Digenic Origin of Difference of Sex Development in a Patient Harbouring DHX37 and MAMLD1 Variants

Background

The diagnostic process for identifying variations in sex development (DSD) remains challenging due to the limited availability of evidence pertaining to the association between phenotype and genotype. DSD incidence is reported as 2 in 10,000 births, and the etiology has been attributed to genetic causes. Case Presentation. The present study investigated genetic causes implicated in a case of a 15-year-old 46, XY patient, raised as a girl. Genetic analysis by clinical exome sequencing (CES) showed a digenic inheritance due to two known pathogenic mutations in the DHX37 gene and the MAMLD1 gene, while we excluded variants with pathogenic significance in 209 DSD-related genes.

Conclusions

Based on our literature review, this is the first case with the combined presence of pathogenic mutations in the MAMLD1 gene and DHX37 gene in a patient with gonadal dysgenesis.

A novel MAMLD1 variant in a newborn with hypospadias and elevated 17-hydroxyprogesterone

PURPOSE

Disorders of sex development (DSD) have complex pathogenesis, and evidence suggests an association between MAMLD1 defects and DSD. MAMLD1 is expressed in gonadal tissues and affected males exhibit hypospadias, steroid hormone abnormalities, or gonadal underdevelopment. We performed genetic testing on a newborn patient with severe hypospadias and an elevation of 17-hydroxyprogesterone (17α-OH) for the diagnosis of DSD.

METHODS

Genetic testing of the proband and parents was conducted using whole-exome and Sanger sequencing. The identified variant was transfected into HEK293T cells to assess mutant protein expression using western blot (WB) and into steroidogenic NCI-H295R cells to assess MAMLD1 and CYP17A1 transcript levels using qPCR. Molecular dynamics simulations were performed to construct a structural model and analyze potential biological implications.

RESULTS

A novel heterozygous variant was identified in the proband's MAMLD1, NM_005491.5: c.1619_1637del (p.Gln540Alafs*72), inherited from the mother. In transfected cells, the wild-type and mutant proteins were 86.2 and 68.3 kDa, respectively, indicating the formation of a truncated protein. While MAMLD1 transcription was not affected, CYP17A1 transcription levels decreased with the variant compared to wild-type, suggesting an impact on the transactivation of CYP17A1. The truncated protein exhibited enhanced hydrophobicity, owing to the absence of the C-terminal structural portion, resulting in a looser protein structure.

CONCLUSION

Severe hypospadias in the proband may be attributed to a novel MAMLD1 variant, whereas the 17α-OH elevation might be related to interference with CYP17A1 transcriptional activation. This study expands the spectrum of MAMLD1 variants and underscores the critical role of genetic testing in the diagnosis of DSD.

A New MAMLD1 Variant in an Infant With Microphallus and Hypospadias With Hormonal Pattern Suggesting Partial Hypogonadotropic Hypogonadism-Case Report

MAMLD1 (X chromosome) is one of the recognized genes related to different sex development. It is expressed in testis and ovaries and seems to be involved in fetal sex development and in adult reproductive function, including testosterone biosynthesis. However, its exact role remains unclear. Over 40 genetic variants have been described, mainly in male individuals and mostly associated with hypospadias. Although MAMLD1 has been shown to regulate the expression of the steroidogenic pathway, patients with MAMLD1 variants mostly show normal gonadal function and normal testosterone levels. Here we describe a patient (46,XY) with hypospadias and microphallus, with low testosterone and dihydrotestosterone (DHT) levels, and with inappropriately low values of luteinizing hormone (LH) during minipuberty. This hormonal pattern was suggestive of partial hypogonadotropic hypogonadism. A stimulation test with hCG (4 months) showed no significant increase in both testosterone and dihydrotestosterone concentrations. At 5 months of age, he was treated with intramuscular testosterone, and the penis length increased to 3.5 cm. The treatment was stopped at 6 months of age. Our gonadal function massive-sequencing panel detected a previously unreported nonsense variant in the MAMLD1 gene (c.1738C>T:p.Gln580Ter), which was classified as pathogenic. This MAMLD1 variant, predicting a truncated protein, could explain his genital phenotype. His hormonal profile (low testosterone, dihydrotestosterone, and LH concentrations) together with no significant increase of testosterone and DHT plasma concentrations (hCG test) highlight the potential role of this gene in the biosynthesis of testosterone during the fetal stage and minipuberty of the infant. Besides this, the LH values may suggest an involvement of MAMLD1 in the LH axis or a possible oligogenesis. It is the first time that a decrease in DHT has been described in a patient with an abnormal MAMLD1.

MAMLD1 and Differences/Disorders of Sex Development: An Update

MAMLD1 (alias CXorf6) was first documented in 2006 as a causative gene of 46,XY differences/disorders of sex development (DSD). MAMLD1/Mamld1 is expressed in the fetal testis and is predicted to enhance the expression of several Leydig cell-specific genes. To date, hemizygous MAMLD1 variants have been identified in multiple 46,XY individuals with hypomasculinized external genitalia. Pathogenic MAMLD1 variants are likely to cause genital abnormalities at birth and are possibly associated with age-dependent deterioration of testicular function. In addition, some MAMLD1 variants have been identified in 46,XX individuals with ovarian dysfunction. However, recent studies have raised the possibility that MAMLD1 variants cause 46,XY DSD and ovarian dysfunction as oligogenic disorders. Unsolved issues regarding MAMLD1 include the association between MAMLD1 variants and 46,XX testicular DSD, gene-gene interactions in the development of MAMLD1-mediated DSD, and intracellular functions of MAMLD1.

Oligogenic Causes of Human Differences of Sex Development: Facing the Challenge of Genetic Complexity

BACKGROUND

Deviations of intrauterine sex determination and differentiation and postnatal sex development can result in a very heterogeneous group of differences of sex development (DSD) with a broad spectrum of phenotypes. Variants in genes involved in sexual development cause different types of DSD, but predicting the phenotype from an individual's genotype and vice versa remains challenging.

SUMMARY

Next Generation Sequencing (NGS) studies suggested that oligogenic inheritance contributes to the broad manifestation of DSD phenotypes. This review will focus on possible oligogenic inheritance in DSD identified by NGS studies with a special emphasis on NR5A1variants as an example of oligogenic origin associated with a broad range of DSD phenotypes. We thoroughly searched the literature for evidence regarding oligogenic inheritance in DSD diagnosis with NGS technology and describe the challenges to interpret contribution of these genes to DSD phenotypic variability and pathogenicity. Key Messages: Variants in common DSD genes like androgen receptor (AR), mitogen-activated protein kinase kinase kinase 1 (MAP3K1), Hydroxy-Delta-5-Steroid Dehydrogenase 3 Beta- And Steroid Delta-Isomerase 2 (HSD3B2), GATA Binding Protein 4 (GATA4), zinc finger protein friend of GATA family member 2 (ZFPM2), 17b-hydroxysteroid dehydrogenase type 3 (HSD17B3), mastermind-like domain-containing protein 1 (MAMLD1), and nuclear receptor subfamily 5 group A member 1 (NR5A1) have been detected in combination with additional variants in related genes in DSD patients with a broad range of phenotypes, implying a role of oligogenic inheritance in DSD, while still awaiting proof. Use of NGS approach for genetic diagnosis of DSD patients can reveal more complex genetic traits supporting the concept of oligogenic cause of DSD. However, assessing the pathomechanistic contribution of multiple gene variants on a DSD phenotype remains an unsolved conundrum.

Clinical and molecular spectrum of 46,XY disorders of sex development that harbour MAMLD1 variations: case series and review of literature

Background

Mastermind-like domain-containing 1 (MAMLD1) has previously been identified as a causative gene for “46,XY Disorders of Sex Development (DSD)”. Recently, there has been some controversy regarding the causative role of MAMLD1 variations in DSDs. Here we describe a clinical series and review the reported cases to evaluate the role of MAMLD1 variants in children with 46,XY DSD. Cases of 46,XY DSD harbouring MAMLD1 variants from unrelated families were recruited from the Beijing Children’s Hospital in China (N = 10) or identified through a literature search (N = 26). The clinical manifestations and genetic variants of all the patients were evaluated.

Results

Hypospadias was the most prevalent phenotype among our 10 cases (8 out of 10 cases) and in all the previously reported ones. Central precocious puberty and isolated micropenis were observed for the first time. Among the 10 cases, nine variants were identified, including three nonsense (p.R356X, p.Q152X, and p.Q124X) and six missense (p.P334S, p.S662R, p.A421P,p.T992I, p.P542S, and p.R927L) variants. In silico analysis showed that the variants p.P334S, p.P542S, p.S662R, and p.R927Lmight lead to drastic changes in the interaction force of the amino acid chain and the flexibility of the spatial structure, and such changes may affect protein function.

Conclusion

Patients with 46,XY DSD harbouring MAMLD1variants manifest a broad spectrum of phenotypes and mostly present with hypospadias. The six novel variants reported here enrich the mutation database and contribute to our understanding of the pathogenesis of 46,XY DSD.

Disorders of Sex Development in Individuals Harbouring MAMLD1 Variants: WES and Interactome Evidence of Oligogenic Inheritance

Mastermind-like domain-containing 1 (MAMLD1) has been shown to play an important role in the process of sexual development and is associated with 46,XY disorders of sex development (DSDs). However, the causative role of MAMLD1 variations in DSDs remains disputable. In this study, we have described a clinical series on children from unrelated families with 46,XY DSD harbouring MAMLD1 variants. Whole exome sequencing (WES) was performed for each patient. WES data were filtered using common tools and disease customisation algorithms, including comparison against lists of known and candidate MAMLD1-related and DSD-related genes. Lastly, we investigated the hypothesis that MAMLD1-related DSD may follow an oligogenic mode of inheritance. Forty-three potentially deleterious/candidate variants of 18 genes (RET, CDH23, MYO7A, NOTCH2, MAML1, MAML2, CYP1A1, WNT9B, GLI2, GLI3, MAML3, WNT9A, FRAS1, PIK3R3, FREM2, PTPN11, EVC, and FLNA) were identified, which may have contributed to the patient phenotypes. MYO7A was the most commonly identified gene. Specific gene combinations were also identified. In the interactome analysis, MAMLD1 exhibited direct connection with MAML1/2/3 and NOTCH1/2. Through NOTCH1/2, the following eight genes were shown to be associated with MAMLD1:WNT9A/9B, GLI2/3, RET, FLNA, PTPN11, and EYA1. Our findings provide further evidence that individuals with MAMLD1-related 46,XY DSD could carry two or more variants of known DSD-related genes, and the phenotypic outcome of affected individuals might be determined by multiple genes.

CBX2-dependent transcriptional landscape: implications for human sex development and its defects

Sex development, a complex and indispensable process in all vertebrates, has still not been completely elucidated, although new genes involved in sex development are constantly being discovered and characterized. Chromobox Homolog 2 (CBX2) is one of these new additions and has been identified through a 46,XY girl with double heterozygous variants on CBX2.1, causing Differences of Sex Development (DSD). The mutated CBX2.1 failed to adequately regulate downstream targets important for sex development in humans, specifically steroidogenic factor 1 (NR5A1/SF1). To better place CBX2.1 in the human sex developmental cascade, we performed siRNA and CBX2.1 overexpression experiments and created a complete CRISPR/Cas9-CBX2 knockout in Sertoli-like cells. Furthermore, we deployed Next Generation Sequencing techniques, RNA-Sequencing and DamID-Sequencing, to identify new potential CBX2.1 downstream genes. The combination of these two next generation techniques enabled us to identify genes that are both bound and regulated by CBX2.1. This allowed us not only to expand our current knowledge about the influence of CBX2.1 in human sex development, but also to advance our insight in the mechanisms governing one of the most important decisions during embryonal development, the commitment to either female or male gonads.

Broad Phenotypes of Disorders/Differences of Sex Development in MAMLD1 Patients Through Oligogenic Disease

Disorders/differences of sex development (DSD) are the result of a discordance between chromosomal, gonadal, and genital sex. DSD may be due to mutations in any of the genes involved in sex determination and development in general, as well as gonadal and/or genital development specifically. MAMLD1 is one of the recognized DSD genes. However, its role is controversial as some MAMLD1 variants are present in normal individuals, several MAMLD1 mutations have wild-type activity in functional studies, and the Mamld1-knockout male mouse presents with normal genitalia and reproduction. We previously tested nine MAMLD1 variants detected in nine 46,XY DSD patients with broad phenotypes for their functional activity, but none of the mutants, except truncated L210X, had diminished transcriptional activity on known target promoters CYP17A1 and HES3. In addition, protein expression of MAMLD1 variants was similar to wild-type, except for the truncated L210X. We hypothesized that MAMLD1 variants may not be sufficient to explain the phenotype in 46,XY DSD individuals, and that further genetic studies should be performed to search for additional hits explaining the broad phenotypes. We therefore performed whole exome sequencing (WES) in seven of these 46,XY patients with DSD and in one 46,XX patient with ovarian insufficiency, who all carried MAMLD1 variants. WES data were filtered by an algorithm including disease-tailored lists of MAMLD1-related and DSD-related genes. Fifty-five potentially deleterious variants in 41 genes were identified; 16/55 variants were reported in genes in association with hypospadias, 8/55 with cryptorchidism, 5/55 with micropenis, and 13/55 were described in relation with female sex development. Patients carried 1-16 variants in 1-16 genes together with their MAMLD1 variation. Network analysis of the identified genes revealed that 23 genes presented gene/protein interactions with MAMLD1. Thus, our study shows that the broad phenotypes of individual DSD might involve multiple genetic variations contributing towards the complex network of sexual development.

Testis Development

Production of sperm and androgens is the main function of the testis. This depends on normal development of both testicular somatic cells and germ cells. A genetic program initiated from the Y chromosome gene sex-determining region Y (SRY) directs somatic cell specification to Sertoli cells that orchestrate further development. They first guide fetal germ cell differentiation toward spermatogenic destiny and then take care of the full service to spermatogenic cells during spermatogenesis. The number of Sertoli cells sets the limits of sperm production. Leydig cells secrete androgens that determine masculine development. Testis development does not depend on germ cells; that is, testicular somatic cells also develop in the absence of germ cells, and the testis can produce testosterone normally to induce full masculinization in these men. In contrast, spermatogenic cell development is totally dependent on somatic cells. We herein review germ cell differentiation from primordial germ cells to spermatogonia and development of the supporting somatic cells. Testicular descent to scrota is necessary for normal spermatogenesis, and cryptorchidism is the most common male birth defect. This is a mild form of a disorder of sex differentiation. Multiple genetic reasons for more severe forms of disorders of sex differentiation have been revealed during the last decades, and these are described along with the description of molecular regulation of testis development.

Attenuation of MAMLD1 Expression Suppresses the Growth and Migratory Properties of Gonadotroph Pituitary Adenomas

Gonadotroph pituitary adenomas (GPAs) constitute approximately 15-40% of pituitary tumors. Some GPAs can be highly infiltrative, making full surgical resection challenging and increasing the risk of recurrence. The transcriptional co-activator Mastermind-Like Domain Containing 1 (MAMLD1, CXorf6, F18) is involved in regulating signaling pathways important in pituitary tumorigenesis, including the Notch signaling pathway. However, MAMLD1's role in GPA remains unknown. GPA biopsies were collected from 96 patients following surgery, who were monitored until tumor recurrence. GPA tissue was used for immunohistochemistry. The murine GPA cell lines αT3 and LβT2 were used for in vitro experiments. Lentiviral constructs were employed for MAMLD1 knockdown (KD) and dominant negative (DN) mutant experiments. Quantitative real-time PCR (qPCR) and Western blotting of MAMLD1 and Notch2 were performed. MTT and Transwell assays were used to quantify proliferation and migration, respectively. An αT3 xenograft model was established in athymic nude mice followed by fluorescent IHC of xenograft tumors. MAMLD1 and Notch2 levels correlated positively with aggressive GPAs. Increased MAMLD1 levels correlated with shortened recurrence-free survival (RFS) in aggressive GPA patients. Moreover, MAMLD1 expression independently affected patient RFS according to multivariate Cox regression. In vitro, MAMLD1 KD in the murine GPA cell lines attenuated their proliferation and migration and Notch2 expression. Additionally, DN MAMLD1^L210X lowered their proliferative and migratory capacity. MAMLD1 KD suppressed tumor growth and Notch2 expression in murine xenografts. MAMLD1 may serve as a predictor of GPA patient outcome and may also be leveraged as a possible therapeutic target for aggressive GPA tumors.

Molecular genetics of hypospadias and cryptorchidism recent developments

During the last decade, a tremendous amount of work has been devoted to the study of the molecular genetics of isolated hypospadias and cryptorchidism, two minor forms of disorders of sex development (DSD). Beyond the genes involved in gonadal determination and sex differentiation, including those underlying androgen biosynthesis and signaling, new genes have been identified through genome-wide association study and familial clustering. Even if no single genetic defect can explain the whole spectrum of DSD, these recent studies reinforce the strong role of the genetic background in the occurrence of these defects. The timing of signaling disruption may explain the different phenotypes.

At the Crossroads of Fate-Somatic Cell Lineage Specification in the Fetal Gonad

The reproductive endocrine systems are vastly different between males and females. This sexual dimorphism of the endocrine milieu originates from sex-specific differentiation of the somatic cells in the gonads during fetal life. Most gonadal somatic cells arise from the adrenogonadal primordium. After separation of the adrenal and gonadal primordia, the gonadal somatic cells initiate sex-specific differentiation during gonadal sex determination with the specification of the supporting cell lineages: Sertoli cells in the testis vs granulosa cells in the ovary. The supporting cell lineages then facilitate the differentiation of the steroidogenic cell lineages, Leydig cells in the testis and theca cells in the ovary. Proper differentiation of these cell types defines the somatic cell environment that is essential for germ cell development, hormone production, and establishment of the reproductive tracts. Impairment of lineage specification and function of gonadal somatic cells can lead to disorders of sexual development (DSDs) in humans. Human DSDs and processes for gonadal development have been successfully modeled using genetically modified mouse models. In this review, we focus on the fate decision processes from the initial stage of formation of the adrenogonadal primordium in the embryo to the maintenance of the somatic cell identities in the gonads when they become fully differentiated in adulthood.

Human MAMLD1 Gene Variations Seem Not Sufficient to Explain a 46,XY DSD Phenotype

MAMLD1 is thought to cause disordered sex development in 46,XY patients. But its role is controversial because some MAMLD1 variants are also detected in normal individuals, several MAMLD1 mutations have wild-type activity in functional tests, and the male Mamld1-knockout mouse has normal genitalia and reproduction. Our aim was to search for MAMLD1 variations in 108 46,XY patients with disordered sex development, and to test them functionally. We detected MAMDL1 variations and compared SNP frequencies in controls and patients. We tested MAMLD1 transcriptional activity on promoters involved in sex development and assessed the effect of MAMLD1 on androgen production. MAMLD1 expression in normal steroid-producing tissues and mutant MAMLD1 protein expression were also assessed. Nine MAMLD1 mutations (7 novel) were characterized. In vitro, most MAMLD1 variants acted similarly to wild type. Only the L210X mutation showed loss of function in all tests. We detected no effect of wild-type or MAMLD1 variants on CYP17A1 enzyme activity in our cell experiments, and Western blots revealed no significant differences for MAMLD1 protein expression. MAMLD1 was expressed in human adult testes and adrenals. In conclusion, our data support the notion that MAMLD1 sequence variations may not suffice to explain the phenotype in carriers and that MAMLD1 may also have a role in adult life.