Prenatal diagnosis and normal outcome of a 46,XX/46,XY chimera: A Case Report

Clinical spectrum of female genital malformations in prenatal diagnosis

Introduction

Fetal genital malformations represent a rare and heterogeneous group of congenital malformations of the disorders of sexual development (DSD) spectrum.

Methods

A thorough literature review on the main topics in the prenatal approach towards DSD was conducted.

Results

First, a thorough overview on prenatal characteristics of the most common fetal genital malformations of ovaries, uterus and external genitalia, and second, a standardized approach for differential diagnosis in the presence of direct and indirect prenatal signs of DSDs.

Conclusions

This review is mainly directed towards the aspects of female genital malformations with  aspects of male DSD explained as well to aid in the prenatal differential diagnosis.

Chimerism 47,XY, + 8/46,XX: Follow-up for 11 Years

Approximately 30 sex chromosome discordant chimera cases have been reported to date. In particular, there are few reported cases of chimerism involving coexisting normal and abnormal lineages that each carries a distinct sex chromosome complement. To our knowledge, this is the first case of sexual chimerism with a simultaneous chromosomal aneuploidy involving chromosome 8. This report represents the data from 11 years of follow-up.

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 a parthenogenetic 46,XX/46,XY chimera presenting ambiguous genitalia

Sex-chromosome discordant chimerism (XX/XY chimerism) is a rare chromosomal disorder in humans. We report a boy with ambiguous genitalia and hypospadias, showing 46,XY[26]/46,XX[4] in peripheral blood cells. To clarify the mechanism of how this chimerism took place, we carried out whole-genome genotyping using a SNP array and microsatellite analysis. The B-allele frequency of the SNP array showed a mixture of three and five allele combinations, which excluded mosaicism but not chimerism, and suggested the fusion of two embryos or a shared parental haplotype between the two parental cells. All microsatellite markers showed a single maternal allele. From these results, we concluded that this XX/XY chimera is composed of two different paternal alleles and a single duplicated maternal genome. This XX/XY chimera likely arose from a diploid maternal cell that was formed via endoduplication of the maternal genome just before fertilization, being fertilized with both X and Y sperm.

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.

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.

Monochorionic dizygotic twins with discordant sex and confined blood chimerism

Monochorionic (MC) pregnancy in humans is usually considered to be associated only with monozygotic twinning. However, several reports have revealed that dizygotic (DZ) twins can also share a chorion during pregnancy. A chimera is defined as an organism that contains different cells derived from two or more distinct zygotes. As artificial reproductive techniques develop, it can be predicted that the occurrence of MC DZ twins will increase, and DNA-fingerprinting methods, such as short tandem repeat (STR) analysis, will be essential for their accurate diagnosis. We report the first Korean case of MC DZ twins with blood chimerism, 46,XX/46,XY, as a consequence of in vitro fertilization/embryo transfer. The clinical phenotypes of the twins' genitalia were complete female and male, respectively. Monochorionicity was confirmed by pathological analysis of the placenta after delivery. The dizygosity and confined blood chimerism of the twins were confirmed by STR analysis using their peripheral lymphocytes and skin fibroblasts. The confined blood chimerism of the twins can be considered similar to the status of the hematopoietic system in patients after allogenic bone marrow transplantation.

CONCLUSION

When MC twins with discordant sex are expected during pregnancy, it is important to consider the possibility of DZ twins showing normal sexual development, especially in twins who were fertilized using artificial reproductive techniques.

The identification of a spontaneous 47, XX, +21/46, XY chimeric fetus with male genitalia

Background

Approximately 30 sex-chromosome discordant chimera cases have been reported to date, of which only four cases carried trisomy 21. Here, we present an additional case, an aborted fetus with a karyotype of 47,XX, +21/46,XY.

Case presentation

Autopsy demonstrated that this fetus was normally developed and had male genitalia. Major characteristics of Down syndrome were not observed except an enlarged gap between the first and second toes. Karyotyping of tissues cultured from the fetus revealed the same chimeric chromosomal composition detected in the amniotic fluid but with a different ratio of [47,XX,+21] to [46,XY]. Further short tandem repeat analysis indicated a double paternal contribution and single maternal contribution to the fetus, with the additional chromosome 21 in the [47,XX,+21] cell lineage originating from the paternal side.

Conclusion

We thus propose that this chimeric fetus was formed via the dispermic fertilization of a parthenogenetic ovum with one (Y) sperm and one (X,+21) sperm.

Rare case of XX/XY mosaicism and trisomy 13 in early prenatal diagnosis

Coexistence of XX/XY sex mosaicism and autosomal trisomy in prenatal diagnosis is particularly rare. Herein, we report the first, to our knowledge, case of a fetus with cyclopia, ambiguous genitalia and a 47,XX,+13,inv9[47]/47,XY,+13[13] karyotype detected at 13 weeks of gestation after chorionic villus sampling. Molecular analysis after prenatal diagnosis suggests that this is a case of sex mosaicism coexisting with trisomy 13, rather than chimera.

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.

Rapid aneuploidy detection with multiplex ligation-dependent probe amplification: a prospective study of 4000 amniotic fluid samples

The introduction of prenatal screening requires rapid high-throughput diagnosis of common aneuploidies. Multiplex ligation-dependent probe amplification (MLPA) allows for quick, easily automated multiplex testing of these aneuploidies in one polymerase chain reaction. We performed a large prospective study using MLPA on 4000 amniotic fluid (AF) samples including all indications and compared its value to karyotyping and fluorescence in situ hybridization (FISH). MLPA can reliably determine common aneuploidies with 100% sensitivity and 100% specificity. Moreover, some mosaic cases and structural chromosome aberrations were detected as well. In cases of a male fetus, triploidies can be detected by an aberrant pattern of probe signals, which mimics maternal cell contamination (MCC). Macroscopic blood contamination was encountered in 3.2% of the AF samples. In 20% of these samples, an MLPA pattern was found consistent with MCC, although there were no false negatives of the most common aneuploidies. As the vast majority of inconclusive results (1.7%) is due to potential MCC, we designed a protocol in which we determine whether MLPA can be performed on blood-contaminated AF samples by testing if blood is of fetal origin. Then, the number of inconclusive results could be theoretically reduced to 0.05%. We propose an alternative interpretation of relative probe signals for rapid aneuploidy diagnosis (RAD). We discuss the value of MLPA for the detection of (submicroscopic) structural chromosome anomalies. MLPA is a reliable method that can replace FISH and could be used as a stand-alone test for RAD instead of karyotyping.