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Disorders of sex development (DSDs) are conditions affecting development of the gonads or genitalia. Variants in two key genes, SRY and its target SOX9 , are an established cause of 46,XY DSD, but the genetic basis of many DSDs remains unknown. SRY-mediated SOX9 upregulation in the early gonad is crucial for testis development, yet the regulatory elements underlying this have not been identified in humans. Here, we identified four DSD patients with overlapping duplications or deletions upstream of SOX9 . Bioinformatic analysis identified three putative enhancers for SOX9 that responded to different combinations of testis-specific regulators. All three enhancers showed synergistic activity and together drive SOX9 in the testis. This is the first study to identify SOX9 enhancers that, when duplicated or deleted, result in 46,XX or 46,XY sex reversal, respectively. These enhancers provide a hitherto missing link by which SRY activates SOX9 in humans, and establish SOX9 enhancer mutations as a significant cause of DSD. SRY and its target SOX9 are known key determinants in testis development. Here the authors by studying duplications and deletions upstream of SOX9 from patient samples with disorders of sex development (DSD) reveal enhancers for SOX9 critical for human sex development and DSD.

Sex development relies on the sex-specific action of gene networks to differentiate the bipotential gonads of the growing fetus into testis or ovaries, followed by the differentiation of internal and external genitalia depending on the presence or absence of hormones. Differences in sex development (DSD) arise from congenital alterations during any of these processes, and are classified depending on sex chromosomal constitution as sex chromosome DSD, 46,XY DSD or 46,XX DSD. Understanding the genetics and embryology of typical and atypical sex development is essential for diagnosing, treating and managing DSD. Advances have been made in understanding the genetic causes of DSD over the past 10 years, especially for 46,XY DSD. Additional information is required to better understand ovarian and female development and to identify further genetic causes of 46,XX DSD, besides congenital adrenal hyperplasia. Ongoing research is focused on the discovery of further genes related to typical and atypical sex development and, therefore, on improving diagnosis of DSD.In this Review, Reyes et al. provide an overview of the embryology and genetics of typical sex development, before discussing the clinical manifestations, genetic causes and phenotypic complexity of differences in sex development.

BackgroundThe early gonad is bipotential and can differentiate into either a testis or an ovary. In XY embryos, the SRY gene triggers testicular differentiation and subsequent male development via its action on a single gene, SOX9. The supporting cell lineage of the bipotential gonad will differentiate as testicular Sertoli cells if SOX9 is expressed and conversely will differentiate as ovarian granulosa cells when SOX9 expression is switched off.ResultsThrough copy number variation mapping this study identified duplications upstream of the SOX9 gene in three families with an isolated 46,XX disorder of sex development (DSD) and an overlapping deletion in one family with two probands with an isolated 46,XY DSD. The region of overlap between these genomic alterations, and previously reported deletions and duplications at the SOX9 locus associated with syndromic and isolated cases of 46,XX and 46,XY DSD, reveal a minimal non-coding 78 kb sex determining region located in a gene desert 517–595 kb upstream of the SOX9 promoter.ConclusionsThese data indicate that a non-coding regulatory region critical for gonadal SOX9 expression and subsequent normal sex development is located far upstream of the SOX9 promoter. Its copy number variations are the genetic basis of isolated 46,XX and 46,XY DSDs of variable severity (ranging from mild to complete sex reversal). It is proposed that this region contains a gonad specific SOX9 transcriptional enhancer(s), the gain or loss of which results in genomic imbalance sufficient to activate or inactivate SOX9 gonadal expression in a tissue specific manner, switch sex determination, and result in isolated DSD.

Objective To describe individuals with differences in sex development presenting with a female phenotype and an absent uterus and identify specific diagnostic characteristics that improve diagnostic accuracy and optimize patient care. Materials and Methods This descriptive comparative study included retrospective and prospective clinical data collected between 2023 and 2025 at the Reproductive Medicine Center “Universe,” Tbilisi, Georgia. Among 233 individuals evaluated for primary amenorrhea, 26% with a female phenotype and an absent uterus who were evaluated for Complete Androgen Insensitivity Syndrome, Mayer–Rokitansky–Küster–Hauser syndrome, and ovotesticular disorder of sex development were included in the final sample. All participants underwent clinical, hormonal, genetic, and imaging assessment. Laparoscopy and histomorphological examination were performed when indicated. Results Mayer–Rokitansky–Küster–Hauser syndrome accounted for 57.4%, Complete Androgen Insensitivity Syndrome for 37.7%, and ovotesticular disorder of sex development for 4.9% of the cases. Complete Androgen Insensitivity Syndrome patients exhibited preserved breast development with absent or sparse pubic hair, whereas Mayer–Rokitansky–Küster–Hauser syndrome and ovotesticular disorder of sex development patients exhibited normal pubic hair and breast development. Vaginal length was shortest in patients with Mayer–Rokitansky–Küster–Hauser, intermediate in those with complete androgen insensitivity syndrome, and variable in patients with ovotesticular disorder of sex development. Complete Androgen Insensitivity syndrome patients demonstrated male-range testosterone levels; Mayer–Rokitansky–Küster–Hauser patients exhibited female-range hormone profiles, and ovotesticular disorder of sex development patients were observed to have nonspecific endocrine patterns. Ovotesticular disorder of sex development was confirmed histomorphologically. Conclusion An integrated diagnostic approach combining specific clinical features, hormonal profiles, imaging, karyotyping, and histomorphology enables accurate differentiation of Mayer–Rokitansky–Küster–Hauser, complete androgen insensitivity syndrome, and ovotesticular disorder of sex development.

BackgroundMayer-Rokitansky-Küster-Hauser syndrome (MRKHS) is characterised by aplasia of the uterus, cervix and upper part of the vagina. The genetic aetiology remains incompletely understood.MethodsWe performed gene-level and gene set-level burden analyses based on exome sequencing/genome sequencing data from 727 probands with MRKHS and 2504 female control individuals. Single-cell RNA sequencing (scRNA-seq) was performed on human and mouse embryonic metanephros at different developmental stages. Genetic and transcriptomic data were integrated to prioritise suboptimal genetic signals, identify relevant cell types and determine key developmental stages. Potential digenic inheritance was assessed and prioritised using coexpression patterns from scRNA-seq data.ResultsWe identified known MRKHS genes (PAX8, BMP7, GREB1L) and novel candidates (PAN2, AGPAT2) with exome-wide significance. Enriched biological processes included cell apoptosis and mesenchymal-to-epithelial transition. In human embryos, MRKHS-associated genes were enriched in the uterine epithelium at eight gestational weeks (w8) and Wolffian duct epithelium at w11, supporting the biological relevance of burden signals. We detected 992 digenic combinations in MRKHS, with three achieving exome-wide significance (CPSF3L/CYP2A7, AICDA/NOS1, EVC2/KANK1).ConclusionOur study reveals both established and novel genetic contributors to MRKHS, links them to specific embryonic cell types and stages, and highlights potential digenic inheritance patterns. Integrating genetic burden and single-cell transcriptomic data provides new insights into the complex molecular mechanisms underlying MRKHS.

PurposeMayer–Rokitansky–Küster–Hauser (MRKH) syndrome consists of congenital absence of the uterus and vagina and is often associated with renal, skeletal, cardiac, and auditory defects. The genetic basis is largely unknown except for rare variants in several genes. Many candidate genes have been suggested by mouse models and human studies. The purpose of this study was to narrow down the number of candidate genes.MethodsWhole exome sequencing was performed on 111 unrelated individuals with MRKH; variant analysis focused on 72 genes suggested by mouse models, human studies of physiological candidates, or located near translocation breakpoints in t(3;16). Candidate variants (CV) predicted to be deleterious were confirmed by Sanger sequencing.ResultsSanger sequencing verified 54 heterozygous CV from genes identified through mouse (13 CV in 6 genes), human (22 CV in seven genes), and translocation breakpoint (19 CV in 11 genes) studies. Twelve patients had ≥ 2 CVs, including four patients with two variants in the same gene. One likely digenic combination of LAMC1 and MMP14 was identified.ConclusionWe narrowed 72 candidate genes to 10 genes that appear more likely implicated. These candidate genes will require further investigation to elucidate their role in the development of MRKH.

The term ‘differences of sex development’ (DSD) refers to a group of congenital conditions that are associated with atypical development of chromosomal, gonadal, or anatomical sex. Disorders of steroidogenesis comprise autosomal recessive conditions that affect adrenal and gonadal enzymes and are responsible for some conditions of 46,XX DSD where hyperandrogenism interferes with chromosomal and gonadal sex development. Congenital adrenal hyperplasias (CAHs) are disorders of steroidogenesis that mainly involve the adrenals (21-hydroxylase and 11-hydroxylase deficiencies) and sometimes the gonads (3-beta-hydroxysteroidodehydrogenase and P450-oxidoreductase); in contrast, aromatase deficiency mainly involves the steroidogenetic activity of the gonads. This review describes the main genetic, biochemical, and clinical features that apply to the abovementioned conditions. The activities of the steroidogenetic enzymes are modulated by post-translational modifications and cofactors, particularly electron-donating redox partners. The incidences of the rare forms of CAH vary with ethnicity and geography. The elucidation of the precise roles of these enzymes and cofactors has been significantly facilitated by the identification of the genetic bases of rare disorders of steroidogenesis. Understanding steroidogenesis is important to our comprehension of differences in sexual development and other processes that are related to human reproduction and fertility, particularly those that involve androgen excess as consequence of their impairment.

Infertility affects around 1 in 5 couples in the world. Congenital absence of the uterus results in absolute infertility in females. Müllerian agenesis is the nondevelopment of the uterus. Mayer–Rokitansky–Küster–Hauser (MRKH) syndrome is a condition of uterovaginal agenesis in the presence of normal ovaries and the 46 XX Karyotype. With advancements in reproductive techniques, women with MA having biological offspring is possible. The exact etiology of MA is unknown, although several genes and mechanisms affect the development of Müllerian ducts. Through this systematic review of the available literature, we searched for the genetic basis of MA. The aims included identification of the genes, chromosomal locations, changes responsible for MA, and fertility options, in order to offer proper management and counseling to these women with MA. A total of 85 studies were identified through searches. Most of the studies identified multiple genes at various locations, although the commonest involved chromosomes 1, 17, and 22. There is also conflicting evidence of the involvement of various candidate genes in the studies. The etiology of MA seems to be multifactorial and complex, involving multiple genes and mechanisms including various mutations and mosaicism.

Mutations in cytochrome P450 oxidoreductase (POR) cause a form of congenital adrenal hyperplasia (CAH). We report a novel R550W mutation in POR identified in a 46,XX patient with signs of aromatase deficiency. Analysis of aromatase deficiency from the R550W mutation in POR. Both the child and the mother had signs of virilization. Ultrasound revealed the presence of uterus and ovaries. No defects in CYP19A1 were found, but further analysis with a targeted Disorders of Sexual Development NGS panel (DSDSeq.V1, 111 genes) on a NextSeq (Illumina) platform in Madrid and Barcelona, Spain, revealed compound heterozygous mutations c.73_74delCT/p.L25FfsTer93 and c.1648C > T/p.R550W in POR. Wild-type and R550W POR were produced as recombinant proteins and tested with multiple cytochrome P450 enzymes at University Children's Hospital, Bern, Switzerland. POR-R550W showed 41% of the WT activity in cytochrome c and 7.7% activity for reduction of MTT. Assays of CYP19A1 showed a severe loss of activity, and CYP17A1 as well as CYP21A2 activities were also lost by more than 95%. Loss of CYP2C9, CYP2C19, and CYP3A4 activities was observed for the R550W-POR. Predicted adverse effect on aromatase activity as well as a reduction in binding of NADPH was confirmed. Pathological effects due to POR-R550W were identified, expanding the knowledge of molecular pathways associated with aromatase deficiency. Screening of the POR gene may provide a diagnosis in CAH without defects in genes for steroid metabolizing enzymes.

Duplications in the ~2 Mb desert region upstream of SOX9 at 17q24.3 may result in familial 46,XX disorders of sex development (DSD) without any effects on the XY background. A balanced translocation with its breakpoint falling within the same region has also been described in one XX DSD subject. We analyzed, by conventional and molecular cytogenetics, 19 novel SRY-negative unrelated 46,XX subjects both familial and sporadic, with isolated DSD. One of them had a de novo reciprocal t(11;17) translocation. Two cases carried partially overlapping 17q24.3 duplications ~500 kb upstream of SOX9, both inherited from their normal fathers. Breakpoints cloning showed that both duplications were in tandem, whereas the 17q in the reciprocal translocation was broken at ~800 kb upstream of SOX9, which is not only close to a previously described 46,XX DSD translocation, but also to translocations without any effects on the gonadal development. A further XX male, ascertained because of intellectual disability, carried a de novo cryptic duplication at Xq27.1, involving SOX3. CNVs involving SOX3 or its flanking regions have been reported in four XX DSD subjects. Collectively in our cohort of 19 novel cases of SRY-negative 46,XX DSD, the duplications upstream of SOX9 account for ~10.5% of the cases, and are responsible for the disease phenotype, even when inherited from a normal father. Translocations interrupting this region may also affect the gonadal development, possibly depending on the chromatin context of the recipient chromosome. SOX3 duplications may substitute SRY in some XX subjects.