus delineated a molecular mechanism through which the MKRN3–MBD3 axis controls the epigenetic switch in the onset of mammalian puberty.

Outcomes of Patients with Central Precocious Puberty Due to Loss-of-Function Mutations in the MKRN3 Gene after Treatment with Gonadotropin-Releasing Hormone Analog

INTRODUCTION

Loss-of-function mutation of MKRN3 represents the most frequent genetic cause of familial central precocious puberty (CPP). The outcomes of gonadotropin-releasing hormone analog (GnRHa) treatment in CPP patients with MKRN3 defects are unknown.

OBJECTIVE

To describe the clinical and hormonal features of patients with CPP with or without MKRN3 mutations after GnRHa treatment. Anthropometric, metabolic and reproductive parameters were evaluated.

PATIENTS AND METHODS

Twenty-nine female patients with CPP due to loss-of-function mutations in the MKRN3 and 43 female patients with idiopathic CPP were included. Their medical records were retrospectively evaluated for clinical, laboratory, and imaging study, before, during, and after GnRHa treatment. All patients with idiopathic CPP and 11 patients with CPP due to MKRN3 defects reached final height (FH).

RESULTS

At the diagnosis, there were no significant differences between clinical and laboratory features of patients with CPP with or without MKRN3 mutations. A high prevalence of overweight and obesity was observed in patients with CPP with or without MKRN3 mutations (47.3 and 50%, respectively), followed by a significant reduction after GnRHa treatment. No significant differences in the values of mean FH and target height were found between the 2 CPP groups after GnRHa treatment. Menarche occurred at the expected age in patients with or without CPP due to MKRN3 mutations (11.5 ± 1.3 and 12 ± 0.6 years, respectively). The prevalence of polycystic ovarian syndrome was 9.1% in patients with CPP due to MKRN3 mutations and 5.9% in those with idiopathic CPP.

CONCLUSION

Anthropometric, metabolic, and reproductive outcomes after GnRHa treatment were comparable in CPP patients, with or without MKRN3 mutations, suggesting the absence of deleterious effects of MKRN3 defects in young female adults' life.

Hypothalamic miR-30 regulates puberty onset via repression of the puberty-suppressing factor, Mkrn3

Mkrn3, the maternally imprinted gene encoding the makorin RING-finger protein-3, has recently emerged as putative pubertal repressor, as evidenced by central precocity caused by MKRN3 mutations in humans; yet, the molecular underpinnings of this key regulatory action remain largely unexplored. We report herein that the microRNA, miR-30, with three binding sites in a highly conserved region of its 3' UTR, operates as repressor of Mkrn3 to control pubertal onset. Hypothalamic miR-30b expression increased, while Mkrn3 mRNA and protein content decreased, during rat postnatal maturation. Neonatal estrogen exposure, causing pubertal alterations, enhanced hypothalamic Mkrn3 and suppressed miR-30b expression in female rats. Functional in vitro analyses demonstrated a strong repressive action of miR-30b on Mkrn3 3' UTR. Moreover, central infusion during the juvenile period of target site blockers, tailored to prevent miR-30 binding to Mkrn3 3' UTR, reversed the prepubertal down-regulation of hypothalamic Mkrn3 protein and delayed female puberty. Collectively, our data unveil a novel hypothalamic miRNA pathway, involving miR-30, with a prominent role in the control of puberty via Mkrn3 repression. These findings expand our current understanding of the molecular basis of puberty and its disease states.

Pioneering studies on monogenic central precocious puberty

Pubertal timing in humans is determined by complex interactions including hormonal, metabolic, environmental, ethnic, and genetic factors. Central precocious puberty (CPP) is defined as the premature reactivation of the hypothalamic-pituitary-gonadal axis, starting before the ages of 8 and 9 years in girls and boys, respectively; familial CPP is defined by the occurrence of CPP in two or more family members. Pioneering studies have evidenced the participation of genetic factors in pubertal timing, mainly identifying genetic causes of CPP in sporadic and familial cases. In this context, rare activating mutations were identified in genes of the kisspeptin excitatory pathway (KISS1R and KISS1 mutations). More recently, loss-of-function mutations in two imprinted genes (MKRN3 and DLK1) have been identified as important causes of familial CPP, describing novel players in the modulation of the hypothalamic-pituitary-gonadal axis in physiological and pathological conditions. MKRN3 mutations are the most common cause of familial CPP, and patients with MKRN3 mutations present clinical features indistinguishable from idiopathic CPP. Meanwhile, adult patients with DLK1 mutations present high frequency of metabolic alterations (overweight/obesity, early onset type 2 diabetes and hyperlipidemia), indicating that DLK1 may be a novel link between reproduction and metabolism. Arch Endocrinol Metab. 2019;63(4):438-44.

Evolutionary Conservation of MKRN3 and Other Makorins and Their Roles in Puberty Initiation and Endocrine Functions

Puberty is a critical period of development regulated by genetic, nutritional, and environmental factors. The role of makorin ring finger protein 3 (MKRN3) in the regulation of pubertal timing was revealed when loss-of-function mutations were identified in patients with central precocious puberty (CPP). To date, MKRN3 mutations are the most common known genetic cause of CPP. MKRN3 is a member of the makorin family of ubiquitin ligases, together with MKRN1 and MKRN2. The Mkrn genes have been identified in both vertebrates and invertebrates and show high evolutionary conservation of their gene and protein structures. While the existence of Mkrn orthologues in a wide spectrum of species suggests a vital cellular role of the makorins, their role in puberty initiation and endocrine functions is just beginning to be investigated. In this review, we discuss recent studies that have shown the involvement of Mkrn3 and other makorins in the regulation of pubertal development and other endocrine functions, including metabolism and fertility, as well as their underlying mechanisms of action.

Central precocious puberty, functional and tumor-related

Precocious puberty is defined as the appearance of secondary sex characteristics before 8 years of age in girls and before 9 years of age in boys. Central precocious puberty (CPP) is diagnosed when activation of the hypothalamic-pituitary axis is identified. It is a rare disease with a clear female predominance. A background of international adoption increases its risk, with other environmental factors such as endocrine disruptors also being associated with CPP. The causes of CPP are heterogeneous, with alterations of the CNS being of special interest. Physical injuries of the CNS are more frequent in boys, while idiopathic etiology is more prevalent among girls. However, in the last decade the number of idiopathic cases has diminished thanks to the discovery of mutations in different genes, including KISS1, KISS1R, MKRN3, and DLK1 that cause CPP. For the diagnosis of CPP, hormone studies are needed in addition to the clinical data regarding signs of pubertal onset. For this purpose, the GnRH test continues to be the gold standard. Imaging analyses, such as bone age and brain MRI, are also very useful. Furthermore, genetic testing must be incorporated in the diagnosis of CPP, especially in familial cases. Early puberty has been related to various consequences in the medium and long term such as behavioral problems, breast cancer, obesity, and metabolic comorbidities. However, there are few studies that have exclusively analyzed patients with CPP. GnRH analogs are the most frequent treatment election with the main objective being to improve adult height. Currently, there are new formulations that are being investigated.

MKRN3 Mutations in Central Precocious Puberty: A Systematic Review and Meta-Analysis

MKRN3 mutations represent the most common genetic cause of central precocious puberty (CPP) but associations between genotype and clinical features have not been extensively explored. This systematic review and meta-analysis investigated genotype-phenotype associations and prevalence of MKRN3 mutations in CPP. The search was conducted in seven electronic databases (Cochrane, EMBASE, LILACS, LIVIVO, PubMed, Scopus, and Web of Science) for articles published until 4 September 2018. Studies evaluating MKRN3 mutations in patients with CPP were considered eligible. A total of 22 studies, studying 880 subjects with CPP, fulfilled the inclusion criteria. Eighty-nine subjects (76 girls) were identified as harboring MKRN3 mutations. Girls, compared with boys, exhibited earlier age at pubertal onset (median, 6.0 years; range, 3.0 to 7.0 vs 8.5 years; range, 5.9 to 9.0; P < 0.001), and higher basal FSH levels (median, 4.3 IU/L; range, 0.7 to 13.94 IU/L vs 2.45 IU/L; range, 0.8 to 13.70 IU/L; P = 0.003), and bone age advancement (ΔBA; median, 2.3 years; range, -0.9 to 5.2 vs 1.2 years; range, 0.0 to 2.3; P = 0.01). Additional dysmorphisms were uncommon. A total of 14 studies evaluating 857 patients were included for quantitative analysis, with a pooled overall mutation prevalence of 9.0% (95% CI, 0.04 to 0.15). Subgroup analysis showed that prevalence estimates were higher in males, familial cases, and in non-Asian countries. In conclusion, MKRN3 mutations are associated with nonsyndromic CPP and manifest in a sex-dimorphic manner, with girls being affected earlier. They represent a common cause of CPP in western countries, especially in boys and familial cases.

MKRN3 Levels in Girls with Central Precocious Puberty during GnRHa Treatment: A Longitudinal Study

BACKGROUND

Recently, mutations of makorin RING finger protein 3 (MKRN3) have been identified in familial central precocious puberty (CPP). Serum levels of this protein decline before the pubertal onset in healthy girls and boys and are lower in patients with CPP compared to prepubertal matched pairs. The aim of our study was to investigate longitudinal changes in circulating MKRN3 levels in patients with CPP before and during GnRH analogs (GnRHa) treatment.

METHODS

We performed a longitudinal prospective study. We enrolled 15 patients with CPP aged 7.2 years (range: 2-8) with age at breast development onset < 8 years and 12 control girls matched for the time from puberty onset (mean age 11.8 ± 1.2 years). Serum values of MKRN3, gonadotropins, and 17β-estradiol were evaluated before and during treatment with GnRHa (at 6 and 12 months). The MKRN3 gene was genotyped in CPP patients. In the girls from the control group, only basal levels were analyzed.

RESULTS

No MKRN3 mutations were found among CPP patients. MKRN3 levels declined significantly from baseline to 6 months of GnRHa treatment (p = 0.0007) and from 6 to 12 months of treatment (p = 0.003); MKRN3 levels at 6 months were significantly lower than in the control girls (p < 0.0001).

CONCLUSIONS

We showed that girls with CPP had a decline in peripheral levels of MKRN3 during GnRHa treatment. Our data suggest a suppression of MKRN3 by continuous pharmacological administration of GnRHa.

(Epi)genetic defects of MKRN3 are rare in Asian patients with central precocious puberty

We sequenced MKRN3, the major causative gene of central precocious puberty in Western countries, in 24 Japanese or Chinese patients and examined the DNA methylation and copy-number statuses of this gene in 19 patients. We identified no (epi)genetic defects except for one previously reported mutation. These results, together with reports from Korea, indicate that MKRN3 defects are rare in Asian populations. The ethnic differences likely reflect Western country-specific founder mutations and the rarity of de novo mutations.

The Emerging Role of Chromatin Remodeling Factors in Female Pubertal Development

To attain sexual competence, all mammalian species go through puberty, a maturational period during which body growth and development of secondary sexual characteristics occur. Puberty begins when the diurnal pulsatile gonadotropin-releasing hormone (GnRH) release from the hypothalamus increases for a prolonged period of time, driving the adenohypophysis to increase the pulsatile release of luteinizing hormone with diurnal periodicity. Increased pubertal GnRH secretion does not appear to be driven by inherent changes in GnRH neuronal activity; rather, it is induced by changes in transsynaptic and glial inputs to GnRH neurons. We now know that these changes involve a reduction in inhibitory transsynaptic inputs combined with increased transsynaptic and glial excitatory inputs to the GnRH neuronal network. Although the pubertal process is known to have a strong genetic component, during the last several years, epigenetics has been implicated as a significant regulatory mechanism through which GnRH release is first repressed before puberty and is involved later on during the increase in GnRH secretion that brings about the pubertal process. According to this concept, a central target of epigenetic regulation is the transcriptional machinery of neurons implicated in stimulating GnRH release. Here, we will briefly review the hormonal changes associated with the advent of female puberty and the role that excitatory transsynaptic inputs have in this process. In addition, we will examine the 3 major groups of epigenetic modifying enzymes expressed in the neuroendocrine hypothalamus, which was recently shown to be involved in pubertal development and progression.

MKRN3 Interacts With Several Proteins Implicated in Puberty Timing but Does Not Influence GNRH1 Expression

Paternally-inherited loss-of-function mutations in makorin ring finger protein 3 gene (MKRN3) underlie central precocious puberty. To investigate the puberty-related mechanism(s) of MKRN3 in humans, we generated two distinct bi-allelic MKRN3 knock-out human pluripotent stem cell lines, Del 1 and Del 2, and differentiated them into GNRH1-expressing neurons. Both Del 1 and Del 2 clones could be differentiated into neuronal progenitors and GNRH1-expressing neurons, however, the relative expression of GNRH1 did not differ from wild type cells (P = NS). Subsequently, we investigated stable and dynamic protein-protein interaction (PPI) partners of MKRN3 by stably expressing it in HEK cells followed by mass spectrometry analyses. We found 81 high-confidence novel protein interaction partners, which are implicated in cellular processes such as insulin signaling, RNA metabolism and cell-cell adhesion. Of the identified interactors, 20 have been previously implicated in puberty timing. In conclusion, our stem cell model for generation of GNRH1-expressing neurons did not offer mechanistic insight for the role of MKRN3 in puberty initiation. The PPI data, however, indicate that MKRN3 may regulate puberty by interacting with other puberty-related proteins. Further studies are required to elucidate the possible mechanisms and outcomes of these interactions.

Low Frequency of MKRN3 and DLK1 Variants in Chinese Children with Central Precocious Puberty

BACKGROUND

Central precocious puberty (CPP) is defined by gonadotropin-dependent development of secondary sexual characteristics before the age of 8 years in girls and 9 years in boys. MKRN3 and DLK1 are two genes, disease-causing variants of which have recently been discovered to cause idiopathic CPP.

METHODS

We screened 173 Chinese patients (9 males and 164 females; 9 familial and 164 sporadic) with ICPP and 43 patients (9 males and 34 females; 3 familial and 40 sporadic) with early puberty for variants in MKRN3. We also screened 19 patients with ICPP and early puberty for variants of DLK1 (17 males and 2 females; 5 familial and 14 sporadic).

RESULTS

We identified four novel missense variants of MKRN3, c.1138G > A (p.Glu380Lys), c.1420T > A (p.Leu474Met), c.673C > G (p.Leu225Val), and c.1071C > G (p.Ile357Met) in two sporadic cases and three familial cases. According to ACMG standards, two MKRN3 variant (p.Glu380Lys and p.Ile357Met) are likely pathogenic, and two others are of uncertain significance. We also performed bioinformatic analysis to evaluate the impact of variants on MKRN3 protein structures, which showed that Ile357Met locates at the zinc-binding region (C3HC4 RING finger motif), while Glu380Lys is spatially extremely close to the C3HC4 RING finger, MKRN-specific Cys-His domain, and the third C3H1 zinc-finger motif region. Per Glu380Lys, Glu with negative charges has been changed into Lys with positive charges, which may affect the hydrogen bond formation between amino acids and the stability of the local structure, thus affecting the binding of zinc iron to MKRN3 protein. Besides, we did not identify any variants of DLK1 gene in our patients.

CONCLUSIONS

In this study, we report four novel MKRN3 variants in patients with ICPP. Moreover, we did not find any variants of DLK1 gene. Variants of MKRN3 are relatively uncommon in Chinese ICPP patients.

GENETICS IN ENDOCRINOLOGY: Genetic diagnosis of endocrine diseases by NGS: novel scenarios and unpredictable results and risks

The technological advancements in genetics produced a profound impact on the research and diagnostics of non-communicable diseases. The availability of next-generation sequencing (NGS) allowed the identification of novel candidate genes but also an in-depth modification of the understanding of the architecture of several endocrine diseases. Several different NGS approaches are available allowing the sequencing of several regions of interest or the whole exome or genome (WGS, WES or targeted NGS), with highly variable costs, potentials and limitations that should be clearly known before designing the experiment. Here, we illustrate the NGS scenario, describe the advantages and limitations of the different protocols and review some of the NGS results obtained in different endocrine conditions. We finally give insights on the terminology and requirements for the implementation of NGS in research and diagnostic labs.

Investigation of MKRN3 Mutation in Patients with Familial Central Precocious Puberty

OBJECTIVE

There have been recent advances in the understanding of the etiology of idiopathic central precocious puberty (iCPP) including new genetic associations. The aim of this clinical study was to determine the frequency of MKRN3 mutation in cases of familial iCPP.

METHODS

Potential sequence variations in the maternally imprinted MKRN3 gene were evaluated in 19 participants from 10 families using next-generation sequencing analysis.

RESULTS

MKRN3 variation was found in only one of the 19 (5.3%) subjects. The male patient, who had a medical history of precocious puberty, had a heterozygous mutation, NM_005664.3:c.630_650delins GCTGGGC (p.P211Lfs*16). The father of this patient also had a history of precocious puberty and had the same mutation. p.P211Lfs*16 is a novel variant and it was identified as probably pathogenic by in silico analysis, consistent with the clinical findings.

CONCLUSION

Given that MKRN3 mutation was detected in only one patient, with a paternal history of precocious puberty, this reinforces the importance of accurate family history taking. The detected incidence of MKRN3 variants in our case series was much lower than reported elsewhere which suggests a need for further studies in Turkish iCPP patients.

Genetics of pubertal timing

PURPOSE OF REVIEW

To summarize advances in the genetics underlying variation in normal pubertal timing, precocious puberty, and delayed puberty, and to discuss mechanisms by which genes may regulate pubertal timing.

RECENT FINDINGS

Genome-wide association studies have identified hundreds of loci that affect pubertal timing in the general population in both sexes and across ethnic groups. Single genes have been implicated in both precocious and delayed puberty. Potential mechanisms for how these genetic loci influence pubertal timing may include effects on the development and function of the GnRH neuronal network and the responsiveness of end-organs.

SUMMARY

There has been significant progress in identifying genetic loci that affect normal pubertal timing, and the first single-gene causes of precocious and delayed puberty are being described. How these genes influence pubertal timing remains to be determined.

Central precocious puberty: From genetics to treatment

Central precocious puberty (CPP) results from early activation of the hypothalamic - pituitary -gonadal (HPG) axis and follows the same sequence as normal puberty. While many factors involved in pubertal initiation remain poorly understood, the kisspeptin system is known to play a key role. Currently, mutations in the kisspeptin system, MKRN3, and DLK1 have been identified in sporadic and familial cases of CPP. The diagnosis is based on physical exam findings indicating advancing puberty and on laboratory tests confirming central HPG axis activation. GnRH analogs are the mainstay of treatment and are used with the goal of height preservation. Newer extended release formulations continue to be developed. Currently there is no evidence of long-term complications associated with treatment. However, many areas remain to be explored such as targeted therapies and aspects of clinical management. Further investigation into psychological effects and additional data regarding long-term outcomes, particularly in males, is needed.

Association between MKRN3 and LIN28B polymorphisms and precocious puberty

BACKGROUND

The present study aimed to investigate the association between MKRN3 and LIN28B gene polymorphisms and precocious puberty in Korean boys and girls.

RESULTS

Children 7 to 9 years of age in 2011 to 2012 who were part of the Ewha Birth & Growth Cohort Study were recruited for this study. A total of 103 girls and 70 boys were included in the analyses. Seven girls and 26 boys were identified to have precocious puberty. Among four single nucleotide polymorphisms (SNPs) of MKRN3 and two SNPs of LIN28B examined, three SNPs (rs2239669, rs6576457, and rs12441827) showed significant associations with precocious puberty in additive models in boys but no significance was found in any SNPs in girls. From the logistic regression analysis, boys with TT alleles in rs12441827 had about a four-times greater risk for precocious puberty when compared to C allele carriers (OR = 3.95, 95% CI = 1.27-12.32 in model 1). eQTL analysis revealed that SNPs of statistical significance from our study did not show the variation in expression profiles nor found in the database.

CONCLUSIONS

This study supports the impact of MKRN3 SNP rs12441827 on precocious puberty in Korean boys. The results add a further aspect to genetic association in precocious puberty along with complex interactions of environmental, nutritional and socioeconomic factors.

Hypothalamic epigenetics driving female puberty

Puberty involves a series of morphological, physiological and behavioural changes during the last part of the juvenile period that culminates in the attainment of fertility. The activation of the pituitary-gonadal axis by increased hypothalamic secretion of gonadotrophin-releasing hormone (GnRH) is an essential step in the process. The current hypothesis postulates that a loss of transsynaptic inhibition and a rise in excitatory inputs are responsible for the activation of GnRH release. Similarly, a shift in the balance in the expression of puberty activating and puberty inhibitory genes exists during the pubertal transition. In addition, recent evidence suggests that the epigenetic machinery controls this genetic balance, giving rise to the tantalising possibility that epigenetics serves as a relay of environmental signals known for many years to modulate pubertal development. Here, we review the contribution of epigenetics as a regulatory mechanism in the hypothalamic control of female puberty.

Disentangling puberty: novel neuroendocrine pathways and mechanisms for the control of mammalian puberty

BACKGROUND

Puberty is a complex developmental event, controlled by sophisticated regulatory networks that integrate peripheral and internal cues and impinge at the brain centers driving the reproductive axis. The tempo of puberty is genetically determined but is also sensitive to numerous modifiers, from metabolic and sex steroid signals to environmental factors. Recent epidemiological evidence suggests that the onset of puberty is advancing in humans, through as yet unknown mechanisms. In fact, while much knowledge has been gleaned recently on the mechanisms responsible for the control of mammalian puberty, fundamental questions regarding the intimate molecular and neuroendocrine pathways responsible for the precise timing of puberty and its deviations remain unsolved.

OBJECTIVE AND RATIONALE

By combining data from suitable model species and humans, we aim to provide a comprehensive summary of our current understanding of the neuroendocrine mechanisms governing puberty, with particular focus on its central regulatory pathways, underlying molecular basis and mechanisms for metabolic control.

SEARCH METHODS

A comprehensive MEDLINE search of articles published mostly from 2003 to 2017 has been carried out. Data from cellular and animal models (including our own results) as well as clinical studies focusing on the pathophysiology of puberty in mammals were considered and cross-referenced with terms related with central neuroendocrine mechanisms, metabolic control and epigenetic/miRNA regulation.

OUTCOMES

Studies conducted during the last decade have revealed the essential role of novel central neuroendocrine pathways in the control of puberty, with a prominent role of kisspeptins in the precise regulation of the pubertal activation of GnRH neurosecretory activity. In addition, different transmitters, including neurokinin-B (NKB) and, possibly, melanocortins, have been shown to interplay with kisspeptins in tuning puberty onset. Alike, recent studies have documented the role of epigenetic mechanisms, involving mainly modulation of repressors that target kisspeptins and NKB pathways, as well as microRNAs and the related binding protein, Lin28B, in the central control of puberty. These novel pathways provide the molecular and neuroendocrine basis for the modulation of puberty by different endogenous and environmental cues, including nutritional and metabolic factors, such as leptin, ghrelin and insulin, which are known to play an important role in pubertal timing.

WIDER IMPLICATIONS

Despite recent advancements, our understanding of the basis of mammalian puberty remains incomplete. Complete elucidation of the novel neuropeptidergic and molecular mechanisms summarized in this review will not only expand our knowledge of the intimate mechanisms responsible for puberty onset in humans, but might also provide new tools and targets for better prevention and management of pubertal deviations in the clinical setting.