Nonrandom inactivation of the Y-bearing X chromosome in a 46,XX individual: evidence for the etiology of 46,XX true hermaphroditism

Comprehensive analysis of three female patients with different types of X/Y translocations and literature review

BACKGROUND

X/Y translocations are highly heterogeneity in terms of clinical genetic effects, and most patients lack complete pedigree analysis for clinical and genetic characterization.

RESULTS

This study comprehensively analyzed the clinical and genetic characteristics of three new patients with X/Y translocations. Furthermore, cases with X/Y translocations reported in the literature and studies exploring the clinical genetic effects in patients with X/Y translocations were reviewed. All three female patients were carriers of X/Y translocations with different phenotypes. The karyotype for patient 1 was 46,X,der(X)t(X;Y)(p22.33;q12)mat, patient 2 was 46,X,der(X)t(X;Y)(q21.2;q11.2)dn, and patient 3 was 46,X,der(X)t(X;Y)(q28;q11.223)t(Y;Y)(q12;q11.223)mat. C-banding analysis of all three patients revealed a large heterochromatin region in the terminal region of the X chromosome. All patients underwent chromosomal microarray analysis, which revealed the precise copy number loss or gain. Data on 128 patients with X/Y translocations were retrieved from 81 studies; the phenotype of these patients was related to the breakpoint of the chromosome, size of the deleted region, and their sex. We reclassified the X/Y translocations into new types based on the breakpoints of the X and Y chromosomes.

CONCLUSION

X/Y translocations have substantial phenotypic diversity, and the genetic classification standards are not unified. With the development of molecular cytogenetics, it is necessary to combine multiple genetic methods to obtain an accurate and reasonable classification. Thus, clarifying their genetic causes and effects promptly will help in genetic counseling, prenatal diagnosis, preimplantation genetic testing, and improvement in clinical treatment strategies.

Identification of an SRY-negative 46,XX infertility male with a heterozygous deletion downstream of SOX3 gene

Background

A male individual with a karyotype of 46,XX is very rare. We explored the genetic aetiology of an infertility male with a kayrotype of 46,XX and SRY negative.

Methods

The peripheral blood sample was collected from the patient and subjected to a few genetic testing, including chromosomal karyotyping, azoospermia factor (AZF) deletion, short tandem repeat (STR) analysis for AMELX, AMELY and SRY, fluorescence in situ hybridization (FISH) with specific probes for CSP 18/CSP X/CSP Y/SRY, chromosomal microarray analysis (CMA) for genomic copy number variations(CNVs), whole-genome analysis(WGA) for genomic SNV&InDel mutation, and X chromosome inactivation (XCI) analysis.

Results

The patient had a karyotype of 46,XX. AZF analysis showed that he missed the AZF region (including a, b and c) and SRY gene. STR assay revealed he possessed the AMELX in the X chromosome, but he had no the AMELY and SRY in the Y chromosome. FISH analysis with CSP X/CSP Y/SRY showed only two X centromeric signals, but none Y chromosome and SRY. The above results of the karyotype, FISH and STR analysis did not suggest a Y chromosome chimerism existed in the patient's peripheral blood. The result of the CMA indicated a heterozygous deletion with an approximate size of 867 kb in Xq27.1 (hg19: chrX: 138,612,879–139,480,163 bp), located at 104 kb downstream of SOX3 gene, including F9, CXorf66, MCF2 and ATP11C. WGA also displayed the above deletion fragment but did not present known pathogenic or likely pathogenic SNV&InDel mutation responsible for sex determination and development. XCI assay showed that he had about 75% of the X chromosome inactivated.

Conclusions

Although the pathogenicity of 46,XX male patients with SRY negative remains unclear, SOX3 expression of the acquired function may be associated with partial testis differentiation of these patients. Therefore, the CNVs analysis of the SOX3 gene and its regulatory region should be performed routinely for these patients.

Clinical and molecular studies in four patients with SRY-positive 46,XX testicular disorders of sex development: implications for variable sex development and genomic rearrangements

We report four patients with SRY-positive 46,XX testicular disorders of sex development (46,XX-TDSD) (cases 1-4). Case 1 exhibited underdeveloped external genitalia with hypospadias, case 2 manifested micropenis and cases 3 and 4 showed normal external genitalia. The Xp;Yp translocations occurred between the X- and the Y-differential regions in case 1, between PRKX and inverted PRKY in case 2 and between the X-chromosomal short arm pseudoautosomal region and the Y-differential regions in cases 3 and 4. The distance of the Yp breakpoint from SRY was ~0.75 Mb in case 1, ~6.5 Mb in case 2, ~2.3 Mb in case 3 and ~72 kb in case 4. The Xp;Yp translocation occurred within an 87-bp homologous segment of PRKX and PRKY in case 2, and between non-homologous regions with addition of an 18-bp sequence of unknown origin in case 4. X-inactivation analysis revealed random inactivation in cases 1-4. The results argue against the notion that undermasculinization in 46,XX-TDSD is prone to occur when translocated Yp materials are small (<100 kb of the Y-differential region), and imply that the Xp;Yp translocations result from several mechanisms including non-allelic homologous recombination and non-homologous end joining.

A practical approach to ambiguous genitalia in the newborn period

The evaluation and management of neonates with ambiguous genitalia requires sensitivity, efficiency, and accuracy. The approach to these neonates is facilitated by a multidisciplinary team including urology, endocrinology, genetics, and psychiatry or psychology. Disorders of sex development (DSD) encompass chromosomal DSD, 46,XX DSD, and 46,XY DSD. The 46,XX DSD is the most common DSD and in the majority of these children congenital adrenal hyperplasia is the underlying etiology. The 46,XY DSD is a heterogeneous disorder that often results from a disruption in the production or response to testosterone, dihydrotestosterone, or Mullerian inhibitory substance. Chromosomal DSD includes conditions resulting from abnormal meiosis, including Klinefelter syndrome (47, XXY) and Turner syndrome. The evaluation of children with DSD demands a thorough physical examination, medical history, karyotype, metabolic panel, 17-OH progesterone, testosterone, luteinizing hormone, follicle stimulation hormone, and urinalysis. A radiographic evaluation should begin with an abdominal and pelvic ultrasound but may include magnetic resonance imaging, endoscopy, or laparoscopy.

Control of sex development

The process of sexual differentiation is central for reproduction of almost all metazoan, and therefore, for maintenance of practically all multicellular organisms. In sex development, we can distinguish two different processes, sex determination, that is the developmental decision that directs the undifferentiated embryo into a sexually dimorphic individual. In mammals, sex determination equals gonadal development. The second process known as sex differentiation takes place once the sex determination decision has been made through factors produced by the gonads that determine the development of the phenotypic sex. Most of the knowledge on the factors involved in sexual development came from animal models and from studies of cases in whom the genetic or the gonadal sex does not match the phenotypical sex, that is, patients affected by disorders of sex development (DSDs). Generally speaking, factors influencing sex determination are transcriptional regulators, whereas factors important for sex differentiation are secreted hormones and their receptors. This review focuses on these factors and whenever possible, references regarding the 'prismatic' clinical cases are given.

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.

Phenotype in X chromosome rearrangements: pitfalls of X inactivation study

OBJECTIVE

X inactivation pattern in X chromosome rearrangements usually favor the less unbalanced cells. It is correlated to a normal phenotype, small size or infertility. We studied the correlation between phenotype and X inactivation ratio in patients with X structural anomalies.

PATIENTS AND METHODS

During the 1999-2005 period, 12 X chromosome rearrangements, including three prenatal cases, were diagnosed in the Laboratoire de Cytogénétique of Strasbourg. In seven cases, X inactivation ratio could be assessed by late replication or methylation assay.

RESULTS

In three of seven cases (del Xp, dup Xp, t(X;A)), X inactivation ratio and phenotype were consistent. The four other cases showed discrepancies between phenotype and X inactivation pattern: mental retardation and dysmorphism in a case of balanced X-autosome translocation, schizophrenia and autism in two cases of XX maleness and MLS syndrome (microphthalmia with linear skin defects) in a case of Xp(21.3-pter) deletion.

CONCLUSION

Discrepancies between X inactivation ratio and phenotype are not rare and can be due to gene disruption, position effect, complex microrearrangements, variable pattern of X inactivation in different tissues or fortuitous association. In this context, the prognostic value of X inactivation study in prenatal diagnosis will be discussed.

A practical approach to intersex in the newborn period

Sexual determination is a complex process that occurs in an organized sequential manner. When chromosomal, gonadal, or phenotypic sex determination goes awry,intersexuality develops. Advances in molecular biology have made it easier to understand the various phenotypes that are encountered. It is easy to be overwhelmed when reviewing the testosterone synthesis pathway and the intersex differential diagnosis. This article presents a useful approach to the evaluation of the newborn with ambiguous genitalia.

Cell proliferation is necessary for the determination of male fate in the gonad

Cell proliferation has been shown to have multiple functions in development and pattern formation, including roles in growth, morphogenesis, and gene expression. Previously, we determined that the earliest known morphological event downstream of the male sex determining gene, Sry, is the induction of proliferation. In this study, we used proliferation inhibitors to block cell division during early gonad development, at stages before the XY gonad has committed to the testis pathway. Using the expression of sex-specific genes and the formation of testis morphology as markers of testis determination, we found that proliferation within a specific 8-h window was critical for the establishment of the male pathway and the formation of the testis. Inhibition of proliferation before or after this critical period led to smaller gonads, but did not block testis formation. The critical period of proliferation coincides with the initiation of Sry expression and is essential for the differentiation of Sertoli cells, suggesting that proliferation is a vital component of the initiation of the male pathway by Sry. We believe these studies suggest that proliferation is involved not only in the elaboration of organ pattern, but also in the choice between patterns (male and female) in the bipotential gonad.

Colocalization of WT1 and cell proliferation reveals conserved mechanisms in temperature-dependent sex determination

During vertebrate development the gonad has two possible fates, the testis or the ovary. The choice between these fates is made by a variety of sex-determining mechanisms, from the sex-determining gene on the Y chromosome (Sry) in mammals, to nongenetic temperature-dependent systems in many reptiles. Despite the differences in the mechanisms at the top of the sex-determining cascade, the resulting morphology and many genes involved in early testis and ovarian development are common to most vertebrates, leading to the hypothesis that the underlying processes of sex determination are conserved. In this study, we examined the early steps of gonad development in the red-eared slider turtle (Trachemys scripta), a species that uses the temperature of egg incubation to determine sex. A dramatic increase in cell proliferation was observed in the male gonad during the earliest stages of sex determination. Using the localization of Wilms' Tumor suppressor 1 (WT1), we determined that this proliferation increase occurred in a population that contained pre-Sertoli cells. The proliferation of pre-Sertoli cells has been documented during sex determination in both mice and alligators, suggesting that proliferation of this cell type has an important role in vertebrate testis organogenesis and the determination of male fate.

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.

Expression of the human SRY protein during development in normal male gonadal and sex-reversed tissues

Sex determination in mammals is controlled by the SRY gene located on the Y chromosome. It encodes a protein containing a DNA-binding and DNA-bending domain. In spite of recent advances in the identification of the mechanisms that regulate male sex determination in mammals, the expression profile of the SRY protein in normal and sex-reversed human tissues is not well established. In order to localize the SRY protein and determine its cellular distribution and expression at different stages of development, we prepared monoclonal antibodies (mAb) against the recombinant SRY protein. One of these antibodies, LSRY1.1, recognizes a protein of 27 kDa in total lysates of HeLa SRYB3, a human cell line transfected with the SRY gene under the control of the SV40 promoter. Immunocytochemical analysis in the cell lines shows nuclear localization of the SRY protein. We have studied SRY protein expression in human tissues at different stage of fetal development until adult life and have demonstrated that the SRY protein is located in the nuclei of somatic cells and germ cells in the genital ridge during testis development. After testis determination, it can be detected until the adult stage in both germ cells and Sertoli cells. The presence of the SRY protein was also analyzed in biopsies of gonadal tissues of sex-reversal patients such as SRY-positive 46,XX males or SRY-positive 46,XX true hermaphrodites. SRY protein is detected in the nuclei of Sertoli cells of the testis and in the nuclei of granulosa cells in the ovotestis in these patients and in the nuclei of germ cells of both tissue types. These results suggest a common cellular origin for both Sertoli cells and granulosa cells.

Testis determination in mammals: more questions than answers

In humans, testis development depends on a regulated genetic hierarchy initiated by the Y-linked SRY gene. Failure of testicular determination results in the condition termed 46,XY gonadal dysgenesis (GD). Several components of the testis determining pathway have recently been identified though it has been difficult to articulate a cascade with the known elements of the system. It seems, however, that early gonadal development is the result of a network of interactions instead of the outcome of a linear cascade. Accumulating evidence shows that testis formation in man is sensitive to gene dosage. Haploinsufficiency of SF1, WT1 and SOX9 is responsible for 46,XY gonadal dysgenesis. Besides, data on SRY is consistent with possible dosage anomalies in certain cases of male to female sex reversal. 46,XY GD due to monosomy of distal 9p and 10q might also be associated with an insufficient gene dosage effect. Duplications of the locus DSS can lead to a failure of testicular development and a duplication of the region containing SOX9 has been implicated in XX sex reversal. Transgenic studies in mouse have shown, however, that this mammal is less sensitive to gene dosage than man. Here, we will try to put in place the known pieces of the jigsaw puzzle that is sex determination in mammals, as far as current knowledge obtained from man and animal models allows. We are certain that from this attempt more questions than answers will arise.

SRY gene transferred to the long arm of the X chromosome in a Y-positive XX true hermaphrodite

Yp-specific sequences, including the testicular determinant gene SRY, have been detected and located in a 46,XX true hermaphrodite individual, using PCR amplification and fluorescent in situ hybridization (FISH). Among different Y chromosome loci tested, it was only possible to detect Yp sequences. The Y-centromere and Yq sequences were absent. Unexpectedly, the Y fragment was translocated to the long arm of one of the X chromosomes, at the Xq28 level, and the derivative (X) chromosome of the patient lacked q-telomeric sequences. To our knowledge, this is the first Yp/Xq translocation reported. The coexistence of testicular and ovarian tissue in the patient may have arisen by differential inactivation of the Y-bearing X chromosome, in which Xq telomeric sequences are missing. The possible origin of the Yp/Xq translocation, during paternal meiosis or in somatic paternal cells, is discussed.

Incomplete masculinisation of XX subjects carrying the SRY gene on an inactive X chromosome

46,XX subjects carrying the testis determining SRY gene usually have a completely male phenotype. In this study, five very rare cases of SRY carrying subjects (two XX males and three XX true hermaphrodites) with various degrees of incomplete masculinisation were analysed in order to elucidate the cause of sexual ambiguity despite the presence of the SRY gene. PCR amplification of 20 Y chromosome specific sequences showed the Yp fragment to be much longer in XX males than in true hermaphrodites. FISH analysis combined with RBG banding of metaphase chromosomes of four patients showed that in all three true hermaphrodites and in one XX male the Yp fragment was translocated onto a late replicating inactive X chromosome in over 90% of their blood lymphocytes. However, in a control classical XX male with no ambiguous features, the Yp fragment (significantly shorter than in the XX male with sexual ambiguity and only slightly longer than in XX hermaphrodites) was translocated onto the active X chromosome in over 90% of cells.

These studies strongly indicate that inactivation on the X chromosome spreading into a translocated Yp fragment could be the major mechanism causing a sexually ambiguous phenotype in XX (SRY+) subjects.

Abnormalities of gonadal differentiation

Gonadal differentiation involves a complex interplay of developmental pathways. The sex determining region Y (SRY) gene plays a key role in testis determination, but its interaction with other genes is less well understood. Abnormalities of gonadal differentiation result in a range of clinical problems. 46,XY complete gonadal dysgenesis is defined by an absence of testis determination. Subjects have female external genitalia and come to clinical attention because of delayed puberty. Individuals with 46,XY partial gonadal dysgenesis usually present in the newborn period for the valuation of ambiguous genitalia. Gonadal histology always shows an abnormality of seminiferous tubule formation. A diagnosis of 46,XY true hermaphroditism is made if the gonads contain well-formed testicular and ovarian elements. Despite the pivotal role of the SRY gene in testis development, mutations of SRY are unusual in subjects with a 46,XY karyotype and abnormal gonadal development. 46,XX maleness is defined by testis determination in an individual with a 46,XX karyotype. Most affected individuals have a phenotype similar to that of Klinefelter syndrome. In contrast, subjects with 46,XX true hermaphroditism usually present with ambiguous genitalia. The majority of subjects with 46,XX maleness have Y sequences including SRY in genomic DNA. However, only rare subjects with 46,XX true hermaphroditism have translocated sequences encoding SRY. Mosaicism and chimaerism involving the Y chromosome can also be associated with abnormal gonadal development. However, the vast majority of subjects with 45,X/46,XY mosaicism have normal testes and normal male external genitalia.

Ovotestes in B6-XXSxr sex-reversed mice

The sex-reversed mutation Sxr results in XX males. In the absence of any other mutations, testis differentiation in XXSxr fetuses is essentially normal and only one report of an XXSxr fetus with ovotestes is in the literature. We report that 84% (21/25) of 13 days postcoitum XXSxr fetuses on the B6 inbred genomic background have ovotestes. Ovotestes were found in fetuses from both Sxra and Sxrb variants. Examination of fetuses older than 13 dpc suggests that the presence of ovotestes is transient in most fetuses. However, one overt hermaphrodite was identified after birth. The development of ovotestes is associated with the inbred background and is exacerbated by the dominant spotting oncogene allele KitW-42J. We propose that spreading of X-inactivation into the Sxr region resulting in loss of Sry expression is more extensive in B6-Sxr strains.

Development in a 46 XX boy with positive SRY gene

We present the case of an 11 year-old boy, who asked for medical attention due to obesity and assumed underdeveloped external genitalia. He did not have genital anomalies, penile length was 5.3 cm, testicular volume 2 ml and pubic hair Tanner stage 1. His bone age was normal for chronological age. Endocrinological study showed normal results for his age. Karyotype revealed a 46 XX pattern. MRI of external genitalia showed bilateral scrotal testes which were normal in diameter for his age. The check of his historical growth chart and follow-up revealed normal growth with spontaneous pubertal development. However, hormonal studies showed progressive increase of FSH levels, indicative of failure of germinal epithelium. The presence of Y sequences, including SRY gene, was demonstrated by PCR. Our observation is in agreement with the view that 46 XX male subjects diagnosed at peripubertal age with the SRY gene in the genome have a good prognosis regarding growth and development, but the principal problem of these patients is infertility.

The role of SRY in mammalian sex determination

The gene SRY (sex determining region of the Y), located at the distal region of the short arm of the Y chromosome, is necessary for male sex determination in mammals. SRY initiates the cascade of steps necessary to form a testis from an undifferentiated gonad. The SRY gene encodes an HMG (High Mobility Group) protein which may act as a transcription factor by binding to double stranded DNA and then bending the DNA. Mutations in SRY have been identified in some subjects with 46,XY pure gonadal dysgenesis. However the role for other autosomal and X-linked genes in testis determination is evident by the presence of a normal SRY gene in the majority of females with 46,XY pure gonadal dysgenesis and the lack of SRY in a minority of males with 46,XY maleness.

Molecular analysis in true hermaphrodites with different karyotypes and similar phenotypes

True hermaphroditism is characterized by the development of ovarian and testicular tissue in the same individual. Müllerian and Wolffian structures are usually present, and external genitalia are often ambiguous. The most frequent karyotype in these patients is 46,XX or various forms of mosaicism, whereas 46,XX is very rarely found. The phenotype in all these subjects is similar. We studied 10 true hermaphrodites. Six of them had a 46,XX chromosomal complement: 3 had been reared as males and 3 as females. The other 4 patients were mosaics: 3 were 46,XX/46,XY and one had a 46,XX/47,XXY karyotype. One of the 46,XX/46,XY mosaics was reared as a female, whereas the other 3 mosaics were reared as males. The sex of assignment in the 10 patients depended only on labio-scrotal differentiation. Molecular studies in 46,XX subjects documented the absence of Y centromeric sequences in all cases, arguing against hidden mosaicism. One patient presented Yp sequences (ZFY+, SRY+), which contrast with South African black 46,XX true hermaphrodites in whom no Y sequences were found. Molecular analysis in the subjects with mosaicism demonstrated the presence of Y centromeric and Yp sequences confirming the presence of a Y chromosome. Gonadal development, endocrine function, and phenotype in the 10 patients did not correlate with the presence of a Y chromosome or Y-derived sequences in the genome, confirming that true hermaphroditism is a heterogeneous condition.