46,XX/46,XY chimerism in a phenotypically normal man

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.

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.

A case of 46,XX/46,XX chimerism in a phenotypically normal woman

Chimerism is the presence of two genetically different cell lines within a single organism, which is rarely observed in humans. Usually, chimerism in the human body is revealed by the finding of an abnormal phenotype during a medical examination or is unexpectedly detected in routine genetic analysis. However, the incidence or underlying mechanism of chimerism remains unclear due to the lack of information on this infrequent biological event. A phenotypically normal woman with a 46,XX karyotype and atypical short tandem repeat (STR) allelic patterns observed in DNA analysis was investigated with various genetic testing methods, including STR typing based on capillary electrophoresis and massively parallel sequencing, genome-wide SNP array, and a differentially methylated parental allele assay (DMPA). The proband's parents were not available for testing to discriminate the parental allelic contribution, but the parents' alleles were recovered from testing the proband's siblings. Based on the results consistently found in multiple analyses using STR and single nucleotide polymorphism (SNP) polymorphism markers, dispermic fertilization was suggested as the underlying mechanism. The application of various molecular genetic testing methods was used to elucidate the chimerism observed in the proband in this study. In the future, the development of novel genetic markers or techniques, such as DMPA, may have potential use in the investigation of chimerism.

Unusual finding in the karyotype of a neonate with glandular hypospadias with chordee

A 37-week, 2700 g vaginally delivered baby was admitted for respiratory distress which was attributed to transient tachypnoea of newborn. A clinical finding of glandular hypospadias with ventral chordee was detected. The penis was normal in size, and gonads were palpable bilaterally in the scrotal sac. The parents were informed of the good prognosis associated with this milder variety of hypospadias. In view of parental concerns, a fluorescent in situ hybridisation (FISH) for X and Y chromosome was performed. Surprisingly, FISH revealed the presence of 46, XY in 90% of cells and 46, XX in 10% of the remainder cells suggesting a diagnosis of chimerism.

Tri-allelic expression of HLA gene in 46,XX/46,XY chimerism

INTRODUCTION

Chimerism is defined as coexistence of different cell lines in an individual. 46,XX/46,XY chimerism is very rare and exhibits broad range of clinical phenotypes. Most cases are detected at infancy or younger age due to disorders of sex development, while phenotypically normal cases are incidentally discovered through abnormal blood grouping results or multiple genotypes in HLA.

OBJECTIVE

Aim was to determine the genetic expression of numerous HLA alleles detected in phenotypically normal 46,XX/46,XY chimerism.

MATERIALS AND METHODS

A patient was admitted for lung transplantation due to end-stage pulmonary disease. Pre-transplantation work-up included blood group typing and HLA DNA typing analyses. Peripheral blood and hair follicle specimens were used to confirm unusual tri-allelic results by high-resolution PCR-SBT. Cytogenetic analyses of karyotyping, FISH and chromosomal microarray were done. Flowcytometry crossmatch analysis was conducted using lymphocytes and anti-HLA sera defined by Luminex panel reactive antibody test (One Lambda, Inc., Canoga Park, CA), to determine antigen expression of HLA alleles.

RESULTS

46,XX/46,XY chimerism was confirmed through series of cytogenetic analyses. HLA typing of the patient revealed three alleles from HLA-A, -B and -DRB1 loci. Antigen expression of all 3 HLA alleles was confirmed by flow cytometry crossmatch.

DISCUSSION

A case of normal phenotype 46,XX/46,XY chimerism was detected for the first time in Korean patient admitted for lung transplantation. Cytogenetic results were confirmatory for chimerism and HLA typing using PCR-SBT method was able to detect the presence of 3 HLA alleles. Flowcytometry crossmatch was proven sensitive for detecting antigen expression of different cell lines of small proportions.

Clinical and Genetic Analysis of an Infertile Male with 46,XX/46,XY Chimerism

The sex chromosome-discordant chimerism 46,XX/46,XY is rarely found in humans with a phenotypically normal appearance, and this lack of phenotypic changes and the rarity of chimerism make it difficult to identify its exact incidence. Here, we report a case of this sex chromosome-discordant chimerism diagnosed by cytogenic and molecular analyses of peripheral blood in a phenotypically normal male who was referred to our facility for infertility. Based on the karyotype, fluorescence in situ hybridisation (FISH) and short tandem repeat (STR) analyses, the type of this chimerism was determined to be tetragametic presenting four alleles at two loci on chromosomes 16 and 21.

Case of successful IVF treatment of an oligospermic male with 46,XX/46,XY chimerism

INTRODUCTION

We present a case of an infertile male with 46,XX/46,XYchimerism fathering a child after ICSI procedure.

METHODS

Conventional cytogenetic analysis on chromosomes, derived from lymphocytes, using standard Q-banding procedures with a 450-550-band resolution and short-tandem-repeat analysis of 14 loci.

RESULTS

Analysis of 20 metaphases from lymphocytes indicated that the proband was a karyotypic mosaic with an almost equal distribution between male and female cell lines. In total, 12 of 20 (60%) metaphases exhibited a normal female karyotype 46,XX, while 8 of 20 (40%) metaphases demonstrated a normal male karyotype 46,XY. No structural chromosomal abnormalities were present. Out of 14 STR loci, two loci (D18S51 and D21S11) showed four different alleles in peripheral blood, buccal mucosal cells, conjunctival mucosal cells, and seminal fluid. In three loci (D2S1338, D7S820, and vWA), three alleles were detected with quantitative differences that indicated presence of four alleles. In DNA extracted from washed semen, four alleles were detected in one locus, and three alleles were detected in three loci. This pattern is consistent with tetragametic chimerism. There were no quantitative significant differences in peak heights between maternal and paternal alleles. STR-analysis on DNA from the son confirmed paternity.

CONCLUSION

We report a unique case with 46,XX/46,XY chimerism confirmed to be tetragametic, demonstrated in several tissues, with male phenotype and no genital ambiguity with oligospermia fathering a healthy child after IVF with ICSI procedure.

A case of maternal-foetal chimerism identified during routine histocompatibility testing for hematopoietic stem cell transplantation

This report describes a case of maternal-foetal chimerism identified in a boy diagnosed with SCID, who underwent HLA testing in preparation for HSCT. The first analysis was carried out on DNA from peripheral blood and included HLA-A, HLA-B, HLA-DRB1 typing using PCR-SSO. The patient's HLA-B typing results were noninterpretable. All samples were re-typed for HLA-B using PCR-SSP, again resulting in noninterpretable typing of patient's HLA-B. In both cases, several weak positive probes/reactions interfered with the interpretation when using commercial software. Next round of HLA typing, using PCR-SSP and PCR-SSO methods, included the patient's bone marrow sample and HLA-C locus, but interpretation was again not possible. The PCR-STR analysis performed on both peripheral blood and bone marrow samples revealed seven STRs for which two maternal and one paternal allele were detected. Retrospective manual interpretation of HLA-B and HLA-C typing revealed that weak positive reactions were indeed owed to paternal HLA-B and HLA-C alleles and that the patient had both maternal and one paternal allele. Retyping of HLA-B and HLA-C loci and STR analysis on the patient's buccal cells sample revealed the expected one maternal/one paternal allele pattern. In summary, the combination of several different typing methods and manual interpretation were necessary to obtain the patient's HLA typing results.

Uniparental Disomy in Somatic Mosaicism 45,X/46,XY/46,XX Associated with Ambiguous Genitalia

Disorders of sex development (DSD) affect the development of chromosomal, gonadal and/or anatomical sex. We analyzed a patient with ambiguous genitalia aiming to correlate the genetic findings with the phenotype. Blood and tissue samples from a male patient with penoscrotal hypospadias were analyzed by immunohistochemistry, karyotyping and FISH. DNA was sequenced for the AR, SRY and DHH genes, and further 26 loci in different sex chromosomes were analyzed by MLPA. The gonosomal origin was evaluated by simple tandem repeat (STR) analysis and SNP array. Histopathology revealed a streak gonad, a fallopian tube and a rudimentary uterus, positive for placental alkaline phosphatase, cytokeratin-7 and c-kit, and negative for estrogen, androgen and progesterone receptors, alpha-inhibin, alpha-1-fetoprotein, β-hCG, and oct-4. Karyotyping showed a 45,X/46,XY mosaicism, yet FISH showed both 46,XX/46,XY mosaicism (gonad and urethral plate), 46,XX (uterus and tube) and 46,XY karyotypes (rudimentary testicular tissue). DNA sequencing revealed intact sequences in SOX9, WNT4, NR0B1, NR5A1, CYP21A2, SRY, AR, and DHH. STR analysis showed only one maternal allele for all X chromosome markers (uniparental isodisomy, UPD), with a weaker SRY signal and a 4:1 ratio in the X:Y signal. Our findings suggest that the observed complex DSD phenotype is the result of somatic gonosomal mosaicism and UPD despite a normal blood karyotype. The presence of UPD warrants adequate genetic counseling for the family and frequent, lifelong, preventive follow-up controls in the patient.

[Blood cell chimerism in dizygotic twins conceived by in vitro fertilization]

We present a case of hematopoietic chimerism in dizygotic twins (male and female) conceived by in vitro fertilization (IVF). At 8 years of age a blood karyotype was performed on the female due to the presence of clitoromegaly. Two different lines: 46,XX (53%) and 46,XY (47%) were found. FISH studies confirmed the presence of the SRY gene in 46,XY cells. Karyotyping of the male showed two different lines: 46,XY (58%) and 46,XX (42%). SRY gene was present in 46,XY cells. Microsatellite analyses of blood DNA revealed tetra-allelic contribution at some autosomal loci with similar proportions of maternal and paternal alleles and X/Y chromosome dose. FISH in buccal mucous showed that all cells from the female were 46,XX and those from the male 46,XY. The gonadal karyotype in the female was 46,XX without SRY. Hence, we report 46,XX/46,XY chimerism in dizygotic twins. Blood chimerism was confirmed by performing FISH on the buccal cells of the patients.

Blood chimerism in a dizygotic dichorionic pregnancy

Blood chimerism in twins is known to occur through the transfer of hematopoietic stem cells between the fetuses via a common placenta. We present a case of blood chimerism in a dizygotic dichorionic twin pregnancy. The female twin was delivered at 34 weeks of gestation, and the male twin was stillborn. Pathologic examination confirmed dichorionic diamniotic placentas. The karyotype of the female child was obtained using peripheral blood sample, and it revealed a mixture of 46,XX and 46,XY cells (chi 46,XY[13]/46,XX[7]). FISH analysis performed on the buccal cells by using CEP X/Y probe (Abbott Molecular Inc., USA) revealed 100% XX signals (nuc ish Xcen(DXZ1x2)[500]). Gross examination of the external genitalia and abdominal ultrasonography revealed no definitive abnormal findings in relation to sex differentiation. When XX/XY chimerism is present in blood lymphocytes, careful examination of external genitalia and reproductive organs and further studies are required to detect chimerism in non-hematopoetic tissues. This is a rare case of blood chimerism in dichorionic placentas, in contrast to those in monochorionic placentas.

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.

Different rates of telomere attrition in peripheral lymphocytes in a pair of dizygotic twins with hematopoietic chimerism

Hematopoietic chimerism in dizygotic twins is due to placental vascular anastomoses and arises when hematopoietic stem cells from one twin home to the bone marrow of the other. We report a case of hematopoietic chimerism in a pair of 27-year-old dizygotic twins who each had a mixture of 46,XX and 46,XY blood lymphocytes, both with 98% male (XY) lymphocytes and 2% female (XX) lymphocytes. Analysis of telomere length by T/C FISH revealed that the female twin generally had longer telomeres than the male twin. Moreover, in the male sibling, the telomeres within the female lymphocytes were shortened to 87% of their original length, while the telomeres within the male lymphocytes were 33% longer in the female sibling. Thus, telomere length attrition in peripheral lymphocytes is determined mainly by the environment of the cell and less by intracellular factors.

Chimera and other fertilization errors

The finding of a mixture of 46,XX and 46,XY cells in an individual has been rarely reported in literature. It usually results in individuals with ambiguous genitalia. Approximately 10% of true human hermaphrodites show this type of karyotype. However, the underlying mechanisms are poorly understood. It may be the result of mosaicism or chimerism. By definition, a chimera is produced by the fusion of two different zygotes in a single embryo, while a mosaic contains genetically different cells issued from a single zygote. Several mechanisms are involved in the production of chimera. Stricto sensu, chimerism occurs from the post-zygotic fusion of two distinct embryos leading to a tetragametic chimera. In addition, there are other entities, which are also referred to as chimera: parthenogenetic chimera and chimera resulting from fertilization of the second polar body. Furthermore, a particular type of chimera called 'androgenetic chimera' recently described in fetuses with placental mesenchymal dysplasia and in rare patients with Beckwith-Wiedemann syndrome is discussed. Strategies to study mechanisms leading to the production of chimera and mosaics are also proposed.

Pulmonary lymphangioleiomyomatosis in a man

Pulmonary lymphangioleiomyomatosis (LAM) is an uncommon disease reported to occur exclusively in women. We describe a phenotypically normal man with pulmonary LAM. Fluorescence in situ hybridization (FISH) studies performed on the lung biopsy confirmed a normal XY genotype. Our patient also had stigmata of tuberous sclerosis complex (TSC), including facial angiofibromas and renal angiomyolipoma. Immunohistochemical stains of both LAM and renal angiomyolipoma showed positive immunoreactivity for hamartin (TSC1) and loss of immunoreactivity for tuberin (TSC2). Loss of heterozygosity (LOH) for TSC2 was further demonstrated in the renal angiomyolipoma. Coupled with the results of immunostains, these findings are consistent with TSC2 mutation.

Polymorphic detection of a parthenogenetic maternal and double paternal contribution to a 46,XX/46,XY hermaphrodite

True hermaphroditism in humans usually is associated with a 46,XX karyotype or with mosaicism in which admixtures of cells with an XX and an XY karyotype are seen. However, the mechanisms that cause such mosaicisms are poorly understood. To date, with rare exceptions, analyses of hermaphrodites have been limited mostly to cytogenetic investigations. In this report, we describe a 5-year-old patient with true hermaphroditism and a 46,XX/46,XY karyotype (ratio 38:12) in lymphocytes, suggesting involvement of two fertilization events. Microsatellite DNA polymorphisms distributed throughout the genome were analyzed, to investigate the origin of the cell lines concerned. The results are consistent with double paternal and single maternal genetic contributions. Possible mechanisms that would explain these findings are discussed. The most likely mechanism involves a single haploid ovum dividing parthenogenetically into two haploid ova, followed by double fertilization and fusion of the two zygotes into a single individual, at the early embryonic stage.

Confined placental chimerism: prenatal and postnatal cytogenetic and molecular analysis, and pregnancy outcome

The presence of two cell lines in chorionic villi sampling (CVS) represents a significant complication in CVS analysis, interpretation, and counseling. We report on the cytogenetic and molecular analysis of a pregnancy that was conceived on clomiphene citrate. Two cell lines (46,XX and 47,XY,+9) were discovered in CVS analysis done for maternal age; 94% of the cells in the culture were 46,XX and 6% were 47,XY, +9 (the direct preparation was 46,XX). As neither line could have derived from the other, chimerism and not mosaicism was suspected, with the 47,XY,+9 cells deriving from a co-twin whose demise was the result of the autosomal trisomy. At a subsequent amniocentesis, only normal female cells were observed and a normal female infant was delivered at term. Cytogenetic analysis done on the infant's peripheral blood and on a sample of an umbilical vessel showed only 46,XX cells, while amnion and a fibrotic area of the placenta contained 2 cell lines, 46,XX and 47,XY,+9. Molecular analysis of 3 different tissues was done by the polymerase chain reaction (PCR) and Southern blotting, using Y specific primers and probes, respectively. The presence of Y specific DNA was detected in the placenta and amnion, but not in the umbilical blood vessel. These data excluded true chimerism in the fetal tissues at the level of about 1 in 10(5) cells and have defined for the first time probable confined placental chimerism (CPC), the result most likely of a "vanishing twin." Whenever two cell lines are found in CVS, especially in the setting of pharmacologically stimulated ovulation, the possibility of CPC should be considered. The effects of CPC on placental function and fetal outcome merit further study.

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.