MYRF mutation leads to a single manifestation of sexual development and mimics partial androgen insensitivity syndrome: a case report and literature review.

OBJECTIVE: To highlight the challenges in diagnosing 46, XY disorder of sex development related to MYRF mutation. METHODS: We present an unusual case of a 12-year-old female child came for enlargement of clitoris and initially diagnosed as partial androgen insensitivity syndrome (AIS). RESULTS: On examination, the patient's vulva was found virilized with 3cm-long clitoris. Her peripheral blood karyotype was 46, XY. The ultrasound showed an empty pelvis and hormone results confirmed hyperandrogenism. Therefore, the partial AIS was suspected, but the following whole exon sequencing indicates a pathological missense mutation in MYRF. Further investigation and surgery did not reveal any brain, heart, lung or diaphragm lesions related to MYRF, but only maldeveloped internal genitalia and a persistent urachus. Her serum testosterone dropped to normal after surgical removal of the remaining ipsilateral testis and epididymitis without spermatogenesis as shown by pathology. CONCLUSION: Due to the karyotype, hyperandrogenism, empty pelvis but a virilism after puberty, the patient was initially diagnosed as partial AIS. This misleading clinical diagnose will not be verified as the MYRF mutation if without the whole exon sequencing, particularly in the absence of obvious brain, heart, lung and diaphragm lesions as in this case.

Clinical and genetic characteristics of a large international cohort of individuals with rare NR5A1/SF-1 variants of sex development.

BACKGROUND: Steroidogenic factor 1 (SF-1/NR5A1) is essential for human sex development. Heterozygous NR5A1/SF-1 variants manifest with a broad range of phenotypes of differences of sex development (DSD), which remain unexplained. METHODS: We conducted a retrospective analysis on the so far largest international cohort of individuals with NR5A1/SF-1 variants, identified through the I-DSD registry and a research network. FINDINGS: Among 197 individuals with NR5A1/SF-1 variants, we confirmed diverse phenotypes. Over 70% of 46, XY individuals had a severe DSD phenotype, while 90% of 46, XX individuals had female-typical sex development. Close to 100 different novel and known NR5A1/SF-1 variants were identified, without specific hot spots. Additionally, likely disease-associated variants in other genes were reported in 32 individuals out of 128 tested (25%), particularly in those with severe or opposite sex DSD phenotypes. Interestingly, 48% of these variants were found in known DSD or SF-1 interacting genes, but no frequent gene-clusters were identified. Sex registration at birth varied, with <10% undergoing reassignment. Gonadectomy was performed in 30% and genital surgery in 58%. Associated organ anomalies were observed in 27% of individuals with a DSD, mainly concerning the spleen. Intrafamilial phenotypes also varied considerably. INTERPRETATION: The observed phenotypic variability in individuals and families with NR5A1/SF-1 variants is large and remains unpredictable. It may often not be solely explained by the monogenic pathogenicity of the NR5A1/SF-1 variants but is likely influenced by additional genetic variants and as-yet-unknown factors. FUNDING: Swiss National Science Foundation (320030-197725) and Boveri Foundation Zürich, Switzerland.

In Tandem Intragenic Duplication of Doublesex and Mab-3-Related Transcription Factor 1 (DMRT1) in an SRY-Negative Boy with a 46,XX Disorder of Sex Development.

Disorders of sexual development (DSDs) encompass a group of congenital conditions associated with atypical development of internal and external genital structures. Among those with DSDs are 46,XX males, whose condition mainly arises due to the translocation of SRY onto an X chromosome or an autosome. In the few SRY-negative 46,XX males, overexpression of other pro-testis genes or failure of pro-ovarian/anti-testis genes may be involved, even if a non-negligible number of cases remain unexplained. A three-year-old boy with an SRY-negative 46,XX karyotype showed a normal male phenotype and normal prepubertal values for testicular hormones. A heterozygous de novo in tandem duplication of 50,221 bp, which encompassed exons 2 and 3 of the Doublesex and Mab-3-related transcription factor 1 (DMRT1) gene, was detected using MPLA, CGH-array analysis, and Sanger sequencing. Both breakpoints were in the intronic regions, and this duplication did not stop or shift the coding frame. Additional pathogenic or uncertain variants were not found in a known pro-testis/anti-ovary gene cascade using a custom NGS panel and whole genome sequencing. The duplication may have allowed DMRT1 to escape the transcriptional repression that normally occurs in 46,XX fetal gonads and thus permitted the testicular determination cascade to switch on. So far, no case of SRY-negative 46,XX DSD with alterations in DMRT1 has been described.

A Rare Case of Precocious Puberty in a Child with a Novel GATA-4 Gene Mutation: Implications for Disorders of Sex Development (DSD) and Review of the Literature.

BACKGROUND: Disorders/Differences of sex development (DSD) are often due to disruptions of the genetic programs that regulate gonad development. The GATA-4 gene, located on chromosome 8p23.1, encodes GATA-binding protein 4 (GATA-4), a transcription factor that is essential for cardiac and gonadal development and sexual differentiation. CASE DESCRIPTION: A child with a history of micropenis and cryptorchidism. At 8 years of age, he came under our observation for an increase in sexual pubic hair (pubarche). The laboratory parameters and the GnRH test suggested a central precocious puberty (CPP). Treatment with GnRH analogs was started, and we decided to perform genetic tests for DSD. The NGS genetic investigation showed a novel and heterozygous variant in the GATA-4 gene. DISCUSSION: In the literature, 26 cases with 46,XY DSD due to the GATA4 gene were reported. CONCLUSION: The novel variant in the GATA-4 gene of our patient was not previously associated with DSD. This is the first case of a DSD due to a GATA-4 mutation that develops precocious puberty. Precocious puberty could be associated with DSD and considered a prelude to hypogonadism in some cases.

Induced pluripotent stem cell line generated from a patient with differences in sex development (DSD) and multiple genetic variants including a large deletion in NR5A1.

The nuclear receptor subfamily 5, Group A, Member 1 (NR5A1) gene encodes steroidogenic factor 1 (SF1), which is necessary for development of steroid hormone-producing tissues including the gonad and adrenal gland. An induced pluripotent stem cell line (iPSC) LCHi002-B was generated from a participant with differences (disorders) of sex development (DSD) and multiple genetic variants including a large deletion in NR5A1, and three single nucleotide changes in DYNC2H1, PDE4D, and ZFPM2. The line presented typical morphology, expressed stem cell markers, differentiated into three germ layers, had normal karyotype, was mycoplasma-free, and carried mutations in NR5A1, DYNC2H1, PDE4D, and ZFPM2.

Bioinformatics analysis and verification of hub genes in 46,XY, disorders of sexual development.

CONTEXT: 46,XY, disorders of sexual development (46,XY, DSD) is a congenital genetic disease whose pathogenesis is complex and clinical manifestations are diverse. The existing molecular research has often focused on single-centre sequencing data, instead of prediction based on big data. AIMS: This work aimed to fully understand the pathogenesis of 46,XY, DSD, and summarise the key pathogenic genes. METHODS: Firstly, the potential pathogenic genes were identified from public data. Secondly, bioinformatics was used to predict pathogenic genes, including hub gene analysis, protein-protein interaction (PPI) and function enrichment analysis. Lastly, the genomic DNA from two unrelated families were recruited, next-generation sequencing and Sanger sequencing were performed to verify the hub genes. KEY RESULTS: A total of 161 potential pathogenic genes were selected from MGI and PubMed gene sets. The PPI network was built which included 144 nodes and 194 edges. MCODE 4 was selected from PPI which scored the most significant P -value. The top 15 hub genes were ranked and identified by Cytoscape. Furthermore, three variants were found on SRD5A2 gene by genome sequencing, which belonged to the prediction hub genes. CONCLUSIONS: Our results indicate that occurrence of 46,XY, DSD is attributed to a variety of genes. Bioinformatics analysis can help us predict the hub genes and find the most core network MCODE model. IMPLICATIONS: Bioinformatic predictions may provide a novel perspective on better understanding the pathogenesis of 46,XY, DSD.

Regulators of male and female sexual development are critical for the transmission of a malaria parasite.

Malaria transmission to mosquitoes requires a developmental switch in asexually dividing blood-stage parasites to sexual reproduction. In Plasmodium berghei, the transcription factor AP2-G is required and sufficient for this switch, but how a particular sex is determined in a haploid parasite remains unknown. Using a global screen of barcoded mutants, we here identify genes essential for the formation of either male or female sexual forms and validate their importance for transmission. High-resolution single-cell transcriptomics of ten mutant parasites portrays the developmental bifurcation and reveals a regulatory cascade of putative gene functions in the determination and subsequent differentiation of each sex. A male-determining gene with a LOTUS/OST-HTH domain as well as the protein interactors of a female-determining zinc-finger protein indicate that germ-granule-like ribonucleoprotein complexes complement transcriptional processes in the regulation of both male and female development of a malaria parasite.

Additional evidence for the role of chromosomal imbalances and SOX8, ZNRF3 and HHAT gene variants in early human testis development.

BACKGROUND: Forty-six ,XY Differences/Disorders of Sex Development (DSD) are characterized by a broad phenotypic spectrum ranging from typical female to male with undervirilized external genitalia, or more rarely testicular regression with a typical male phenotype. Despite progress in the genetic diagnosis of DSD, most 46,XY DSD cases remain idiopathic. METHODS: To determine the genetic causes of 46,XY DSD, we studied 165 patients of Tunisian ancestry, who presented a wide range of DSD phenotypes. Karyotyping, candidate gene sequencing, and whole-exome sequencing (WES) were performed. RESULTS: Cytogenetic abnormalities, including a high frequency of sex chromosomal anomalies (85.4%), explained the phenotype in 30.9% (51/165) of the cohort. Sanger sequencing of candidate genes identified a novel pathogenic variant in the SRY gene in a patient with 46,XY gonadal dysgenesis. An exome screen of a sub-group of 44 patients with 46,XY DSD revealed pathogenic or likely pathogenic variants in 38.6% (17/44) of patients. CONCLUSION: Rare or novel pathogenic variants were identified in the AR, SRD5A2, ZNRF3, SOX8, SOX9 and HHAT genes. Overall our data indicate a genetic diagnosis rate of 41.2% (68/165) in the group of 46,XY DSD.

Ovotesticular Difference of Sex Development: Genetic Background, Histological Features, and Clinical Management.

BACKGROUND: Ovotesticular disorder/difference of sex development (DSD) refers to the co-presence of testicular and ovarian tissue in one individual. Childhood management is challenging as there are many uncertainties regarding etiology, gonadal function, and gender outcome. SUMMARY: Ovotesticular DSD should mainly be considered in 46,XX children with atypical genitalia and normal adrenal steroid profiles. Various underlying genetic mechanisms have been described. Histological assessment of ovotestes requires expert revision and has many pitfalls. Neonatal sex assignment is essential, but as gender outcome is unpredictable, this should be regarded as provisional until a stable gender identity has developed. Therefore, it is crucial not to perform any irreversible medical or surgical procedure in affected individuals until adolescents can give their full informed consent. Gonadal function mostly allows for spontaneous pubertal development; however, fertility is compromised, especially in boys. Specific long-term outcome data for ovotesticular DSD are lacking but can be extrapolated from studies in other DSD populations. KEY MESSAGES: Management of ovotesticular DSD has changed in recent years, prioritizing the child's future right for autonomy and self-determination. The benefits and pitfalls of this new approach have not been documented yet and require intensive monitoring on an international scale.

Establishing a Molecular Genetic Diagnosis in Children with Differences of Sex Development: A Clinical Approach.

BACKGROUND: Despite distinct underlying aetiologies, the clinical phenotypes and hormonal profiles of children with various differences of sex development (DSD) are often similar, which presents challenges to ascertaining an accurate diagnosis on clinical grounds alone. Associated features and important clinical outcomes can, however, vary significantly in different DSD, thus establishing an accurate molecular diagnosis may have important implications for decision-making and management planning in a given individual. SUMMARY: The wider availability of next-generation sequencing techniques in recent years has led to recommendations for earlier integration of genetic testing in the diagnostic pathway of children with DSD. This review provides a practical overview of the clinical applications, advantages, and limitations of the more commonly available diagnostic genetic tests and outlines a suggested approach to testing. The potential clinical implications of a confirmed genetic diagnosis, subsequent management pathways for individuals with DSD, and challenges that remain to be addressed are also outlined. KEY MESSAGES: Despite significant improvements in our understanding of the complex genetic pathways that underlie DSD, an accurate diagnosis still eludes many affected individuals. Establishing a molecular diagnosis provides aetiological certainty, enabling improved information for families and individualized clinical management, including monitoring or prophylactic intervention where additional health risks exist. A stepwise approach to genomic testing is recommended to afford highest diagnostic yield from available resources. Looking forward, collaborative multicentre prospective studies will be required to assess the true impact of a genetic diagnosis on improving clinical care pathways and health, well-being and patient-reported outcomes for individuals with DSD.

The Long Path to Our Current Understanding Regarding Care of Children with Differences/Disorders of Sexual Development.

Testes were associated with maleness from antiquity, and ancient societies had fanciful myths about the origins of the sexes and about fetal sexual development. 17th century anatomists developed the concept that mammals developed from eggs and discovered sperm in semen; in 1878, Hertwig observed sperm entering eggs (of sea urchins), establishing the cellular basis of sex development. Individuals with atypical genitalia were known clinically in the 17th century, with much debate about their origins, but by the late 19th century it was generally accepted that gonads determined sex, and that sex determined gender role. Testosterone was isolated in 1935, and Alfred Jost showed that both circulating testosterone and diffusible anti-Mullerian hormone were needed for male development. Patients with apparent androgen insensitivity were reported in 1937 and shown to be unresponsive to exogenous androgen by Lawson Wilkins in 1957; androgen receptor mutations were reported in 1989. Steroidogenic errors were associated with differences in sex development (DSDs) starting in the 1940s, and finding mutations in the responsible enzymes explained many forms of hyper- and hypo-androgenism in both sexes. Sex chromosomes were identified in the early 20th century; Y was associated with maleness, and the responsible SRY gene was identified in 1991. Early efforts to manage patients with DSDs were confounded by philosophical perspectives on the relative roles of prenatal biology versus postnatal environment. Approaches to natal sex assignment evolved in the later 20th century and now emphasize a team approach based on data, not guessing, parental involvement, cultural considerations, and the acknowledgement of uncertainty.

Postnatal developmental expression of apelin receptor proteins and its role in juvenile mice testis.

The expression of apelin system has been shown in the adult testis of rat and mice. It has also been emphasized that regulation of testicular activity in early stages is important to sustain normal testicular activity in adulthood. Since the expression of apelin receptor (APJ) has been shown in the adult testis, moreover, developmental expression of APJ and its role has not been explored yet. Thus, we have examined the testicular expression of APJ during postnatal stages with special reference to proliferation, apoptosis and hormone secretion in early postnatal stage. Postnatal analysis showed that circulating apelin was lowest at PND1 and maximum at PND42. Among testosterone, estrogen and androstenedione, only circulating testosterone showed a gradual increase from PND1 to PND42. Testicular expression of APJ was also developmenatly regulated from PND1 to PND42, revealing a positive correlation with circulating apelin, testosterone, and androstenedione. Immunohistochemical study showed that APJ was mainly confined to Leydig cells of early postnatal stages, whereas, seminiferous tubules at PND42 showed immunostaining in the round spermatids. APJ inhibition from PND14-PND20 by ML221 suppressed the testicular proliferation, increased apoptosis and increased estrogen secretion. However, expression of AR was down-regulated by ML221 treatment. Furthermore, ML221 decreased the abundance of p-Akt. In vitro study also showed that APJ antagonist, ML221 decreased AR expression. These results suggests that apelin signaling during early developmental stages might be required to stimulate the germ cell proliferation, and inhibition of apoptosis. Both in vivo and in vitro study have shown that expression of AR was regulated by apelin signaling. Since the first wave spermatogenesis involves proliferation and apoptosis, therefore, further study would be required to unravel the exact mechanism of apelin mediated regulation of testicular activity during early postnatal stages. In conclusion, the present results are an indicative of apelin mediated signaling during early postnatal stage for regulation of germ cell proliferation, apoptosis and AR expression.

[Clinical and genetic analysis of a child with disorder of sex development].

OBJECTIVE: To report on the diagnosis and treatment process and clinical characteristics of a child with disorder of sex development (DSD) and to conduct pathological, imaging and genetic analysis for the patient. METHODS: Clinical data of the patient were collected. Genetic testing including chromosomal karyotyping, fluorescence in situ hybridization (FISH), copy number variations (CNVs) analysis, SRY gene detection and multiple ligation-dependent probe amplification (MLPA) were carried out. RESULTS: The patient had a social gender of male, with a history of hypospadia and breast development. Sex hormone tests showed slightly raised prolactin. Imaging results showed bilateral breast hyperplasia, abnormal seminal vesicle glands, rudimentary uterus, and underdeveloped right testis. Intraoperative examination revealed that the child had an ovary on the left and a testis on the right. The pathological results showed fibroadenomatoid changes in the breast. The patient had a karyotype of 46,XX. FISH results showed 46,XX.ish(DXZ1x2, SRYx0). Molecular testing showed that NR0B1, PHEX, CXORF21, GJB1, PQBP1, and COL4A5 genes are duplicated. There was a presence of SRY gene and absence of UYT gene. CONCLUSION: DSD should be considered in patients with genital abnormality and male breast development. Ultrasound, sex hormone test and genetic testing should be performed to confirm the diagnosis of DSD, and molecular testing should be performed if necessary. Individualized treatment of DSD patient requires cooperation of multiple clinical disciplines.

A male-specific doublesex isoform reveals an evolutionary pathway of sexual development via distinct alternative splicing mechanisms.

The doublesex/mab-3 related transcription factor (Dmrt) genes regulate sexual development in metazoans. Studies of the doublesex (dsx) gene in insects, in particular Drosophila melanogaster, reveal that alternative splicing of dsx generates sex-specific Dsx isoforms underlying sexual differentiation. Such a splicing-based mechanism underlying sex-specific Dmrt function is thought to be evolved from a transcription-based mechanism used in non-insect species, but how such transition occurs during evolution is not known. Here we identified a male-specific dsx transcript (dsxM2) through intron retention (IR), in addition to previously identified dsxM and dsxF transcripts through alternative polyadenylation (APA) with mutually exclusive exons. We found that DsxM2 had similarly masculinizing function as DsxM. We also found that the IR-based mechanism generating sex-specific dsx transcripts was conserved from flies to cockroaches. Further analysis of these dsx transcripts suggested an evolutionary pathway from sexually monomorphic to sex-specific dsx via the sequential use of IR-based and APA-based alternative splicing.

Can Non-Coding NR5A1 Gene Variants Explain Phenotypes of Disorders of Sex Development?

INTRODUCTION: NR5A1 is an essential transcription factor that regulates several target genes involved in reproduction and endocrine function. Pathogenic variants in this gene are responsible for a wide spectrum of disorders/differences of sex development (DSD). METHODS: The molecular study involved Sanger sequencing, in vitro assays, and whole exome sequencing (WES). RESULTS: Four variants were identified within the NR5A1 non-coding region in 3 patients with 46,XY DSD. In vitro analyses showed that promoter activity was affected in all cases. WES revealed variants in SRA1, WWOX, and WDR11 genes. DISCUSSION/CONCLUSION: Evaluation of clinical and phenotypic significance of variants located in a non-coding region of a gene can be complex, and little is known regarding their association with DSD. Nevertheless, based on the important region for interaction with cofactors essential to promote appropriated sex development and on our in vitro results, it is feasible to say that an impact on gene expression can be expected and that this may be correlated with the DSD pathophysiology presented in our patients. Considering the number of cases that remain elusive after screening for the well-known DSD related genes, we emphasize the importance of a careful molecular analysis of NR5A1 non-coding region which is commonly neglected and might explain some idiopathic DSD cases.

Secondary Metabolism Gene Clusters Exhibit Increasingly Dynamic and Differential Expression during Asexual Growth, Conidiation, and Sexual Development in Neurospora crassa.

Secondary metabolite clusters (SMCs) encode the machinery for fungal toxin production. However, understanding their function and analyzing their products requires investigation of the developmental and environmental conditions in which they are expressed. Gene expression is often restricted to specific and unexamined stages of the life cycle. Therefore, we applied comparative genomics analyses to identify SMCs in Neurospora crassa and analyzed extensive transcriptomic data spanning nine independent experiments from diverse developmental and environmental conditions to reveal their life cycle-specific gene expression patterns. We reported 20 SMCs comprising 177 genes-a manageable set for investigation of the roles of SMCs across the life cycle of the fungal model N. crassa-as well as gene sets coordinately expressed in 18 predicted SMCs during asexual and sexual growth under three nutritional and two temperature conditions. Divergent activity of SMCs between asexual and sexual development was reported. Of 126 SMC genes that we examined for knockout phenotypes, al-2 and al-3 exhibited phenotypes in asexual growth and conidiation, whereas os-5, poi-2, and pmd-1 exhibited phenotypes in sexual development. SMCs with annotated function in mating and crossing were actively regulated during the switch between asexual and sexual growth. Our discoveries call for attention to roles that SMCs may play in the regulatory switches controlling mode of development, as well as the ecological associations of those developmental stages that may influence expression of SMCs. IMPORTANCE Secondary metabolites (SMs) are low-molecular-weight compounds that often mediate interactions between fungi and their environments. Fungi enriched with SMs are of significant research interest to agriculture and medicine, especially from the aspects of pathogen ecology and environmental epidemiology. However, SM clusters (SMCs) that have been predicted by comparative genomics alone have typically been poorly defined and insufficiently functionally annotated. Therefore, we have investigated coordinate expression in SMCs in the model system N. crassa, and our results suggest that SMCs respond to environmental signals and to stress that are associated with development. This study examined SMC regulation at the level of RNA to integrate observations and knowledge of these genes in various growth and development conditions, supporting combining comparative genomics and inclusive transcriptomics to improve computational annotation of SMCs. Our findings call for detailed study of the function of SMCs during the asexual-sexual switch, a key, often-overlooked developmental stage.

DSDatlas: disorders of sex development atlas for reproductive endocrinology-related gene discovery in integrative omics platforms.

OBJECTIVE: To facilitate the identification of related genes and candidate biomarkers for disorders of sex development (DSD), we present disorders of sex development atlas (http://dsd.geneworks.cn). Disorders of sex development are a spectrum of endocrine diseases with distinct mutations of genes or chromosomes, but several issues regarding their pathogenesis remain elusive. High-throughput methods have allowed genomic and transcriptomic analyses of DSD; however, these data are deposited in various repositories owing to a lack of integrated online resources. DESIGN: A descriptive study of a specialized gene discovery platform designed for DSD. SETTING: Publicly available DSD omics datasets and self-produced datasets. PATIENT(S): None. INTERVENTION(S): None. MAIN OUTCOME MEASURE(S): The gene ranking result, with detailed information based on DSD terms in a gene-disease association knowledge base, and results of differential gene expression and mutation analyses from omics datasets. RESULT(S): The disorders of sex development atlas maintains both a knowledgebase for ranking DSD candidate genes and a database for DSD-related omics data analysis and visualization. We included 4 dominant classes of DSD in the knowledgebase: 15 subclasses and 44 specific disease names. Construction of the knowledgebase was centered upon Phenolyzer, with add-on seed gene databases customized by DSD-related genes collected from MalaCards, GeneCards, and DisGeNET. For the database, 25 experimental datasets related to DSD were integrated, including 24 public datasets from Gene Expression Omnibus and Sequence Read Archive and 1 self-generated dataset. A total of 474 samples from 240 DSD samples were collected for the database. CONCLUSION(S): This platform provides a friendly interface that integrates flexible and comprehensive analysis tools for differential expression and gene mutations between the DSD groups and controls.

The Use of Genetics for Reaching a Diagnosis in XY DSD.

Reaching a firm diagnosis is vital for the long-term management of a patient with a difference or disorder of sex development (DSD). This is especially the case in XY DSD where the diagnostic yield is particularly low. Molecular genetic technology is playing an increasingly important role in the diagnostic process, and it is highly likely that it will be used more often at an earlier stage in the diagnostic process. In many cases of DSD, the clinical utility of molecular genetics is unequivocally clear, but in many other cases there is a need for careful exploration of the benefit of genetic diagnosis through long-term monitoring of these cases. Furthermore, the incorporation of molecular genetics into the diagnostic process requires a careful appreciation of the strengths and weaknesses of the evolving technology, and the interpretation of the results requires a clear understanding of the wide range of conditions that are associated with DSD.

CBX2 in DSD: The Quirky Kid on the Block.

Sex development is an intricate and crucial process in all vertebrates that ensures the continued propagation of genetic diversity within a species, and ultimately their survival. Perturbations in this process can manifest as disorders/differences of sex development (DSD). Various transcriptional networks have been linked to development of the gonad into either male or female, which is actively driven by a set of genes that function in a juxtaposed manner and is maintained through the developmental stages to preserve the final sexual identity. One such identified gene is Chromobox homolog 2 (CBX2), an important ortholog of the Polycomb group (PcG) proteins, that functions as both chromatin modifier and highly dynamic transactivator. CBX2 was shown to be an essential factor for gonadal development in mammals, as genetic variants or loss-of-function of CBX2 can cause sex reversal in mice and humans. Here we will provide an overview of CBX2, its biological functions at molecular level, and the CBX2-dependent transcriptional landscape in gonadal development and DSD.

Genetics of 46,XY gonadal dysgenesis.

In 46,XY men, testis is determined by a genetic network(s) that both promotes testis formation and represses ovarian development. Disruption of this process results in a lack of testis-determination and affected individuals present with 46,XY gonadal dysgenesis (GD), a part of the spectrum of Disorders/Differences of Sex Development/Determination (DSD). A minority of all cases of GD are associated with pathogenic variants in key players of testis-determination, SRY, SOX9, MAP3K1 and NR5A1. However, most of the cases remain unexplained. Recently, unbiased exome sequencing approaches have revealed new genes and loci that may cause 46,XY GD. We critically evaluate the evidence to support causality of these factors and describe how functional studies are continuing to improve our understanding of genotype-phenotype relationships in genes that are established causes of GD. As genomic data continues to be generated from DSD cohorts, we propose several recommendations to help interpret the data and establish causality.