Genetic approaches to stature, pubertal timing, and other complex traits

Early-life adversities and later-life reproductive patterns in women with fully traced reproductive history

One of the most crucial determinants of early-life development is the experience of childhood adversities. However, limited evidence is available for how these experiences shape later-life reproductive outcomes in women. Here we test the association between early-life adversities and reproductive parameters in women. Post-reproductive women (N = 105; mean age = 59.7; SD = 10.09) were recruited at the Mogielica Human Ecology Study Site in Poland within a traditional population with a low prevalence of birth control usage and fully traced reproductive histories. Reproductive parameters, as well as exposure to early-life abuse and neglect, were assessed using questionnaires. Childhood adversity was associated negatively with age at menarche (p = 0.009). Analyses on specific subtypes revealed that compared to women who did not experience any kind of early-life adversities in childhood, those who were exposed to emotional (p = 0.007) and physical (p = 0.023) neglect had an earlier age at menarche, those who experienced emotional abuse reported an earlier age at first birth (p = 0.035), and those who were exposed to physical abuse gave birth to fewer number of sons (p = 0.010). Our results suggest that women exposed to childhood adversities experience earlier physiological reproductive readiness and timing of the first birth, but their overall biological condition might be impaired as they bear fewer sons.

Efficacy and Safety of Leuprolide Acetate 6-Month Depot for the Treatment of Central Precocious Puberty: A Phase 3 Study

Context

Treatment options for central precocious puberty (CPP) are important for individualization of therapy.

Objective

We evaluated the efficacy and safety of 6-month 45-mg leuprolide acetate (LA) depot with intramuscular administration.

Methods

LA depot was administered at weeks 0 and 24 to treatment-naïve (n = 27) or previously treated (n = 18) children with CPP in a phase 3, multicenter, single-arm, open-label study (NCT03695237). Week 24 peak-stimulated luteinizing hormone (LH) suppression (<4 mIU/mL) was the primary outcome. Secondary/other outcomes included basal sex hormone suppression (girls, estradiol <20 pg/mL; boys, testosterone <30 ng/dL), suppression of physical signs, height velocity, bone age, patient/parent-reported outcomes, and adverse events.

Results

All patients (age, 7.8 ± 1.27 years) received both scheduled study doses. At 24 weeks, 39/45 patients (86.7%) had LH suppressed. Six were counted as unsuppressed; 2 because of missing data, 3 with LH of 4.35-5.30 mIU/mL and 1 with LH of 21.07 mIU/mL. Through 48 weeks, LH, estradiol, and testosterone suppression was achieved in ≥86.7%, ≥97.4%, and 100%, respectively (as early as week 4 for LH and estradiol and week 12 for testosterone). Physical signs were suppressed at week 48 (girls, 90.2%; boys, 75.0%). Mean height velocity ranged 5.0 to 5.3 cm/year post-baseline in previously treated patients and declined from 10.1 to 6.5 cm/year at week 20 in treatment-naïve patients. Mean bone age advanced slower than chronological age. Patient/parent-reported outcomes remained stable. No new safety signals were identified. No adverse event led to treatment discontinuation.

Conclusion

Six-month intramuscular LA depot demonstrated 48-week efficacy with a safety profile consistent with other GnRH agonist formulations.

Examination of pubertal timing and tempo in females and males with autism spectrum disorder compared to typically developing youth

Autism spectrum disorder (ASD) is characterized by impaired social communication and poor adaptation to change; thus, pubertal development may be precarious. Pubertal timing and tempo were measured in 244 youth (7.9% Black, 83.3% White, and 8.7% multiracial) with ASD (N = 140) and typical development (N = 104). Pubertal development was measured using Tanner staging of Genital (G, males), Breast (B, females), and pubic hair (PH) in both sexes at Year 1 (10-13 years), Year 2 (11-14 years), and Year 3 (12-15 years). Nonlinear mixed effects models analyzed interindividual differences in timing and tempo. For both sexes, ASD and higher body mass index were associated with earlier pubertal timing. Males generally exhibited faster tempo than females. Linear regression models did not show associations between pubertal timing and internalizing symptoms at time three. Findings showing advanced pubertal maturation in ASD youth suggest greater risk of psychological, social, and physiological challenges. LAY SUMMARY: Youth with ASD have difficulty in social communication and adaption to change, thus puberty may be a challenging transition. The study examined onset (timing) and progression (tempo) of puberty over three years, using physical exam, in 244 adolescents with and without ASD, enrolled at ages 10-13. ASD youth started puberty earlier, while males generally progressed at a faster pace. Further examination of puberty in ASD should identify impact on social, behavioral, and mental health outcomes.

Treatment of congenital hypogonadotropic hypogonadism in male patients

Congenital hypogonadotropic hypogonadism (CHH) is characterized by complete or partial failure of pubertal development because of inadequate secretion of gonadotropic hormones. CHH consists of hypogonadotropic hypogonadism with anosmia or hyposmia, Kallmann syndrome, and the normosmic variation normosmic idiopathic hypogonadotropic hypogonadism. CHH is one of the few treatable diseases of male infertility, although men with primary testicular dysfunction have irreversibly diminished spermatogenic capacity. The approach to CHH treatment is determined by goals such as developing virilization or inducing fertility. This review focuses on the current knowledge of therapeutic modalities for inducing puberty and fertility in men with CHH.

Puberty and growth in patients with pediatric intestinal failure

BACKGROUND

Pediatric intestinal failure (PIF) affects nutrition, metabolism, and endocrine development, but its downstream impact on puberty is unknown.

METHODS

A retrospective review was performed of patients age >8 years with PIF managed at an intestinal rehabilitation program. Outcomes of interest were peak height velocity (PHV), age at PHV, and age at pubertal onset (Tanner stage 2). Outcomes were stratified by sex and compared to established norms.

RESULTS

Of 110 patients with PIF, 54.5% were male. Compared to the CDC 50th percentile, PHV in PIF patients was similar for females (8.09±2.36 vs. 7.37 cm/yr;p = 0.23) but significantly higher for males (9.27±2.56 vs. 7.91 cm/yr;p = 0.038). Age at PHV in PIF patients was significantly younger for both males (12.31±2.14 vs. 13.38 years;p = 0.049) and females (10.70±1.06 vs. 11.71 years;p = 0.001). PIF patients reached pubertal onset earlier than published norms; this was significant for males (12.41±1.80 vs. 13.44 years;p = 0.014), but not for females (10.45±1.81 vs. -11.15 years;p = 0.13). The mean height-for-age Z-score was -1.2, with 20% of patients having a Z-score less than -2.

CONCLUSIONS

Pubertal onset and growth are neither delayed nor diminished in patients with PIF. The high incidence of short stature, however, highlights the importance of optimizing prepubertal linear growth to attain full height potential.

TYPE OF STUDY

Prognosis study (Retrospective cohort study).

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.

Genetics of pubertal timing

Puberty marks the end of childhood and is a period when individuals undergo physiological and psychological changes to achieve sexual maturation and fertility. The onset of puberty is first detected as an increase in pulsatile secretion of gonadotropin-releasing hormone (GnRH). Pubertal onset is regulated by genetic, nutritional, environmental, and socio-economic factors. Disturbances affecting pubertal timing result in adverse health conditions later in life. Human genetic studies show that around 50-80% of the variation in pubertal onset is genetically determined. The genetic control of pubertal timing has been a field of active investigation in attempt to better understand the neuroendocrine control of this relevant period of life. Large populational studies and patient cohort-based studies have provided insights into the genetic regulation of pubertal onset. In this review, we discuss these discoveries and discuss potential mechanisms for how implicated genes may affect pubertal timing.

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.

[Clinical and molecular genetic features of 3 family cases of the central precocious puberty, due to MKRN3 gene defects]

Gonadotropin-dependent precocious puberty (central) is a condition resulting from the early (up to 8 years in girls and 9 years in boys) reactivation of the hypothalamic-pituitary-gonadal axis. An increase in the secretion of sex steroids by the gonads in this form is a consequence of the stimulation of the sex glands by gonadotropic hormones of the pituitary gland. In the absence of central nervous system abnormalities, CPP is classified as idiopathic and as familial in some cases, emphasizing the genetic origin of this disorder. Loss-of-function mutations in Makorin Ring Finger Protein 3 (MKRN3) are the most common identified genetic cause of central precocious puberty compared to sporadic cases. In the present study we performed the first descrition of 3 family cases of central precocious puberty duo to novel MKRN3 gene mutation detected by NGS in the Russian Federation.

Delayed and Precocious Puberty: Genetic Underpinnings and Treatments

Delayed puberty may signify a common variation of normal development, or indicate the presence of a pathologic process. Constitutional delay of growth and puberty is a strongly familial type of developmental pattern and accounts for the vast majority of children who are "late bloomers." Individuals with sex chromosomal abnormalities frequently have hypergonadotropic hypogonadism. There are currently 4 known monogenic causes of central precocious puberty. The primary treatment goal in children with hypogonadism is to mimic normal pubertal progression, while the primary aims for the management of precocious puberty are preservation of height potential and prevention of further pubertal development.

Novel Mutations and Genes That Impact on Growth in Short Stature of Undefined Aetiology: The EPIGROW Study

BACKGROUND

Children with short stature of undefined aetiology (SS-UA) may have undiagnosed genetic conditions.

PURPOSE

To identify mutations causing short stature (SS) and genes related to SS, using candidate gene sequence data from the European EPIGROW study.

METHODS

First, we selected exonic single nucleotide polymorphisms (SNPs), in cases and not controls, with minor allele frequency (MAF) < 2%, whose carriage fitted the mode of inheritance. Known mutations were identified using Ensembl and gene-specific databases. Variants were classified as pathogenic, likely pathogenic, or variant of uncertain significance using criteria from the American College of Medical Genetics and Genomics and the Association for Molecular Pathology. If predicted by ≥ 5/10 algorithms (eg, Polyphen2) to be deleterious, this was considered supporting evidence of pathogenicity. Second, gene-based burden testing determined the difference in SNP frequencies between cases and controls across all and then rare SNPs. For genotype/phenotype relationships, we used PLINK, based on haplotype, MAF > 2%, genotype present in > 75%, and Hardy Weinberg equilibrium P > 10-4.

RESULTS

First, a diagnostic yield of 10% (27/263) was generated by 2 pathogenic (nonsense in ACAN) and a further 25 likely pathogenic mutations, including previously known missense mutations in FANCB, IGFIR, MMP13, NPR2, OBSL1, and PTPN11. Second, genes related to SS: all methods identified PEX2. Another 7 genes (BUB1B, FANCM, CUL7, FANCA, PTCH1, TEAD3, BCAS3) were identified by both gene-based approaches and 6 (A2M, EFEMP1, PRKCH, SOS2, RNF135, ZBTB38) were identified by gene-based testing for all SNPs and PLINK.

CONCLUSIONS

Such panels improve diagnosis in SS-UA, extending known disease phenotypes. Fourteen genes related to SS included some known to cause growth disorders as well as novel targets.

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.

Association study of DLK1 in girls with idiopathic central precocious puberty

Objective Mutations in the delta-like 1 homolog (DLK1) gene have recently been reported in patients with idiopathic central precocious puberty (CPP). We aimed to investigate DLK1 mutations or polymorphisms in girls with CPP. Methods A total of 100 girls diagnosed with idiopathic CPP were enrolled. DLK1 coding regions were sequenced in girls with idiopathic CPP and healthy girls (controls). The relationship between identified sequence variations and CPP was evaluated via comparison of allele frequencies between patients with CPP and normal healthy controls. Results We identified five polymorphisms in DLK1. There was no significant difference with regard to allele frequency between patients with CPP and controls. Polymorphism c.549C>T (p.G183G) in DLK1 gene was identified in only one patient with CPP. In silico analysis with human splicing finder suggested that the variant (c.549C>T) leads to splicing defect. Conclusions The sequencing of DLK1 gene has uncovered only one potentially meaningful variant. However, our results demonstrate that DLK1 mutations are a relatively rare cause of idiopathic CPP.

Central Precocious Puberty Caused by Novel Mutations in the Promoter and 5'-UTR Region of the Imprinted MKRN3 Gene

Background: Central Precocious Puberty (CPP) is clinically defined by the development of secondary sexual characteristics before the age of 8 years in girls and 9 years in boys. To date, mutations in the coding region of KISS1, KISS1R, PROKR2, DLK1, and MKRN3 genes have been reported as causative for CPP. This study investigated the presence of causative mutations in both the promoter and the 5'-UTR regions of the MKRN3 gene. Methods: Sanger DNA sequencing was used for screening the proximal promoter and 5'-UTR region of the MKRN3 gene in a group of 73 index girls with CPP. Mutations identified were cloned in luciferase reporter gene vectors and transiently transfected in GN11 cells in order to check for changes in the activity of the MKRN3 promoter. GN11 cells were previously checked for Mkrn3 expression using lentivirus mediated knock-down. In silico analysis was implemented for the detection of changes in the mRNA secondary structure of the mutated MKRN3 5'-UTR. Results: Three novel heterozygous mutations (-166, -865, -886 nt upstream to the transcription start site) located in the proximal promoter region of the MKRN3 gene were identified in six non-related girls with CPP. Four of these girls shared the -865 mutation, one the -166, and another one the -886. A 5'-UTR (+13 nt downstream to the transcription start site) novel mutation was also identified in a girl with similar clinical phenotype. Gene reporter assay evaluated the identified promoter mutations and demonstrated a significant reduction of MKRN3 promoter activity in transfected GN11 cells. In silico analysis for the mutated 5'-UTR predicted a significant change of the mRNA secondary structure. The minimum free energy (MFE) of the mutated 5'-UTR was higher when compared to the corresponding wild-type indicating less stable RNA secondary structure. Conclusion: Our findings demonstrated novel genetic alterations in the promoter and 5'-UTR regulatory regions of the MKRN3 gene. These changes add to another region to check for the etiology of CPP.

Precocious and Early Central Puberty in Children With Pre-existing Medical Conditions: A Single Center Study

Background: Precocious and early puberty are reported findings in children with pre-existing medical conditions including certain syndromes. Series pertaining to such situations are limited. Methods: A retrospective, single-center study was conducted on children with central precocious puberty (onset before the age of 8 years in girls and 9 years in boys) or early puberty (onset between 8 and 9 years in girls and between 9 and 10.5 years in boys) diagnosed on the background of a known pre-existing chronic significant medical condition. Patients with a CNS tumor and those exposed to cranial irradiation were excluded. Results: Precocious puberty was diagnosed in 13 patients and early puberty in 12. Mean age at onset of puberty was 6.65 ± 2.3 years in girls (n = 15) and 9.4 ± 0.84 years in boys (n = 10). The most common disorders were psychomotor delay (n = 12), psychiatric disorders (n = 7) and/or epilepsy (n = 5). Precocious or early puberty was among the symptoms experienced by patients with a variety of syndromes including lipofuscinosis (2 siblings), Dravet syndrome and Silver-Russel syndrome. Pituitary stalk interruption with agenesis of olfactory bulbs and optic nerve atrophy was found on imaging in one patient who presented with blindness, epilepsy, and autism spectrum disorder. The other diseases associated with precocious or early puberty are adrenocorticotropic deficiency, dyspraxia and bone abnormalities, glomerulopathy with complete renal failure, and repeated intra-fetal deaths in the mother. Karyotype analysis revealed chromosomal duplication (chromosome 15 in 2 cases; chromosomes 17 and 11 in one case each) in 4 of 8 patients evaluated. Conclusions: Data from patients with complex disease who experience precocious or early puberty may provide clues regarding the genetic determinants of pubertal development.

Makorin 1 Regulates Developmental Timing in Drosophila

The central mechanisms coordinating growth and sexual maturation are well conserved across invertebrates and vertebrates. Although mutations in the gene encoding makorin RING finger protein 3 (mkrn3 ) are associated with central precocious puberty in humans, a causal relationship has not been elucidated. Here, we examined the role of mkrn1, a Drosophila ortholog of mammalian makorin genes, in the regulation of developmental timing. Loss of MKRN1 in mkrn1 exS prolonged the 3rd instar stage and delayed the onset of pupariation, resulting in bigger size pupae. MKRN1 was expressed in the prothoracic gland, where the steroid hormone ecdysone is produced. Furthermore, mkrn1 exS larvae exhibited reduced mRNA levels of phantom, which encodes ecdysone-synthesizing enzyme and E74, which is a downstream target of ecdysone. Collectively, these results indicate that MKRN1 fine-tunes developmental timing and sexual maturation by affecting ecdysone synthesis in Drosophila. Moreover, our study supports the notion that malfunction of makorin gene family member, mkrn3 dysregulates the timing of puberty in mammals.

Methylome profiling of healthy and central precocious puberty girls

Background

Recent studies demonstrated that changes in DNA methylation (DNAm) and inactivation of two imprinted genes (MKRN3 and DLK1) alter the onset of female puberty. We aimed to investigate the association of DNAm profiling with the timing of human puberty analyzing the genome-wide DNAm patterns of peripheral blood leukocytes from ten female patients with central precocious puberty (CPP) and 33 healthy girls (15 pre- and 18 post-pubertal). For this purpose, we performed comparisons between the groups: pre- versus post-pubertal, CPP versus pre-pubertal, and CPP versus post-pubertal.

Results

Analyzing the methylome changes associated with normal puberty, we identified 120 differentially methylated regions (DMRs) when comparing pre- and post-pubertal healthy girls. Most of these DMRs were hypermethylated in the pubertal group (99%) and located on the X chromosome (74%). Only one genomic region, containing the promoter of ZFP57, was hypomethylated in the pubertal group. ZFP57 is a transcriptional repressor required for both methylation and imprinting of multiple genomic loci. ZFP57 expression in the hypothalamus of female rhesus monkeys increased during peripubertal development, suggesting enhanced repression of downstream ZFP57 target genes. Fourteen other zinc finger (ZNF) genes were related to the hypermethylated DMRs at normal puberty. Analyzing the methylome changes associated with CPP, we demonstrated that the patients with CPP exhibited more hypermethylated CpG sites compared to both pre-pubertal (81%) and pubertal (89%) controls. Forty-eight ZNF genes were identified as having hypermethylated CpG sites in CPP.

Conclusion

Methylome profiling of girls at normal and precocious puberty revealed a widespread pattern of DNA hypermethylation, indicating that the pubertal process in humans is associated with specific changes in epigenetically driven regulatory control. Moreover, changes in methylation of several ZNF genes appear to be a distinct epigenetic modification underlying the initiation of human puberty.

Electronic supplementary material

The online version of this article (10.1186/s13148-018-0581-1) contains supplementary material, which is available to authorized users.

Detecting genetic regions associated with height in the native ponies of the British Isles by using high density SNP genotyping

Height is an important characteristic in the equine industry although little is known about its genetic control in native British breeds of ponies. This study aimed to map QTL data with the withers height in four pony breeds native to the British Isles, including two different sections within Welsh Cobs. In this study, a genome-wide analysis approach using the Illumina EquineSNP50 Infinium BeadChip was applied to 105 ponies and cobs. Analysis identified 222 highly significant height-associated SNPs (P ≤ 10^-5), among which three SNPs on ECA9 have also been previously reported elsewhere. The highest number of significant SNPs associated to height in the native British horses were located on ECA1, ECA8, and ECA16.

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.

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.

Gene expression profiling of puberty-associated genes reveals abundant tissue and sex-specific changes across postnatal development

The timing of human puberty is highly variable, sexually dimorphic, and associated with adverse health outcomes. Over 20 genes carrying rare mutations have been identified in known pubertal disorders, many of which encode critical components of the hypothalamic-pituitary-gonadal (HPG) axis. Recent genome-wide association studies (GWAS) have identified more than 100 candidate genes at loci associated with age at menarche or voice breaking in males. We know little about the spatial, temporal or postnatal expression patterns of the majority of these puberty-associated genes. Using a high-throughput and sensitive microfluidic quantitative PCR strategy, we profiled the gene expression patterns of the mouse orthologs of 178 puberty-associated genes in male and female mouse HPG axis tissues, the pineal gland, and the liver at five postnatal ages spanning the pubertal transition. The most dynamic gene expression changes were observed prior to puberty in all tissues. We detected known and novel tissue-enhanced gene expression patterns, with the hypothalamus expressing the largest number of the puberty-associated genes. Notably, over 40 puberty-associated genes in the pituitary gland showed sex-biased gene expression, most of which occurred peri-puberty. These sex-biased genes included the orthologs of candidate genes at GWAS loci that show sex-discordant effects on pubertal timing. Our findings provide new insight into the expression of puberty-associated genes and support the possibility that the pituitary plays a role in determining sex differences in the timing of puberty.

The mystery of puberty initiation: genetics and epigenetics of idiopathic central precocious puberty (ICPP)

Puberty is a major developmental stage. Damaging mutations, considered as "mistakes of nature", have contributed to the unraveling of the networks implicated in the normal initiation of puberty. Genes involved in the abnormal hypothalamic-pituitary-gonadal (HPG) axis development, in the normosmic idiopathic hypogonadotropic hypogonadism (nIHH), in the X-linked or autosomal forms of Kallmann syndrome and in precocious puberty have been identified (GNRH1, GNRHR, KISS1, GPR54, FGFR1, FGF8, PROK2, PROKR2, TAC3, TACR3, KAL1, PROK2, PROKR2, CHD7, LEP, LEPR, PC1, DAX1, SF-1, HESX-1, LHX3, PROP-1). Most of them were found to play critical roles in HPG axis development and regulation, the embryonic GnRH neuronal migration and secretion, the regulation and action of the hypothalamic GnRH. However, the specific neural and molecular mechanisms triggering GnRH secretion remain one of the scientific enigmas. Although GnRH neurons are probably capable of autonomously generating oscillations, many gonadal steroid-dependent and -independent mechanisms have also been proposed. It is now well proven that the secretion of GnRH is regulated by kisspeptin as well as by permissive or opposing signals mediated by neurokinin B and dynorphin. These three supra-GnRH regulators compose the kisspeptin-neurokinin B-dynorphin neuronal (KNDy) system, a key player in pubertal onset and progression. Moreover, an ongoing increasing number of inhibitory, stimulatory and permissive networks acting upstream on GnRH neurons, such as GABA, NPY, LIN28B, MKRN3 and others integrate diverse hormonal and peripheral signals and have been proposed as the "gate-keepers" of puberty, while epigenetic modifications play also an important role in puberty initiation.

Clinical Exome Sequencing Reveals MKRN3 Pathogenic Variants in Familial and Nonfamilial Idiopathic Central Precocious Puberty

BACKGROUND/AIMS

Idiopathic central precocious puberty (ICPP) is the premature activation of the hypothalamic-pituitary-gonadal axis in the absence of organic disease. Up to now, just gain-of-function mutations of KISS1/KISS1R and loss-of-function mutations of the maternally imprinted gene MKRN3 are the known genetic causes of ICPP. Our intention is to evaluate variants present in genes related to the pubertal onset pathway that could act as disease-causing or predisposing variants.

METHODS

We studied the clinical exome of 20 patients diagnosed with ICPP using the Illumina platform. The bioinformatics analysis was performed using 2 different programs, and the variants were filtered according to a list of genes related to the gonadotropin-releasing hormone pathway.

RESULTS

In a "sporadic case," we found a missense variant in MKRN3 NM_005664.3: c.203G>A, causing the protein change NP_005655.1:p.Arg68His, predicted as pathogenic by 2 informatics tools. The proband carrying this variant was diagnosed with ICPP at 7.75 years of age. We did not find any pathogenic variants in KISS1, KISS1R, LIN28, GNRH, GNRHR, TACR3, and TAC3.

CONCLUSION

MKRN3 is the most frequent genetic cause of familial ICPP, so it is wise to screen for MKRN3 mutations in all patients with familial ICPP and in patients with an unclear paternal pubertal history.

Genetic Determinants of Prepubertal and Pubertal Growth and Development

This article surveys the current general understanding of genetic influences on within- and between-population variation in growth and development in the context of establishing an International Growth Standard for Preadolescent and Adolescent Children. Traditional genetic epidemiologic analysis methods are reviewed, and evidence from family studies for genetic effects on different measures of growth and development is then presented. Findings from linkage and association studies seeking to identify specific genomic locations and allelic variants of genes influencing variation in growth and maturation are then summarized. Special mention is made of the need to study the interactions between genes and environments. At present, specific genes and polymorphisms contributing to variation in growth and maturation are only beginning to be identified. Larger genetic epidemiologic studies are needed in different parts of the world to better explore population differences in gene frequencies and gene—environment interactions. As advances continue to be made in molecular and statistical genetic methods, the genetic architecture of complex processes, including those of growth and development, will become better elucidated. For now, it can only be concluded that although the fundamental genetic underpinnings of the growth and development of children worldwide are likely to be essentially the same, there are also likely to be differences between populations in the frequencies of allelic gene variants that influence growth and maturation and in the nature of gene–environment interactions. This does not necessarily preclude an international growth reference, but it does have important implications for the form that such a reference might ultimately take.

Treatment of growth hormone deficiency in children, adolescents and at the transitional age

Recombinant human growth hormone (rhGH) has been available since 1985. Before 1985 growth hormone (GH) was extracted from cadaveric pituitary glands, but this was stopped in most countries that year, following the recognition that it could transmit Creutzfeldt-Jacob disease. The primary goal of rhGH treatment in GHD patients is to normalize height during childhood and adolescence and attain an adult height within the normal range and within the target height range (genetic potential). Genome-wide association studies have been used increasingly to study the genetic influence on height. There is a wide response to rhGH therapy, likely due to compliance issues, severity of GH deficiency and patient's sensitivity to rhGH. While some pediatric endocrinologists will use a fixed dose of rhGH, most will use an auxology-based dosing approach. This will involve starting at the lower end of the dose range and then titrating upwards based on the patient's response to therapy with measurement of IGF-1 concentrations to ensure that the patient is not over treated or undertreated. Although treatment of children with GHD with rhGH has generally been safe, careful follow-up by a pediatric endocrinologist in partnership with the pediatrician or primary care physician is recommended. The aim of this paper is to review the strategies and recommendations for treatment of GHD in children and patients in the transition to adult care.

Relationship between menarche and psychosis onset in women with first episode of psychosis

AIM

The aim of this study was to explore the relationship between age at menarche and age at first episode of psychosis, as well as clinical severity and outcome, in a population of women with first-episode psychosis.

METHODS

Clinical and socio-demographical data, age at menarche and at first-episode psychosis, parental history of psychosis and cannabis-use habits were obtained from 42 subjects with a first episode of psychosis. Positive and Negative Syndrome Scale, Clinical Global Impression, Global Assessment Function, Disability Assessment Schedule, Wechsler Adult Intelligence Scale and Wechsler Intelligence Scale for Children, European Quality of Life, and Lewis and Murray Obstetric Complication Scales were administered. Statistical analysis was performed by means of zero-order correlations and Mann-Whitney U and Kruskal-Wallis tests using SPSS version 17.0.

RESULTS

We found no significant correlation between age at menarche and age at first-episode psychosis, or with the clinical scores performed. We observed that subjects with earlier age at menarche had more parental history of psychosis.

CONCLUSIONS

Our negative results do not support the theory of a possible protective role of oestrogen, which seems to be more complex than previously thought. We would suggest that further research is needed to investigate developmental influences of sex steroids on the onset of psychosis and potentially therapeutic benefits based upon oestrogen.

Pubertal development and regulation

Puberty marks the end of childhood and is a period when individuals undergo physiological and psychological changes to achieve sexual maturation and fertility. The hypothalamic-pituitary-gonadal axis controls puberty and reproduction and is tightly regulated by a complex network of excitatory and inhibitory factors. This axis is active in the embryonic and early postnatal stages of life and is subsequently restrained during childhood, and its reactivation culminates in puberty initiation. The mechanisms underlying this reactivation are not completely known. The age of puberty onset varies between individuals and the timing of puberty initiation is associated with several health outcomes in adult life. In this Series paper, we discuss pubertal markers, epidemiological trends of puberty initiation over time, and the mechanisms whereby genetic, metabolic, and other factors control secretion of gonadotropin-releasing hormone to determine initiation of puberty.

In silico analysis of a novel MKRN3 missense mutation in familial central precocious puberty

BACKGROUND

The onset of puberty is influenced by the interplay of stimulating and restraining factors, many of which have a genetic origin. Premature activation of the GnRH secretion in central precocious puberty (CPP) may arise either from gain-of-function mutations of the KISS1 and KISS1R genes or from loss-of-function manner mutations of the MKRN3 gene leading to MKRN3 deficiency.

OBJECTIVE

To explore the genetic causes responsible for CPP and the potential role of the RING finger protein 3 (MKRN3) gene.

DESIGN AND PATIENTS

We investigated potential sequence variations in the intronless MKRN3 gene by Sanger sequencing of the entire 507 amino acid coding region of exon 1 in a family with two affected girls presented with CPP at the age of 6 and 5·7 years, respectively.

RESULTS

A novel heterozygous g.Gly312Asp missense mutation in the MKRN3 gene was identified in these siblings. The imprinted MKRN3 missense mutation was also identified as expected in the unaffected father and followed as expected an imprinted mode of inheritance. In silico analysis of the altered missense variant using the computational algorithms Polyphen2, SIFT and Mutation Taster predicted a damage and pathogenic alteration causing CPP. The pathogenicity of the alteration at the protein level via an in silico structural model is also explored.

CONCLUSION

A novel mutation in the MKRN3 gene in two sisters with CPP was identified, supporting the fundamental role of this gene in the suppression of the hypothalamic GnRH neurons.

A case of familial central precocious puberty caused by a novel mutation in the makorin RING finger protein 3 gene

BACKGROUND

Central precocious puberty (CPP) is often familial but its genetic cause is largely unknown. Very recently, the makorin RING finger protein 3 (MKRN3) gene, located on chromosome 15 in the Prader-Willi syndrome (PWS)-associated region (15q11-q13), has been found mutated in 5 families with familial precocious puberty. The MKRN3 is a maternal imprinted gene and the phenotype is expressed only when the MKRN3 mutations are localized on the allele inherited from the father. The function of this gene is not completely known and the phenotype caused by its defect is not yet fully elucidated. We report a new MKRN3 mutation (Pro160Cysfs*14) causing familial CPP.

CASE PRESENTATION

The index case is a 7 years old girl showing Tanner stage 3 and pubic hair stage 1. Her bone age evaluated by TW2 method was 10.3 years. Her hormonal data confirmed the diagnosis of central precocious puberty. Familial medical history revealed precocious puberty in a cousin on paternal side. Paternal grandmother had menarche at the age of 9 years and 6 months and premature menopause when she was 36 years old. Genetic analysis revealed a new mutation (c477_485del; Pro160Cysfs*14) in the maternally imprinted MKRN3. Puberty onset was at 5 years in the other affected female family member. Precocious puberty was well controlled by pharmacological therapy.

CONCLUSION

We expand the number of the MKRN3 mutations associated with CPP and highlight the importance of an accurate family medical history to disclose the peculiar pattern of inheritance of this gene.

Hormone replacement therapy in children: The use of growth hormone and IGF-I

Recombinant human GH (rhGH) has been available since 1985. This article gives an overview, what has been achieved over the past 30 years in respect to optimization of rhGH treatment for the individual child with GH deficiency and what are the safety issues concerned with this treatment. In the last twenty years significant scientific progress has been made in the diagnosis of GH deficiency, the genetic disorders that are associated with pituitary GH deficiency and the genetics that influence growth in general. On the other hand rhGH is not only used in states of GH deficiency but also various conditions without a proven GH deficiency by classical standards. Clinical studies that investigated both the genetics of growth and the individual responses to rhGH therapy in these patient populations were able to refine our concept about the physiology of normal growth. In most patients under rhGH treatment there is a considerable short-term effect, however the overall gain in growth obtained by a long-term treatment until final height still remains a matter of debate in some of the conditions treated. Also first studies on the long-term safety risks of rhGH treatment have raised the question whether this treatment is similarly safe for all the patient groups eligible for such a treatment. Therefore even in the face of a longstanding safety record of this drug replacement therapy the discussion about the right cost and risk to benefit ratio is continuing. Consequently there is still a need for carefully conducted long-term studies that use modern anthropometric, genetic, and laboratory techniques in order to provide the necessary information for clinicians to select the patients that will benefit best from this valuable treatment without any long term risk.

Subtraction suppressive hybridisation analysis of differentially expressed genes associated with puberty in the goat hypothalamus

The cost of developing replacement nanny goats could be reduced by decreasing the age at puberty because this way nanny goats could be brought into production at an earlier age. The aim of the present study was to screen genes related to puberty to investigate the molecular mechanisms of puberty. Subtracted cDNA libraries were constructed for hypothalami from juvenile (Group A), pubertal (Group B) and age-matched control pubertal (Group E) Jining grey (JG) and Liaoning cashmere (LC) goats using suppression subtractive hybridisation (SSH). Differentially expressed genes were analysed by bioinformatics methods. There were 203 expressed sequence tags (ESTs) in the subtracted cDNA libraries that were differentially expressed between JG and LC goats at the juvenile stage, 226 that were differentially expressed at puberty and 183 that were differentially expressed in the age-matched control group. The differentially expressed ESTs in each subtracted cDNA library were classified as known gene, known EST and unknown EST according to sequence homology in the GenBank non-redundant (NR) and EST database. According to gene function analysis in the COG (Cluster of Orthologous Groups) database, the known genes were grouped into 10 subdivisions in Group A, into seven subdivisions in Group E and into nine subdivisions in Group B under three categories: cellular processes and signalling, information storage and processing, and metabolism. Pathway analysis in the KEGG (Kyoto Encyclopedia of Genes and Genomes) pathway database of known genes revealed that the three pathways that most differentially expressed genes were involved in were metabolic pathways, Parkinson's disease and oxidative phosphorylation. Protein interaction analysis of the high homology genes revealed the most dominant network to be structure of ribosome/protein translation, oxidative phosphorylation and carbohydrate metabolism. The results reveal that the onset of puberty is a complex event involving multiple genes in multiple biological processes. The differentially expressed genes include genes related to both neuroendocrine and energy metabolism.

Genome-scan analysis for genetic mapping of quantitative trait loci underlying birth weight and onset of puberty in doe kids (Capra hircus)

The objective of this study was to locate quantitative trait loci (QTL) causing variation in birth weight and age of puberty of doe kids in a population of Rayini cashmere goats. Four hundred and thirty kids from five half-sib families were genotyped for 116 microsatellite markers located on the caprine autosomes. The traits recorded were birth weight of the male and female kids, body weight at puberty, average daily gain from birth to age of puberty and age at puberty of the doe kids. QTL analysis was conducted using the least squares interval mapping approach. Linkage analysis indicated significant QTL for birth weight on Capra hircus chromosomes (CHI) 4, 5, 6, 18 and 21. Five QTL located on CHI 5, 14 and 29 were associated with age at puberty. Across-family analysis revealed evidence for overlapping QTL affecting birth weight (78 cM), body weight at puberty (72 cM), average daily gain from birth to age of puberty (72 cM) and age at puberty (76 cM) on CHI 5 and overlapping QTL controlling body weight at puberty and age at puberty on CHI 14 at 18-19 cM. The proportion of the phenotypic variance explained by the detected QTL ranged between 7.9% and 14.4%. Confirming some of the previously reported results for birth weight and growth QTL in goats, this study identified more QTL for these traits and is the first report of QTL for onset of puberty in doe kids.

Attenuated hypothalamic-pituitary-adrenal axis functioning predicts accelerated pubertal development in girls 1 year later

Accelerated pubertal development has been linked to adverse early environments and may heighten subsequent mental and physical health risks. Hypothalamic-pituitary-adrenal axis functioning has been posited as a mechanism whereby stress may affect pubertal development, but the literature lacks prospective tests of this mechanism. The current study assessed 277 youth (M = 10.84 years, SD = 1.14), 138 boys and 139 girls, who reported on their pubertal development and underwent the Trier Social Stress Test for Children at baseline and returned to the laboratory approximately 1 year later (M = 1.12 years, range = 0.59-1.98 years). For girls, lower cortisol area under the curve (with respect to ground) at Time 1 predicted more advanced pubertal development at Time 2, controlling for Time 1 pubertal development. This association persisted after additional covariates including age, body mass index, race, and maltreatment history were introduced, and was driven by adrenal rather than gonadal development. Cortisol was not linked to boys' subsequent pubertal development, and no interaction by gender or by maltreatment appeared. These results suggest that attenuated cortisol, reported in other studies of children exposed to early adversity, may contribute to accelerated pubertal tempo in girls.

New causes of central precocious puberty: the role of genetic factors

A pivotal event in the onset of puberty in humans is the reemergence of the pulsatile release of the gonadotropin-releasing hormone (GnRH) from hypothalamic neurons. Pathways governing GnRH ontogeny and physiology have been discovered by studying animal models and humans with reproductive disorders. Recent human studies implicated the activation of kisspeptin and its cognate receptor (KISS1/KISS1R) and the inactivation of MKRN3 in the premature reactivation of GnRH secretion, causing central precocious puberty (CPP). MKRN3, an imprinted gene located on the long arm of chromosome 15, encodes makorin ring finger protein 3, which is involved in ubiquitination and cell signaling. The MKRN3 protein is derived only from RNA transcribed from the paternally inherited copy of the gene due to maternal imprinting. Currently, MKRN3 defects represent the most frequent known genetic cause of familial CPP. In this review, we explored the clinical, hormonal and genetic aspects of children with sporadic or familial CPP caused by mutations in the kisspeptin and MKRN3 systems, essential genetic factors for pubertal timing.

Genetic and environmental effects on age at menarche, and its relationship with reproductive health in twins

INTRODUCTION:

Menarche or first menstrual period is a landmark in reproductive life span and it is the most prominent change of puberty. The timing of menarche can be under the influence of genes as well as individual environmental factors interacting with genetic factors.

OBJECTIVE:

Our study objectives were (a) to investigate the heritability of age of menarche in twins, (b) to obtain the association between age of menarche and childhood factors, and reproductive events/behavior, (c) to examine whether or not having a male co-twin affects early/late menarche.

METHODOLOGY:

A group of female-female identical (n = 108, 54 pairs), non-identical twins (n = 68, 34 pairs) and 17 females from opposite-sex twin sets were identified from twin registries of Malaysia and Iran. Genetic analysis was performed via two methods of Falconers’ formula and maximum likelihood.

RESULTS:

Heritability was found to be 66% using Falconers’ formula and 15% using univariate twin analysis. Model analysis revealed that shared environmental factors have a major contribution in determining the age of menarche (82%) followed by non-shared environment (18%).

DISCUSSION:

Result of this study is consistent with that of the literature. Timing of menarche could be under the influence of shared and non-shared environmental effects. Hirsutism was found to have a higher frequency among subjects with late menarche. There was no significant difference in age of menarche between females of opposite-sex twins and females of same-sex twins.

CONCLUSION:

It is concluded that twin models provide a powerful means of examining the total genetic contribution to age of menarche. Longitudinal studies of twins may clarify the type of environmental effects that determine the age of menarche.

Central precocious puberty caused by mutations in the imprinted gene MKRN3

BACKGROUND

The onset of puberty is first detected as an increase in pulsatile secretion of gonadotropin-releasing hormone (GnRH). Early activation of the hypothalamic-pituitary-gonadal axis results in central precocious puberty. The timing of pubertal development is driven in part by genetic factors, but only a few, rare molecular defects associated with central precocious puberty have been identified.

METHODS

We performed whole-exome sequencing in 40 members of 15 families with central precocious puberty. Candidate variants were confirmed with Sanger sequencing. We also performed quantitative real-time polymerase-chain-reaction assays to determine levels of messenger RNA (mRNA) in the hypothalami of mice at different ages.

RESULTS

We identified four novel heterozygous mutations in MKRN3, the gene encoding makorin RING-finger protein 3, in 5 of the 15 families; both sexes were affected. The mutations included three frameshift mutations, predicted to encode truncated proteins, and one missense mutation, predicted to disrupt protein function. MKRN3 is a paternally expressed, imprinted gene located in the Prader-Willi syndrome critical region (chromosome 15q11-q13). All affected persons inherited the mutations from their fathers, a finding that indicates perfect segregation with the mode of inheritance expected for an imprinted gene. Levels of Mkrn3 mRNA were high in the arcuate nucleus of prepubertal mice, decreased immediately before puberty, and remained low after puberty.

CONCLUSIONS

Deficiency of MKRN3 causes central precocious puberty in humans. (Funded by the National Institutes of Health and others.).

Estrogen receptor α polymorphism in boys with constitutional delay of growth and puberty

PURPOSE

There were a lot of reports regarding associations of polymorphisms in the estrogen receptor α (ESR1). with many disorders. But, those with constitutional delay of growth and puberty (CDGP) are not known. Our aim is to find out any association between CDGP and ESR1.

METHODS

In a total of 27 subjects, we compared 7 CDGP patients with 20 healthy controls with their heights and sexual maturity rates were within normal range. We selected three single nucleotide polymorphisms from intron 1 of ESR1 (rs3778609, rs12665044, and rs827421) as candidates, respectively.

RESULTS

In genotype analyses, the frequency of G/G genotype at rs827421 in intron 1 of ESR1 was increased in CDGP boys (P=0.03).

CONCLUSION

The genetic variation of ESR1 can be a contributing factor of tempo of growth and puberty.

Control of puberty: genetics, endocrinology, and environment

PURPOSE OF REVIEW

The aim of this review is to summarize recent advances regarding the genetic components of the complex and coordinated process of puberty, an update of the genes implicated in disorders of puberty, the endocrinologic changes of puberty, and influences of environment in the light of our current understanding of the mechanism of the onset of puberty.

RECENT FINDINGS

The timing of puberty varies greatly in the general population among ethnic groups throughout the world, suggesting the genetic control of puberty. Several studies on the pathological conditions of pubertal onset provide unique information about the interactions of either the genetic susceptibility of or environmental influences on hypothalamic control of pubertal onset. However, these findings suggested that no isolated pathway or external factor is solely responsible for the neuroendocrine control of puberty.

SUMMARY

Puberty is initiated by gonadotropin-releasing hormone from the hypothalamus followed by a complex sequence of endocrine changes and is regulated by both genetic and environmental factors. New attempts to use genetics and genomics might enhance our understanding of the spectrum of pubertal development.

Molecular biology of the kisspeptin receptor: signaling, function, and mutations

Kisspeptin receptor (KISS1R) signaling is essential for the hallmark increase in pulsatile GnRH secretion characteristic of the onset of puberty in humans and experimental animals. Loss-of-function mutations in KISS1R are associated with idiopathic hypogonadotropic hypogonadism in humans. Also, mutations with confirmed association with idiopathic central precocious puberty were identified in kisspeptin and KISS1R. These observations underscore the role of KISS1R signaling for normal pubertal development. Moreover, investigation of the mechanisms underlying the gain-of-function mutation in KISS1R indicates that the duration of KISS1R signaling is critical for the role of this receptor in timing the onset of puberty in humans. These findings further endorse the need to uncover the mechanisms, as well as yet-unknown proteins, involved in each step of KISS1R signaling. This knowledge is expected to advance our understanding of normal and abnormal pubertal development, as well as to help uncover the role of KISS1R signaling in non-hypothalamic tissues such as the placenta. This chapter discusses recent advances in the investigation of KISS1R signaling and function, as well as potential pathophysiological implications of naturally occurring mutations in this receptor identified in humans with reproductive disorders.

Genetic coregulation of age of female sexual maturation and lifespan through circulating IGF1 among inbred mouse strains

We previously reported that mouse strains with lower circulating insulin-like growth factor 1 (IGF1) level at 6 mo have significantly extended longevity. Here we report that strains with lower IGF1 have significantly delayed age of female sexual maturation, measured by vaginal patency (VP). Among strains with normal lifespans (mean lifespan >600 d), delayed age of VP associated with greater longevity (P = 0.015), suggesting a genetically regulated tradeoff at least partly mediated by IGF1. Supporting this hypothesis, C57BL/6J females had 9% lower IGF1, 6% delayed age of VP, and 24% extended lifespan compared with C57BL/6J.C3H/HeJ-Igf1, which carries a C3H/HeJ allele on chromosome (Chr) 10 that increases IGF1. To identify genetic loci/genes that regulate female sexual maturation, including loci that mediate lifespan tradeoffs, we performed haplotype association mapping for age of VP and identified significant loci on Chrs 4 (Vpq1) and 16 (Vpq2 and 3). At each locus, wild-derived strains share a unique haplotype that associates with delayed VP. Substitution of Chr 16 of C57BL/6J with Chr 16 from a wild-derived strain significantly reduced IGF1 and delayed VP. Strains with a wild-derived allele at Vpq3 have significantly extended longevity compared with strains with other alleles. Bioinformatic analysis identified Nrip1 at Vpq3 as a candidate gene. Nrip1(-/-) females have significantly reduced IGF1 and delayed age of VP compared with Nrip1(+/+) females. We conclude that IGF1 may coregulate female sexual maturation and longevity; wild-derived strains carry specific alleles that delay sexual maturation; and Nrip1 is involved in regulating sexual maturation and may affect longevity by regulating IGF1 level.

A potential mechanism for the sexual dimorphism in the onset of puberty and incidence of idiopathic central precocious puberty in children: sex-specific kisspeptin as an integrator of puberty signals

The major determinants of the variability in pubertal maturation are reported to be genetic and inherited. Nonetheless, nutritional status contributes significantly to this variability. Malnutrition delays puberty whereas obesity has been associated to a rise in Idiopathic Central Precocious Puberty (ICPP) in girls. However, epidemiology data indicate that contribution of obesity to early puberty varies significantly among ethnic groups, and that obesity-independent inheritable genetic factors are the strongest predictors of early puberty in any ethnic group. In fact, two human mutations with confirmed association to ICPP have been identified in children with no history of obesity. These mutations are in kisspeptin and kisspeptin receptor, a ligand/receptor pair with a major role on the onset of puberty and female cyclicity after puberty. Progressive increases in kisspeptin expression in hypothalamic nuclei known to regulate reproductive function has been associated to the onset of puberty, and hypothalamic expression of kisspeptin is reported to be sexually dimorphic in many species, which include humans. The hypothalamus of females is programmed to express significantly higher levels of kisspeptin than their male counterparts. Interestingly, incidence of ICPP and delayed puberty in children is markedly sexually dimorphic, such that ICPP is at least 10-fold more frequent in females, whereas prevalence of delayed puberty is about 5-fold higher in males. These observations are consistent with a possible involvement of sexually dimorphic kisspeptin signaling in the sexual dimorphism of normal puberty and of pubertal disorders in children of all ethnicities. This review discusses the likelihood of such associations, as well as a potential role of kisspeptin as the converging target of environmental, metabolic, and hormonal signals, which would be integrated in order to optimize reproductive function.

Genetic studies on the ghrelin, growth hormone secretagogue receptor (GHSR) and ghrelin O-acyl transferase (GOAT) genes

Ghrelin is a 28 amino acid peptide hormone that is produced both centrally and peripherally. Regulated by the ghrelin O-acyl transferase enzyme, ghrelin exerts its action through the growth hormone secretagogue receptor, and is implicated in a diverse range of physiological processes. These implications have placed the ghrelin signaling pathway at the center of a large number of candidate gene and genome-wide studies which aim to identify the genetic basis of human heterogeneity. In this review we summarize the available data on the genetic variability of ghrelin, its receptor and its regulatory enzyme, and their association with obesity, stature, type 2 diabetes, cardiovascular disease, eating disorders, and reward seeking behavior.

New genetic factors implicated in human GnRH-dependent precocious puberty: the role of kisspeptin system

Human puberty is triggered by the reemergence of GnRH pulsatile secretion with progressive activation of the gonadal function. A number of genes have been identified in the complex regulatory neuroendocrine network that controls puberty initiation. KISS1 and KISS1R genes, which encode kisspeptin and its cognate receptor, respectively, are considered crucial factors for acquisition of normal reproductive function. Recently, rare missense mutations and single nucleotide polymorphisms (SNPs) of the kisspeptin system were associated with puberty onset. Two gain-of-function mutations of the KISS1 and KISS1R genes were implicated in the pathogenesis of GnRH-dependent precocious puberty, previously considered idiopathic. These discoveries have yielded significant insights into the physiology and pathophysiology of this important life transition time. Here, we review the current molecular defects that are implicated in human GnRH-dependent precocious puberty.

KISS1R intracellular trafficking and degradation: effect of the Arg386Pro disease-associated mutation

The goal of this study was to investigate how the Arg386Pro mutation prolongs KiSS-1 receptor (KISS1R) responsiveness to kisspeptin, contributing to human central precocious puberty. Confocal imaging showed colocalization of wild-type (WT) KISS1R with a membrane marker, which persisted for up to 5 h of stimulation. Conversely, no colocalization with a lysosome marker was detected. Also, overnight treatment with a lysosome inhibitor did not affect WT KISS1R protein, whereas overnight treatment with a proteasome inhibitor increased protein levels by 24-fold. WT and Arg386Pro KISS1R showed time-dependent internalization upon stimulation. However, both receptors were recycled back to the membrane. The Arg386Pro mutation did not affect the relative distribution of KISS1R in membrane and internalized fractions when compared to WT KISS1R for up to 120 min of stimulation, demonstrating that this mutation does not affect KISS1R trafficking rate. Nonetheless, total Arg386Pro KISS1R was substantially increased compared with WT after 120 min of kisspeptin stimulation. This net increase was eliminated by blockade of detection of recycled receptors, demonstrating that recycled receptors account for the increased responsiveness of this mutant to kisspeptin. We therefore conclude the following: 1) WT KISS1R is degraded by proteasomes rather than lysosomes; 2) WT and Arg386Pro KISS1R are internalized upon stimulation, but most of the internalized receptors are recycled back to the membrane rather than degraded; 3) the Arg386Pro mutation does not affect the rate of KISS1R trafficking--instead, it prolongs responsiveness to kisspeptin by decreasing KISS1R degradation, resulting in the net increase on mutant receptor recycled back to the plasma membrane.