Origin of chi46,XX/46,XY chimerism in a human true hermaphrodite

A case report of a normal fertile woman with 46,XX/46,XY somatic chimerism reveals a critical role for germ cells in sex determination

Individuals with 46,XX/XY chimerism can display a wide range of characteristics, varying from hermaphroditism to complete male or female, and can display sex chromosome chimerism in multiple tissues, including the gonads. The gonadal tissues of females contain both granulosa and germ cells. However, the specific sex chromosome composition of the granulosa and germ cells in 46,XX/XY chimeric female is currently unknown. Here, we reported a 30-year-old woman with secondary infertility who displayed a 46,XX/46,XY chimerism in the peripheral blood. FISH testing revealed varying degrees of XX/XY chimerism in multiple tissues of the female patient. Subsequently, the patient underwent preimplantation genetic testing (PGT) treatment, and 26 oocytes were retrieved. From the twenty-four biopsied mature oocytes, a total of 23 first polar bodies (PBs) and 10 second PBs were obtained. These PBs and two immature metaphase I (MI) oocytes only displayed X chromosome signals with no presence of the Y, suggesting that all oocytes in this chimeric female were of XX germ cell origin. On the other hand, granulosa cells obtained from individual follicles exhibited varied proportions of XX/XY cell types, and six follicles possessed 100% XX or XY granulosa cells. A total of 24 oocytes were successfully fertilized, and 12 developed into blastocysts, where 5 being XY and 5 were XX. Two blastocysts were transferred with one originating from an oocyte aspirated from a follicle containing 100% XY granulosa cells. This resulted in a twin pregnancy. Subsequent prenatal diagnosis confirmed normal male and female karyotypes. Ultimately, healthy boy-girl twins were delivered at full term. In summary, this 46,XX/XY chimerism with XX germ cells presented complete female, suggesting that germ cells may exert a significant influence on the sexual determination of an individual, which provide valuable insights into the intricate processes associated with sexual development and reproduction.

Obligate chimerism in male yellow crazy ants

Multicellular organisms typically develop from a single fertilized egg and therefore consist of clonal cells. We report an extraordinary reproductive system in the yellow crazy ant. Males are chimeras of haploid cells from two divergent lineages: R and W. R cells are overrepresented in the males' somatic tissues, whereas W cells are overrepresented in their sperm. Chimerism occurs when parental nuclei bypass syngamy and divide separately within the same egg. When syngamy takes place, the diploid offspring either develops into a queen when the oocyte is fertilized by an R sperm or into a worker when fertilized by a W sperm. This study reveals a mode of reproduction that may be associated with a conflict between lineages to preferentially enter the germ line.

Natural human chimeras: A review

The term chimera has been borrowed from Greek mythology and has a long history of use in biology and genetics. A chimera is an organism whose cells are derived from two or more zygotes. Recipients of tissue and organ transplants are artificial chimeras. This review concerns natural human chimeras. The first human chimera was reported in 1953. Natural chimeras can arise in various ways. Fetal and maternal cells can cross the placental barrier so that both mother and child may become microchimeras. Two zygotes can fuse together during an early embryonic stage to form a fusion chimera. Most chimeras remain undetected, especially if both zygotes are of the same genetic sex. Many are discovered accidently, for example, during a routine blood group test. Even sex-discordant chimeras can have a normal male or female phenotype. Only 28 of the 50 individuals with a 46,XX/46,XY karyotype were either true hermaphrodites or had ambiguous genitalia. Blood chimeras are formed by blood transfusion between dizygotic twins via the shared placenta and are more common than was once assumed. In marmoset monkey twins the exchange via the placenta is not limited to blood but can involve other tissues, including germ cells. To date there are no examples in humans of twin chimeras involving germ cells. If human chimeras are more common than hitherto thought there could be many medical, social, forensic, and legal implications. More multidisciplinary research is required for a better understanding of this fascinating subject.

Polar body cytokinesis

Polar body cytokinesis is the physical separation of a small polar body from a larger oocyte or ovum. This maternal meiotic division shares many similarities with mitotic and spermatogenic cytokinesis, but there are several distinctions, which will be discussed in this review. We synthesize results from many different model species, including those popular for their genetics and several that are more obscure in modern cell biology. The site of polar body division is determined before anaphase, by the eccentric, cortically associated meiotic spindle. Depending on the species, either the actin or microtubule cytoskeleton is required for spindle anchoring. Chromatin is necessary and sufficient to elicit differentiation of the associated cortex, via Ran-based signaling. The midzone of the anaphase spindle serves as a hub for regulatory complexes that elicit Rho activation, and ultimately actomyosin contractile ring assembly and contraction. Polar body cytokinesis uniquely requires another Rho family GTPase, Cdc42, for dynamic reorganization of the polar cortex. This is perhaps due to the considerable asymmetry of this division, wherein the polar body and the oocyte/ovum have distinct fates and very different sizes. Thus, maternal meiotic cytokinesis appears to occur via simultaneous polar relaxation and equatorial contraction, since the polar body is extruded from the spherical oocyte through the nascent contractile ring. As such, polar body cytokinesis is an interesting and important variation on the theme of cell division.

Chimerism in black southern African patients with true hermaphroditism 46,XX/47XY,+21 and 46,XX/46,XY

True hermaphroditism is defined by the presence of both testicular and ovarian tissue in an individual. True hermaphrodites usually present at birth with ambiguous genitalia, and subsequent invasive investigations are needed to confirm the diagnosis. Several large cohorts of black South Africans with true hermaphroditism have been described, and by far the majority of those investigated had a 46,XX karyotype, with absence of the SRY sequence. This paper represents the first report of the molecular investigation of mosiacism/chimerism as the cause of hermaphroditism in black southern African patients. It is the second report worldwide of a 46,XX/47,XY,+21 chimera, with the first described in a Japanese infant in 1994. Case 1 in the present study is a child who is a 46,XX/47,XY,+21 tetragametic chimera. Molecular studies revealed two paternal and two maternal alleles at four of ten STR loci investigated and three alleles at four of these loci. The young boy exhibited no features of Down syndrome, other than a unilateral single palmar crease. Cases 2 and 3 both have a 46,XX/46,XY karyotype. Chimerism is supported by molecular analysis in Case 2, and molecular studies were not done for Case 3.

A healthy, female chimera with 46,XX/46,XY karyotype

We report a healthy and unambiguously female newborn, whose phenotypic sex contradicted the expected male sex based on previously performed prenatal cytogenetic analysis. Both 46,XX and 46,XY cells were detected in a villus sample, the former having been attributed to maternal cell contamination. Postnatal karyotyping in peripheral lymphocytes confirmed the presence of two cell lines, one 46,XX (70%) and one 46,XY (30%). After exclusion of alternative explanations for the observed genotype, a diagnosis of chimerism was made. Chimeras containing cell lines of opposite sex usually feature ovotesticular development with associated genital ambiguity. To account for the normal female appearance of our patient, we postulate the exclusive involvement of 46,XX cells in gonad formation.

When "personhood" begins in the embryo: avoiding a syllabus of errors

The following essay was delivered at the conference "Ontogeny and Human Life" at the Ponifical Athenaeum "Regina Apostolorum," November, 2007. Sponsored by the Legion of Christ, the Pontifical Academy for Life, and the John Templeton Foundation, the sessions focused on when the conceptus became a "person." My essay focused on the scientific conclusions that could aid such discussions. Moreover, after listening to the philosophical, legal, and theological discussions that ensued, I responded theologically as well. New concepts in modern embryology have made scientists revise their views concerning the autonomy of embryos and the mechanisms that generate such embryos. There are interactions between the sperm and the female reproductive tract and egg which had never been known until recently. There are also interactions between the developing organism and its environment that had been unsuspected a decade ago. Gut bacteria induce the development of the mammalian digestive system and immune system by changing the gene expression patterns in the mammalian intestine. Conversely, chemicals in our technological society can adversely affect the embryo, rendering it sterile or prone to tumors later in life. While there is no consensus among scientists as to when human life begins, both Church and science can become allies in persuading governments to regulate or ban the production and use of these fetotoxic chemicals. These new views of embryonic development change many of the stories told about human embryos and fetuses, and they have implications concerning the use of science as evidence for theological positions.

A case of true hermaphroditism reveals an unusual mechanism of twinning

Traditionally twins are classified as dizygous or fraternal and monozygous or identical (Hall Twinning, 362, 2003 and 735-743). We report a rare case of 46,XX/46,XY twins: Twin A presented with ambiguous genitalia and Twin B was a phenotypically normal male. These twins demonstrate a third, previously unreported mechanism for twinning. The twins underwent initial investigation with 17-hydroxyprogesterone and testosterone levels, pelvic ultrasound and diagnostic laparoscopy. Cytogenetic analysis was performed on peripheral blood cells and skin fibroblasts. Histological examination and Fluorescence in situ hybridization studies on touch imprints were performed on gonadal biopsies. DNA analysis using more than 6,000 DNA markers was performed on skin fibroblast samples from the twins and on peripheral blood samples from both parents. Twin A was determined to be a true hermaphrodite and Twin B an apparently normal male. Both twins had a 46,XX/46,XY chromosome complement in peripheral lymphocytes, skin fibroblasts, and gonadal biopsies. The proportion of XX to XY cells varied between the twins and the tissues evaluated. Most significantly the twins shared 100% of maternal alleles and approximately 50% of paternal alleles in DNA analysis of skin fibroblasts. The twins are chimeric and share a single genetic contribution from their mother but have two genetic contributions from their father thus supporting the existence of a third, previously unreported type of twinning.

Prenatal Diagnosis and Genetic Analysis of a Fetus with 47,XX, +21/46,XX Mosaicism and XX/XY Chimerism

Prenatal diagnosis of simultaneous occurrence of chimerism and autosomal mosaicism is extremely rare. We report the prenatal diagnosis and genetic analysis of a fetus in a twin pregnancy with mosaic 47,XX,+21/46,XX with chimeric XX/XY. A 36-year-old, para 1, woman was referred for genetic counseling at 20 weeks' gestation because of abnormal karyotype (47,XX,+21/46,XX) in one fetus in a twin pregnancy. Cordocentesis revealed 47,XX,+21[3]/46,XX[35]/46,XY[7] in this fetus. Postnatal cytogenetic analysis of cord blood confirmed three cell lines in this twin (A) and 46,XY in the co-twin (B). Postmortem pathologic findings of both fetuses were normal. Fluorescence in situ hybridization identified three cell lines in the cord blood of twin A. Molecular genetic analysis using polymorphic DNA markers revealed parental origin of fetal tissue, and confirmed the chimeric status. Molecular genetic analysis with polymorphic DNA markers help to differentiate chimerism from mosaicism and define the origin of cell lines, which may have importance in genetic counseling.

Molecular genetic etiology of twin reversed arterial perfusion sequence

OBJECTIVE

Our purpose was to determine whether the twin reversed arterial perfusion sequence (acardiac anomaly) results from fertilization of the first or second polar body.

STUDY DESIGN

Placental or fetal tissue was obtained from nine twin sets discordant for twin reversed arterial perfusion. After deoxyribonucleic acid extraction, the polymerase chain reaction was used to amplify five polymorphic microsatellite repeats. The products were differentiated by polyacrylamide gel electrophoresis, and patterns were compared within twin sets.

RESULTS

Deoxyribonucleic acid fingerprinting patterns were identical in all twin sets for all primer pairs. It is calculated that the chance that any of the acardiac twins resulted from fertilization of either the first or second polar body is <4% and the chance that they all resulted from polar body fertilization is <0.001%.

CONCLUSION

Twins discordant for the twin reversed arterial perfusion sequence anomaly are monozygous. Our results exclude polar body fertilization as a likely cause of this condition.

Chimaerism shown by cytogenetics and DNA polymorphism analysis

A child with ambiguous genitalia, brought up phenotypically male, had a 46,XX/46,XY karyotype. At laparotomy, he had a left sided ovary and uterus, and a right sided scrotal testis. The 46,XX line made up 50% of cells in the blood and 90% of cells in a skin biopsy. There were no cytogenetic polymorphisms. Analysis of lymphocyte DNA with seven polymorphic DNA markers showed him to be chimaeric, with four, three, and two parental alleles at different loci. He had one paternal and one maternal X chromosome at the marker DXS1053. Based on our data, we would suggest that chimaerism arose as a result of postzygotic fusion of two embryos. We have shown by DNA polymorphisms the presence of autosomal chimaerism in a case of sex chromosome chimaerism, and indicated the usefulness of DNA polymorphisms in determining the origin of chimaerism.

Case of 46,XX/47,XY, +21 chimerism in a newborn infant with ambiguous genitalia

We describe whole-body chimerism in a newborn infant with small phallus, pseudo-vaginal perineal hypospadias, and a bifid scrotum containing gonads. The human testis determining factor gene (SRY) was detected by PCR amplification. GTG-banding chromosome analysis in peripheral blood lymphocytes and cultured fibroblasts derived from right cubital skin showed a 46,XX/47,XY, +21 karyotype. Their ratios in each cell line were 294:5 and 178:7, respectively. QFQ-banding chromosome analysis documented 3 heteromorphic satellites on trisomic chromosomes 21 in the 47,XY, +21 cell line and a homozygous satellite pattern in the 46,XX cell line. Heteromorphic patterns of chromosomes 4, 13, 14, and 22 were also different between the two cell lines. To our knowledge, such disomy/trisomy chimeras have not been described previously.

A genetic review of complete and partial hydatidiform moles and nonmolar triploidy

Complete and partial hydatidiform moles are genetically aberrant conceptuses. Usually, complete moles have 46 chromosomes (diploidy), all of paternal origin. Most partial moles have 69 chromosomes (triploidy), including 23 of maternal origin and 46 of paternal origin. Triploidy that involves 23 paternal chromosomes and 46 maternal chromosomes is not associated with molar placental changes and, rarely, can result in a live-born infant with multiple birth defects. Herein we review the mechanisms of fertilization that may produce these unbalanced sets of parental chromosomes and the role of genomic imprinting as a possible explanation for these clinical conditions.

Chimerism as the etiology of a 46,XX/46,XY fertile true hermaphrodite

OBJECTIVE

To determine the conceptional events resulting in a 46,XX/46,XY true hermaphrodite and to report the first pregnancy in a 46,XX/46,XY true hermaphrodite with an ovotestis.

DESIGN

Chromosome studies were performed on patient lymphocytes and fibroblasts. Red cell antigens, human leukocyte antigens, and presence of Y-chromosome deoxyribonucleic acid were analyzed. Findings were compared with parental and sibling blood group data.

SETTING

Genetics clinic and laboratories of a university hospital.

RESULTS

These studies demonstrated that our patient is a chimera, with dual maternal and paternal contributions. In addition, despite the presence of an ovotestis, she conceived and delivered a child.

CONCLUSIONS

The mechanism for chimerism in this case could be fertilization of (1) the secondary oocyte and first polar body; (2) the ovum and first polar body; (3) the ovum and second polar body; or (4) fusion of two embryos.

The Liverpool chimaera

A dispermic human chimaera is described who is a fertile female XX/XY chimaera. The chimaera was discovered due to anomalies found during routine antenatal testing. The patient had two red cell populations differing in three blood group systems; ABO, Rh and MN. Analysis of cultured lymphocytes showed 70% of cells to have the 46, XY male karyotype and analysis of cultured skin cells showed 30% of cells to have the 46, XY karyotype.

XX/XY chimerism encountered during prenatal diagnosis

46,XX/46,XY chimerism has previously been reported in patients with abnormal sexual development, and rarely in otherwise normal individuals. We report the first postnatally documented prenatal diagnosis of whole-body 46,XX/46,XY chimerism in humans, discovered by maternal age amniocentesis. The normal male phenotype in this child creates a dilemma in prenatal counselling, since genotypic male/female chimerism cannot be assumed to imply an abnormal sexual phenotype.

Unilateral true hermaphrodite with 46,XX/46,XY dispermic chimerism

A 13 year old female presented with ambiguous external genitalia, right inguinal ovotestis, left ovary, apparently normal Mullerian system, and absent Wolffian system. Cultured lymphocytes showed a 46,XX/46,XY karyotype. Histopathology of the gonads confirmed true hermaphroditism. The presence of two genetically different erythrocyte populations was observed. The findings suggested that the patient is a true hermaphrodite dispermic chimera.

Diagnostic approach to the newborn with ambiguous genitalia

When assessing an infant with ambiguous genitalia, there are some important points to remember: Do not delay the evaluation of a patient with ambiguous genitalia. A delay may expose the patient unnecessarily to a life-threatening situation, such as a salt-losing crisis associated with 21-hydroxylase deficiency or one of the testosterone biosynthetic defects. Also, it is unfair to expect the family to be able to deal emotionally with the uncertainty of unresolved gender assignment. Never perform a buccal smear. There is absolutely no indication for performing a buccal smear at any point in the evaluation of any patient with ambiguous genitalia. Use of a buccal smear to determine gender assignment was helpful decades ago, before analysis of human chromosomes was possible. With current cytogenetic methodologies that can detect chromosomal mosaicism and subtle abnormalities of the X and Y chromosomes, there is never an indication to perform a buccal smear. Never make a gender assignment on the basis of the appearance of the external genitalia alone. The chromosomal sex and gonadal sex need to be determined first. The parents' feelings regarding the desired sex of the child, gender identity and fertility need to be discussed. Once there are sufficient data, gender assignment can be made. Gender assignment should be made as soon as possible after birth, but absolutely should be made by 18 months of age, when children develop gender identity. Never equivocate in the assignment of gender. The parents and the physicians must be absolutely certain of the gender assignment and must view their decision as final. Follow-up visits with the family ideally include an assessment of their acceptance of the gender assignment of the child. If there is ambivalence, steps must be taken to identify the source of ambivalence and to clarify the issues.

Detection and interpretation of two different cell lines in triploid abortions

Among a series of 98 triploid abortions, there were four specimens with two cells lines. The detection of two clones was by Q-banding of chromosomes. Two of these four specimens were dizygotic twins, the third was either a mosaic or monozygotic twins with loss of a sex chromosome from one twin and the fourth was best explained as a chimaera which arose by fertilization of two female pronuclei by three sperms. These two unusual specimens had XYY sex chromosome complements which is rare among triploids. Two additional specimens were diagnosed clinically as possible twin pregnancies but only one cell line was identified from tissue culture. The frequency of twins was of the order of 1/33.

Blood group chimeras. A review

More than 70 spontaneous chimeric propositi in man are known. This review attempts to summarize the information given by 32 twin chimeras, 32 dispermic chimeras and 11 chimeras of unestablished type.

46,XX/46XY chromosome complement in amniotic fluid cell culture followed by the birth of a normal female child

Experience indicates that the most likely explanation for a mixture of 46,XX/46,XY cells in an amniotic fluid sample is that of maternal cell contamination and that a normal male child is to be expected at birth. We report the bith of a normal female child following prenatal diagnosis of such a mixture. Extensive postnatal studies failed to reveal an XY cell line. The possible sources of the XY cell line are discussed, as are the various techniques that were applied in an effort to discover it's origin. Cross-contamination of samples could be ruled out and there was no evidence of an unsuspected twin pregnancy. It is clear from this case that not all 46,XX/46,XY results obtained in amniotic fluid can be assumed to represent maternal cell contamination and some effort should be made to eliminate other potential sources for such a mixture.

Investigation of genetic markers in a true hermaphrodite with chi 46,XX/46,XY

We documented a new case of chi 46,XX/46,XY true hermaphroditism substantiated by the evaluation of chromosomal heteromorphism in banded preparations. The patient, a 12-year-old Japanese boy with ambiguous external genitalia, was seen because of abnormal breast development. Surgical exploration showed the right gonad to be an ovotestis and the left gonad to be an ovary. Cytogenetic studies revealed cell admixtures of 46,XX and 46,XY karyotypes in peripheral lymphocytes, skin fibroblasts, and gonadal fibroblasts. From the pedigree studies, the paternal double genetic contributions were evidenced by the differences of sex chromosomes and the blood group types for the ABO and MNSs systems in the two cell lines of the patient. The maternal double genetic contributions were confirmed by the inheritance of Q-fluorescent markers on chromosomes 13 and 22 and by alleles for the Kidd blood group system.

Polymorphic variants in human chromosome 15

We found eight polymorphic variants in human chromosome 15 using Q, C, Q-C and Ag-NOR staining methods. These variants included brightly or dully fluorescent pericentric segments and satellites, giant satellites, increased amounts of short arm hetrochromatin (ph+) and darkly (C band-positive) or lightly (C band-negative) Giemsa-stained pericentric Q-negative segments. These staining properties indicated that the entire short arm of 15 contained at least four distinct chromatin segments: Q-negative centromeric heterochromatin, a Q-variable distal segment, a Q-negative satellite stalk, and Q-variable satellites, in that order, from proximal to distal ends. The BrdU-Hoechst 33258-stained R bands (RBH) and high resolution G subbands were also studied for karyologic characterization of chromosome 15. Most of these variants were reported also in 13, but insufficiently documented in other D and G chromosomes. Together with polymorpic pericentric fluorochromes seen in 3 and 4, Yq, and nonpathogenic t(D;Yq), the pattern of these variants can be used as karyologic fingerprints for identification of each individual and his or her cell explants both in vivo and in vitro.