X-Y chromosomal interchange in the aetiology of true hermaphroditism and of XX Klinefelter's syndrome

RNF212B E3 ligase is essential for crossover designation and maturation during male and female meiosis in the mouse

Meiosis, a reductional cell division, relies on precise initiation, maturation, and resolution of crossovers (COs) during prophase I to ensure the accurate segregation of homologous chromosomes during metaphase I. This process is regulated by the interplay of RING-E3 ligases such as RNF212 and HEI10 in mammals. In this study, we functionally characterized a recently identified RING-E3 ligase, RNF212B. RNF212B colocalizes and interacts with RNF212, forming foci along chromosomes from zygonema onward in a synapsis-dependent and DSB-independent manner. These consolidate into larger foci at maturing COs, colocalizing with HEI10, CNTD1, and MLH1 by late pachynema. Genetically, RNF212B foci formation depends on Rnf212 but not on Msh4, Hei10, and Cntd1, while the unloading of RNF212B at the end of pachynema is dependent on Hei10 and Cntd1. Mice lacking RNF212B, or expressing an inactive RNF212B protein, exhibit modest synapsis defects, a reduction in the localization of pro-CO factors (MSH4, TEX11, RPA, MZIP2) and absence of late CO-intermediates (MLH1). This loss of most COs by diakinesis results in mostly univalent chromosomes. Double mutants for Rnf212b and Rnf212 exhibit an identical phenotype to that of Rnf212b single mutants, while double heterozygous demonstrate a dosage-dependent reduction in CO number, indicating a functional interplay between paralogs. SUMOylome analysis of testes from Rnf212b mutants and pull-down analysis of Sumo- and Ubiquitin-tagged HeLa cells, suggest that RNF212B is an E3-ligase with Ubiquitin activity, serving as a crucial factor for CO maturation. Thus, RNF212 and RNF212B play vital, yet overlapping roles, in ensuring CO homeostasis through their distinct E3 ligase activities.

Evidence for high breakpoint variability in 46, XX, SRY-positive testicular disorder and frequent ARSE deletion that may be associated with short stature

BACKGROUND

The translocation of SRY onto one of the two X chromosomes results in a 46,XX testicular disorder of sex development; this is supposedly due to non-allelic homologous recombination between the protein kinase X gene (PRKX) and the inverted protein kinase Y pseudogene (PRKY). Although 46,XX SRY-positive men are infertile, the literature data indicate that some of these individuals are of short stature (relative to the general population). We sought to determine whether short stature was linked to additional, more complex chromosomal rearrangements.

METHODS

Twelve laboratories gathered detailed clinical, anthropomorphic, cytogenetic and genetic data (including chromosome microarray (CMA) data) on patients with 46,XX SRY-positive male syndrome.

RESULTS

SRY was present (suggesting a der(X)t(X;Y)) in 34 of the 38 cases (89.5%). When considering only the 20 patients with CMA data, we identified several chromosomal rearrangements and breakpoints - especially on the X chromosome. In the five cases for whom the X chromosome breakpoint was located in the pseudoautosomal (PAR) region, there was partial duplication of the derivate X chromosome. In contrast, in the 15 cases for whom the breakpoint was located downstream of the pseudoautosomal region, part of the derivate X chromosome had been deleted (included the arylsulfatase E (ARSE) gene in 11 patients). For patients with vs. without ARSE deletion, the mean height was respectively 167.7 ± 4.5 and 173.1 ± 4.0 cm; this difference was not statistically significant (p = 0.1005).

CONCLUSION

Although 46,XX SRY-positive male syndromes were mainly due to imbalanced crossover between the X and Y chromosome during meiosis, the breakpoints differed markedly from one patient to another (especially on the X chromosome); this suggests the presence of a replication-based mechanism for recombination between non-homologous sequences. In some patients, the translocation of SRY to the X chromosome was associated with ARSE gene deletion, which might have led to short stature. With a view to explaining this disorder of sex development, whole exome sequencing could be suggested for SRY-negative patients. This article is protected by copyright. All rights reserved.

Human cytogenetics at Johns Hopkins Hospital, 1959-1962

An account is given of the introduction of human cytogenetics to the Division of Medical Genetics at Johns Hopkins Hospital, and the first 3 years' work of the chromosome diagnostic laboratory that was established at the time. Research on human sex chromosome disorders, including novel discoveries in the Turner and Klinefelter syndromes, is described together with original observations on chromosome behavior at mitosis. It is written in celebration of the centenary of the birth of Victor McKusick, the acknowledged father of Medical Genetics, who established the Division and had the foresight to ensure that it included the investigation of human chromosomes.

A collection of XY female cell lines

Discordance between sexual phenotype and the 46,XY sex chromosome complement may be found in certain disorders of sexual development (DSD). Many of these DSD patients with female external genitalia and secondary sex characteristics have undescended testes and male internal genitalia. Causative mutations involving genes of the sex determining pathway, including the androgen receptor, SRY and the 5-alpha-reductase genes, are well-known, but the origin of other cases remain unresolved. In this report, we introduce our collection of lymphoblastoid lines derived from female patients with a 46,XY karyotype. These cell lines have been deposited and registered with the JCRB Cell Bank. They are available for comparison with other DSD cases and for further characterization of genetic loci involved in the mammalian sex determining pathway.

C14ORF39/SIX6OS1 is a constituent of the synaptonemal complex and is essential for mouse fertility

Meiotic recombination generates crossovers between homologous chromosomes that are essential for genome haploidization. The synaptonemal complex is a ‘zipper'-like protein assembly that synapses homologue pairs together and provides the structural framework for processing recombination sites into crossovers. Humans show individual differences in the number of crossovers generated across the genome. Recently, an anonymous gene variant in C14ORF39/SIX6OS1 was identified that influences the recombination rate in humans. Here we show that C14ORF39/SIX6OS1 encodes a component of the central element of the synaptonemal complex. Yeast two-hybrid analysis reveals that SIX6OS1 interacts with the well-established protein synaptonemal complex central element 1 (SYCE1). Mice lacking SIX6OS1 are defective in chromosome synapsis at meiotic prophase I, which provokes an arrest at the pachytene-like stage and results in infertility. In accordance with its role as a modifier of the human recombination rate, SIX6OS1 is essential for the appropriate processing of intermediate recombination nodules before crossover formation.

The synaptonemal complex is a meiosis-specific proteinaceous structure that supports homologous chromosome pairs during meiosis. Here, the authors show that SIX6OS1 (of previously unknown function) is part of the synaptonemal complex central element and upon deletion in mice, causes defective chromosome synapsis and infertility.

Involvement of FOXL2 and RSPO1 in Ovarian Determination, Development, and Maintenance in Mammals

In mammals, sex determination is a process through which the gonad is committed to differentiate into a testis or an ovary. This process relies on a delicate balance between genetic pathways that promote one fate and inhibit the other. Once the gonad is committed to the female pathway, ovarian differentiation begins and, depending on the species, is completed during gestation or shortly after birth. During this step, granulosa cell precursors, steroidogenic cells, and primordial germ cells start to express female-specific markers in a sex-dimorphic manner. The germ cells then arrest at prophase I of meiosis and, together with somatic cells, assemble into functional structures. This organization gives the ovary its definitive morphology and functionality during folliculogenesis. Until now, 2 main genetic cascades have been shown to be involved in female sex differentiation. The first is driven by FOXL2, a transcription factor that also plays a crucial role in folliculogenesis and ovarian fate maintenance in adults. The other operates through the WNT/CTNNB1 canonical pathway and is regulated primarily by R-spondin1. Here, we discuss the roles of FOXL2 and RSPO1/WNT/ CTNNB1 during ovarian development and homeostasis in different models, such as humans, goats, and rodents.

Sex Reversal in Non-Human Placental Mammals

Gonads are very peculiar organs given their bipotential competence. Indeed, early differentiating genital ridges evolve into either of 2 very distinct organs: the testis or the ovary. Accumulating evidence now demonstrates that both genetic pathways must repress the other in order for the organs to differentiate properly, meaning that if this repression is disrupted or attenuated, the other pathway may completely or partially be expressed, leading to disorders of sex development. Among these disorders are the cases of XY male-to-female and XX female-to-male sex reversals as well as true hermaphrodites, in which there is a discrepancy between the chromosomal and gonadal sex. Here, we review known cases of XY and XX sex reversals described in mammals, focusing mostly on domestic animals where sex reversal pathologies occur and on wild species in which deviations from the usual XX/XY system have been documented.

Evidence for Sex Chromosome Turnover in Proteid Salamanders

A major goal of genomic and reproductive biology is to understand the evolution of sex determination and sex chromosomes. Species of the 2 genera of the Salamander family Proteidae - Necturus of eastern North America, and Proteus of Southern Europe - have similar-looking karyotypes with the same chromosome number (2n = 38), which differentiates them from all other salamanders. However, Necturus possesses strongly heteromorphic X and Y sex chromosomes that Proteus lacks. Since the heteromorphic sex chromosomes of Necturus were detectable only with C-banding, we hypothesized that we could use C-banding to find sex chromosomes in Proteus. We examined mitotic material from colchicine-treated intestinal epithelium, and meiotic material from testes in specimens of Proteus, representing 3 genetically distinct populations in Slovenia. We compared these results with those from Necturus. We performed FISH to visualize telomeric sequences in meiotic bivalents. Our results provide evidence that Proteus represents an example of sex chromosome turnover in which a Necturus-like Y-chromosome has become permanently translocated to another chromosome converting heteromorphic sex chromosomes to homomorphic sex chromosomes. These results may be key to understanding some unusual aspects of demographics and reproductive biology of Proteus, and are discussed in the context of models of the evolution of sex chromosomes in amphibians.

Disorders of sex development: effect of molecular diagnostics

Disorders of sex development (DSDs) are a diverse group of conditions that can be challenging to diagnose accurately using standard phenotypic and biochemical approaches. Obtaining a specific diagnosis can be important for identifying potentially life-threatening associated disorders, as well as providing information to guide parents in deciding on the most appropriate management for their child. Within the past 5 years, advances in molecular methodologies have helped to identify several novel causes of DSDs; molecular tests to aid diagnosis and genetic counselling have now been adopted into clinical practice. Occasionally, genetic profiling of embryos prior to implantation as an adjunct to assisted reproduction, prenatal diagnosis of at-risk pregnancies and confirmatory testing of positive results found during newborn biochemical screening are performed. Of the available genetic tests, the candidate gene approach is the most popular. New high-throughput DNA analysis could enable a genetic diagnosis to be made when the aetiology is unknown or many differential diagnoses are possible. Nonetheless, concerns exist about the use of genetic tests. For instance, a diagnosis is not always possible even using new molecular approaches (which can be worrying for the parents) and incidental information obtained during the test might cause anxiety. Careful selection of the genetic test indicated for each condition remains important for good clinical practice. The purpose of this Review is to describe advances in molecular biological techniques for diagnosing DSDs.

Is 46XX karyotype always a female?

A19-year-old man, from a middle east country was referred by his physician to the endocrine department for bilateral gynaecomastia, low libido and sparse facial hair. There was no history of any chronic illness, mumps or traumatic injury to testis. He had clinical features suggestive of gonadotropin deficiency which was confirmed on biochemical testing. On karyotype and fluorescent in situ hybridisation analysis, he was found to have 46XX(SRY+) karyotype.

Chromosomal variants in klinefelter syndrome

Klinefelter syndrome (KS) describes the phenotype of the most common sex chromosome abnormality in humans and occurs in one of every 600 newborn males. The typical symptoms are a tall stature, narrow shoulders, broad hips, sparse body hair, gynecomastia, small testes, absent spermatogenesis, normal to moderately reduced Leydig cell function, increased secretion of follicle-stimulating hormone, androgen deficiency, and normal to slightly decreased verbal intelligence. Apart from that, amongst others, osteoporosis, varicose veins, thromboembolic disease, or diabetes mellitus are observed. Some of the typical features can be very weakly pronounced so that the affected men often receive the diagnosis only at the adulthood by their infertility. With a frequency of 4%, KS is described to be the most common genetic reason for male infertility. The most widespread karyotype in affected patients is 47,XXY. Apart from that, various other karyotypes have been described, including 46,XX in males, 47,XXY in females, 47,XX,der(Y), 47,X,der(X),Y, or other numeric sex chromosome abnormalities (48,XXXY, 48,XXYY, and 49,XXXXY). The focus of this review was to abstract the different phenotypes, which come about by the various karyotypes and to compare them to those with a 'normal' KS karyotype. For that the patients have been divided into 6 different groups: Klinefelter patients with an additional isochromosome Xq, with additional rearrangements on 1 of the 2 X chromosomes or accordingly on the Y chromosome, as well as XX males and true hermaphrodites, 47,XXY females and Klinefelter patients with other numeric sex chromosome abnormalities. In the latter, an almost linear increase in height and developmental delay was observed. Men with an additional isochromosome Xq show infertility and other minor features of 'normal' KS but not an increased height. Aside from the infertility, in male patients with other der(X) as well as der(Y) rearrangements and in XXY women no specific phenotype is recognizable amongst others due to the small number of cases. The phenotype of XX males depends on the presence of SRY (sex-determining region Y) and the level of X inactivation at which SRY-negative patients are generally rarely observed.

Genes and phenotypes of the human Y chromosome

By 1959 it was recognized that the gene (or genes) responsible for initiating the human male phenotype were carried on the Y chromosome. But in subsequent years, few phenotypes were associated with the Y chromosome. Recently, using molecular techniques combined with classical genetics, the Y chromosome has been the focus of intensive and productive investigation. Some of the findings are unexpected and have extended our understanding of the functions of the human Y chromosome. The notion that the Y chromosome is largely devoid of genes is changing. At the present, over 20 Y chromosome genes or pseudogenes have been identified or cloned, a number that is rapidly increasing. A high proportion of Y chromosome sequences have been found to be related to X chromosome sequences: the assembly of a complete physical map of the Y chromosome euchromatic region (believed to carry all of the genes) has shown 25% of the region studied to have homology to the X chromosome.3 Several X-homologous genes are located in the X and Y chromosome pairing regions, an area predicted to have shared homology. Surprisingly, some of the Y-encoded genes that lie outside of the X and Y pairing region share high sequence similarity, and in at least one case, functional identity, with genes on the X chromosome.

Genetic characterization of two 46,XX males without gonadal ambiguities

PURPOSE

To evaluate hypotheses which explain phenotypic variability in sex determining region Y positive 46,XX males. We investigate two 46,XX males without gonadal ambiguities.

METHODS

Cytogenetic and molecular analyses were used to identify the presence of Y chromosome material and to map the translocation breakpoint. Finally, the pattern of X chromosome inactivation was studied using the methylation assay at the androgen receptor locus.

RESULTS

The presence of Y chromosome material, including the sex determining region Y gene, was demonstrated in both men. However, the amount of translocated Y chromosome material differed between the patients. Different X chromosome inactivation patterns were found in the patients; random in one patient and non-random in the other.

CONCLUSIONS

We found a lack of association between phenotype and X chromosome inactivation pattern. Our cytogenetic and molecular analyses show support for the position effect hypothesis explaining the phenotypic variability in XX males.

Atypical XX male with the SRY gene located at the long arm of chromosome 1 and a 1qter microdeletion

Male individuals with a 46,XX karyotype have been designated as XX males. In 80% of the cases, the presence of Yp sequences, including the male sex-determining gene, SRY, has been demonstrated by molecular and/or fluorescence in situ hybridization (FISH) analyses. In most cases, Yp sequences are located on the short arm of the X chromosome, resulting from unequal recombination between Yp and Xp during paternal meiosis. Much less frequent in XX males is the localization of the SRY gene to an autosome. Here we report on the genetic investigation of an atypical XX male in which the SRY gene was located at the end of the long arm of chromosome 1. The patient, with a normal male phenotype, was referred for azoospermia. Conventional cytogenetic analysis showed a 46,XX karyotype. Molecular-cytogenetics (FISH) and molecular (PCR and MLPA) studies identified not only Yp-specific sequences located on the distal long arm of chromosome 1 but also the deletion of the subtelomeric 1qter region. A specific phenotype has been reported for a deletion of the 1qter region associated with mental retardation. The molecular investigation of the 1qter region showed that in our patient the microdeletion is more telomeric than in patients reported with mental retardation. To our knowledge, this is the first report of a XX male with the Yp region transferred to the terminal long arm of chromosome 1. This is also the first microdeletion of the subtelomeric 1qter region not associated with mental retardation.

Up-regulation of SOX9 in human sex-determining region on the Y chromosome (SRY)-negative XX males

BACKGROUND

In mammals, gonadal sex is normally determined by the presence or absence of the Y chromosome gene SRY. After expression of SRY in the sexually indifferent gonad, a number of genes encoding transcription factors and growth factors implicated in testis differentiation start to show male-specific expression. However, in XX males, these genes must be up-regulated in the absence of SRY, but the aetiology of SRY-negative XX maleness remains unclear.

AIM AND METHODS

We examined the expression of representative gonad marker genes in SRY-negative XX male testes.

RESULTS

RT-PCR and immunohistochemical studies revealed that SOX9, DAX-1, Ad4BP/SF-1, WT-1, GATA-4 and MIS were expressed in testicular tissues of SRY-negative XX males. Expression levels of SOX9 in testes of these patients averaged 1.9-fold higher than in normal XY testes, while expression levels of Ad4BP/SF-1, DAX-1 and MIS were lower in the SRY-negative XX testes than in XY testes. All XX patients were found to carry two copies of the SOX9 gene per diploid genome as do normal XX females and XY males. The XX male patients also carried two copies of the DAX-1 gene as do normal XX females, while normal XY males carry a single DAX-1 gene.

CONCLUSIONS

Our data suggest that lesions affecting SOX9 expression are the key factor in sex determination in SRY-negative XX males, and that the decreased expression of Ad4BP/SF-1, DAX-1 and MIS contribute to their clinical features.

Clinical, endocrinological, and epigenetic features of the 46,XX male syndrome, compared with 47,XXY Klinefelter patients

CONTEXT

The 46,XX male syndrome represents a rare, poorly characterized form of male hypogonadism.

OBJECTIVE

The objective of the study was to distinguish the 46,XX male syndrome from the more frequent 47,XXY-Klinefelter syndrome in regard to clinical, hormonal, and epigenetic features.

DESIGN

This was a case-control study.

SETTING

The study was conducted at a university-based reproductive medicine and andrology institution.

PATIENTS

Eleven SRY-positive 46,XX males were compared with age-matched controls: 101 47,XXY Klinefelter patients, 78 healthy men, and 157 healthy women [latter all heterozygous for androgen receptor (AR) alleles].

INTERVENTIONS

There were no interventions.

MAIN OUTCOME MEASURES

There was a comparison of phenotype, endocrine profiles, and X-chromosomal inactivation patterns of AR alleles.

RESULTS

The 46,XX males were significantly smaller than Klinefelter patients or healthy men, resembling female controls in height and weight. The incidence of maldescended testes was significantly higher than that in Klinefelter patients and controls. Gynecomastia was more frequent in comparison with controls, whereas there was a nonsignificant trend in comparison with Klinefelter patients. All XX males were infertile and most were hypogonadal. The inactivation patterns of AR alleles in XX males were significantly more skewed than in Klinefelter patients and women. Seven of 10 heterozygous XX male patients displayed an extreme skewing of more than 80% with no preference toward the shorter or longer AR allele. The length of the AR CAG repeat polymorphism was positively related to traits of hypogonadism.

CONCLUSIONS

XX males are distinctly different from Klinefelter patients in terms of clinical and epigenetic features. Nonrandom X chromosome inactivation ratios are common in XX males, possibly due to the translocated SRY gene. The existence of a Y-chromosomal, growth-related gene is discussed.

An Sry-Positive 46,XX Male

The 46,XX karyotype in a male is a rare sex chromosomal disorder. It mostly results from unequal crossovers between the X and Y chromosomes during meiosis. We here report a 32-year-old infertile male in whom seminal analysis showed azoospermia. Chromosomal analysis revealed a 46,XX karyotype and fluorescentin situhybridization (FISH) showed the presence of the SRY gene. This report highlights the value of karyotyping and FISH analysis in cases of infertility.

SYCE2 is required for synaptonemal complex assembly, double strand break repair, and homologous recombination

Synapsis is the process by which paired chromosome homologues closely associate in meiosis before crossover. In the synaptonemal complex (SC), axial elements of each homologue connect through molecules of SYCP1 to the central element, which contains the proteins SYCE1 and -2. We have derived mice lacking SYCE2 protein, producing males and females in which meiotic chromosomes align and axes form but do not synapse. Sex chromosomes are unaligned, not forming a sex body. Additionally, markers of DNA breakage and repair are retained on the axes, and crossover is impaired, culminating in both males and females failing to produce gametes. We show that SC formation can initiate at sites of SYCE1/SYCP1 localization but that these points of initiation cannot be extended in the absence of SYCE2. SC assembly is thus dependent on SYCP1, SYCE1, and SYCE2. We provide a model to explain this based on protein–protein interactions.

Analysis of sex chromosome abnormalities using X and Y chromosome DNA tiling path arrays

BACKGROUND

Array comparative genomic hybridisation is a powerful tool for the detection of copy number changes in the genome.

METHODS

A human X and Y chromosome tiling path array was developed for the analysis of sex chromosome aberrations.

RESULTS

Normal X and Y chromosome profiles were established by analysis with DNA from normal fertile males and females. Detection of infertile males with known Y deletions confirmed the competence of the array to detect AZFa, AZFb and AZFc deletions and to distinguish between different AZFc lesions. Examples of terminal and interstitial deletions of Xp (previously characterised through cytogenetic and microsatellite analysis) have been assessed using the arrays, thus both confirming and refining the established deletion breakpoints. Breakpoints in iso-Yq, iso-Yp and X-Y translocation chromosomes and X-Y interchanges in XX males are also amenable to analysis.

DISCUSSION

The resolution of the tiling path clone set used allows breakpoints to be placed within 100-200 kb, permitting more precise genotype/phenotype correlations. These data indicate that the combined X and Y tiling path arrays provide an effective tool for the investigation and diagnosis of sex chromosome copy number aberrations and rearrangements.

Klinefelter syndrome and other sex chromosomal aneuploidies

The term Klinefelter syndrome (KS) describes a group of chromosomal disorder in which there is at least one extra X chromosome to a normal male karyotype, 46,XY. XXY aneuploidy is the most common disorder of sex chromosomes in humans, with prevalence of one in 500 males. Other sex chromosomal aneuploidies have also been described, although they are much less frequent, with 48,XXYY and 48,XXXY being present in 1 per 17,000 to 1 per 50,000 male births. The incidence of 49,XXXXY is 1 per 85,000 to 100,000 male births. In addition, 46,XX males also exist and it is caused by translocation of Y material including sex determining region (SRY) to the X chromosome during paternal meiosis. Formal cytogenetic analysis is necessary to make a definite diagnosis, and more obvious differences in physical features tend to be associated with increasing numbers of sex chromosomes. If the diagnosis is not made prenatally, 47,XXY males may present with a variety of subtle clinical signs that are age-related. In infancy, males with 47,XXY may have chromosomal evaluations done for hypospadias, small phallus or cryptorchidism, developmental delay. The school-aged child may present with language delay, learning disabilities, or behavioral problems. The older child or adolescent may be discovered during an endocrine evaluation for delayed or incomplete pubertal development with eunuchoid body habitus, gynecomastia, and small testes. Adults are often evaluated for infertility or breast malignancy. Androgen replacement therapy should begin at puberty, around age 12 years, in increasing dosage sufficient to maintain age appropriate serum concentrations of testosterone, estradiol, follicle stimulating hormone (FSH), and luteinizing hormone (LH). The effects on physical and cognitive development increase with the number of extra Xs, and each extra X is associated with an intelligence quotient (IQ) decrease of approximately 15-16 points, with language most affected, particularly expressive language skills.

An XX male with the sex-determining region Y gene inserted in the long arm of chromosome 16

OBJECTIVE

To report a case of a 46,XX male with an insertion of the sex-determining region Y (SRY) region in the terminal end of the long arm of chromosome 16.

DESIGN

Case report.

SETTING

Molecular and cytogenetic units in a university hospital.

PATIENT(S)

An infertile male, with normal masculinization of the external genitalia, who was referred for chromosomal analysis as an unaffected member of a family with idiopathic hypertrophic osteoarthropathy.

INTERVENTION(S)

Cytogenetic investigation, physical examination, and hormonal assays.

MAIN OUTCOME MEASURE(S)

Chromosomal analysis using GTG banding and fluorescence in situ hybridization (FISH).

RESULT(S)

Conventional chromosome analysis revealed a normal 46,XX karyotype. The FISH with bacterial artificial chromosomes (BACs) of the SRY region indicated the presence of this region on the terminal end of the long arm of chromosome 16.

CONCLUSION(S)

This is the first case of a 46,XX male with the SRY gene present on an autosome-here chromosome 16. The size of the inserted region containing SRY, inserted in 16qter, is approximately 600 kb.

Complex mosaicism in sex reversed SRY+ male twins

Sex reversal is characterized by discordance between genetic and phenotypic sex. Most XX males result from an unequal interchange between X and Y chromosomes during paternal meiosis, therefore transferring SRY to the X chromosome, which explains the male development in the presence of an otherwise normal female karyotype. We present here the case of sex reversed SRY+ male twins with several cell lines. They consulted for infertility. The presence of SRY on an X chromosome was demonstrated by FISH. Their respective karyotypes were: 46,X,der(X)t(X;Y)(p22.3;p11.2)[249]/45,X [12]/45,der(X)t(X;Y)(p22.3;p11.2)[11]/47,XX,der(X)t(X;Y) (p22.3;p11.2)[1]/47,X,der(X)t(X;Y)(p22.3;p11.2)x2[1]/50, XX,der(X)t(X;Y)(p22.3;p11.2)x4[1]/46,XX[1] for the first twin (SH-1) and 46,X,der(X)t(X;Y)(p22.3;p11.2)[108]/45,X [3]/47,XX,der(X)t(X;Y)(p22.3;p11.2)[2]/45,der(X)t(X;Y) (p22.3;p11.2)[1]/47,X,der(X)t(X;Y)(p22.3;p11.2)x2[1] for the second twin (SH-2). There are three different types of XX males: 1) with normal genitalia, 2) with genital ambiguity, and 3) XX true hermaphrodites. The phenotype of the twins presented in this report is consistent with what is generally seen in XX SRY+ males: they have normal genitalia.

Clinical, hormonal and cytogenetic evaluation of 46,XX males and review of the literature

The main factor influencing the sex determination of an embryo is the genetic sex determined by the presence or absence of the Y chromosome. However, some individuals carry a Y chromosome but are phenotypically female (46,XY females) or have a female karyotype but are phenotypically male (46,XX males). 46,XX maleness is a rare sex reversal syndrome affecting 1 in 20,000 newborn males. Molecular analysis of sex-reversed patients led to the discovery of the SRY gene (sex-determining region on Y). The presence of SRY causes the bipotential gonad to develop into a testis. The majority of 46, SRY-positive XX males have normal genitalia; in contrast SRY-negative XX males usually have genital ambiguity. A small number of SRY-positive XX males also present with ambiguous genitalia. Phenotypic variability observed in 46,XX sex reversed patients cannot be explained only by the presence or absence of SRY despite the fact that SRY is considered to be the major regulatory factor for testis determination. There must be some other genes either in the Y or other autosomal chromosomes involved in the definition of phenotype. In this article, we evaluate four patients with 46,XX male syndrome with various phenotypes. Two of these cases are among the first reported to be diagnosed prenatally.

Aspects moléculaires du déterminisme sexuel : régulation génique et pathologie

Testis determination is the complex process by which the bipotential gonad becomes a normal testis during embryo development. As a consequence, this process leads to sexual differentiation corresponding to the masculinization of both genital track and external genitalia. The whole phenomenon is under genetic control and is particularly driven by the presence of the Y chromosome and by the SRY gene, which acts as the key initiator of the early steps of testis determination. However, many other autosomal genes, present in both males and females, are expressed during testis formation in a gene activation pathway, which is far to be totally elucidated. All these genes act in a dosage-sensitive manner by which quantitative gene abnormalities, due to chromosomal deletions, duplications or mosaicism, may lead to testis determination failure and sex reversal.

Skewed X-chromosome inactivation pattern in SRY positive XX maleness: a case report and review of literature

XX maleness is the most common condition in which testes develop in the absence of a cytogenetically detectable Y chromosome. Using fluorescence in situ hybridization (FISH) or PCR, it was possible to detect the transfer of Yp fragments including SRY gene to the terminal part of X chromosome in the majority of XX males. We report a 32-year-old-male in whom a seminal analysis showed azoospermia, an X chromatin analysis showed 44% of Barr body positive nuclei and a chromosomal analysis revealed a 46,XX karyotype. Physical examination showed a normal sexual development and bilateral small testes. Hormonal studies revealed hypergonadotropic hypogonadism. Testis histological examination showed a profile of Sertoli Only Cell Syndrome. FISH study ruled out the presence of a Y-bearing cell line, and confirmed translocation of SRY to Xp terminal part. In order to confirm that the complete masculinized phenotype was related to a preferential inactivation of the no rearranged X chromosome, X-chromosome inactivation patterns (XCIP) were studied by analysis of methylation status of the androgen receptor gene. Highly skewed XCIP was observed by greater than 90% preferential inactivation involving one of the two X chromosomes, suggesting that the SRY-bearing X chromosome was the preferentially active X allowing for sufficient SRY expression for complete masculinization.

Early manifestations of testicular dysgenesis in children: pathological phenotypes, karyotype correlations and precursor stages of tumour development

Testicular dysgenesis derives from abnormal gonadal development caused by chromosome aberrations/mosaicisms or mutations/deletions in SRY or other genes responsible for testicular differentiation. Dysgenetic male pseudohaermaphroditism has bilateral dysgenetic testes characterized by a cortical network of anastomosing seminiferous cords that penetrate a thin albuginea. In asymmetric gonadal differentiation (or Mixed Gonadal Dysgenesis) a dysgenetic testis associates with a streak gonad with primitive sex cords embedded in an ovarian-like stroma. Uni- or bilateral ovotestes identify true haermaphroditism. Fluorescent in situ hybridisation studies demonstrate that the sex chromosomes of mosaic patients do not distribute homogeneously in asymmetric gonads. 45,X lines predominate over 46,XY in streak gonads, while the relationship between these two is more equivalent in dysgenetic testes, suggesting that testicular or streak differentiation is related to the balance between X0 and XY lines. Testicular dys-genesis is more severe when there is a frank predominance of X0 or XX cells. Higher percentages of XY cells coincide with lesser degrees of dysgenesis. DNA densitometry indicate a higher incidence of neoplastic transformation than previously anticipated. Various specimens showed clear aneuploid histograms but no clear indication of a cytological CIS phenotype. There was a wide cytological variation in aneuploid germ cells, ranging from normally looking big infantile spermatogonia to gonocyte/CIS cells. Aneuploidy probably precedes the full expression of the CIS phenotype. In case of doubt we recommend DNA densitometry to either confirm or discard their neoplastic nature. The earliest recognizable change in germ cell tumorigenesis is probably the polyploidisation of fetal germ cells, followed by the expression of the CIS phenotype in isolated germ cells scattered along infantile seminiferous tubules that later proliferate to give an adult type CIS pattern.

Prenatal diagnosis of a 45,X male with a SRY-bearing chromosome 21

Male phenotype associated with a 45,X karyotype is an infrequent finding. We present a case diagnosed prenatally on amniocentesis performed for maternal age. The male phenotype was associated with a translocation of a distal part of Yp including the pseudoautosomal SHOX gene and SRY gene on the short arm of a chromosome 21. By DNA analysis we could show that the X chromosome was of maternal origin and that the breakpoint was in interval 3 of the Y chromosome. Mechanisms and genetic counselling are discussed based on a review of published cases of 45,X and XX males.

Identifying genes for male sex determination in humans

The convergence of genetic and molecular technologies has led to the identification of a number of genes for male sex determination. The observation of chromosomal translocations, deletions, and duplications in sex reversed individuals was instrumental for the positional cloning of SRY, SOX9, WT1, and DAX1. Cloning by protein-DNA interaction was required for the identification of SF1. The observation of an extended phenotype for the alpha thalassemia-mental retardation syndrome assigned a role for XH2 in the testicular determining process. Over the next several years, new sex determining genes will be identified by linkage analysis in large families with multiple sex reversed members, comparative genomic hybridization of sex reversed individuals, and database searches for genes that encode interacting proteins or paralogs of other species. Given the apparent differences in the sex determining mechanisms of even closely related species, the roles of all of these genes will require confirmation by demonstrating expression in human gonadal ridge at the critical time, and that mutations result in sex reversal.

Sry, Sox9 and mammalian sex determination

Sry is the Y-chromosomal gene that acts as a trigger for male development in mammalian embryos. This gene encodes a high mobility group (HMG) box transcription factor that is known to bind to specific target sequences in DNA and to cause a bend in the chromatin. DNA bending appears to be part of the mechanism by which Sry influences transcription of genes downstream in a cascade of gene regulation leading to maleness, but the factors that cooperate with, and the direct targets of, Sry remain to be identified. One gene known to be downstream from Sry in this cascade in Sox9, which encodes a transcription factor related to Sry by the HMG box. Like Sry, mutations in Sox9 disrupt male development, but unlike Sry, the role of Sox9 is not limited to mammals. This review focuses on what is known about the two genes and their likely modes of action, and draws together recent data relating to how they might interconnect with the network of gene activity implicated in testis determination in mammals.

Steroid sulphatase levels in XX males, including observations on two affected cousins

Quantitative assays of steroid sulphatase in XX males have shown that some individuals have two functional loci, and others only one. Two affected cousins, who cannot share the same X-chromosome, nevertheless have male levels of steroid sulphatase, suggesting functional abnormality of the X chromosome. The hypothesis is advanced that these and other unusual features of X-chromosome function in some XX males, could be explained if such cases were due to an autosomal mutation, exercising its effect by causing abnormal inactivation of a subterminal area of Xp which normally escapes the inactivation process.

Localization of the sex-determining region-Y gene in XX males

Localization of the sex-determining region Y (SRY) was investigated in 2 XX males. Metaphase chromosomes from peripheral lymphocytes were stained by fluorescence in situ hybridization using DXZ1 and SRY probes. An identical hybridization signal with the SRY probe was found on an X chromosome in both cases. The karyotype of the 2 cases was 46,XX, t(X;Y)(p22.3;p11.3). It would appear that XX male is the presence of a Y-chromosome fragment transferred to the X-chromosome short arm by unequal interchange between homologous regions in the short arms of sex chromosomes.