Sex-discordant monochorionic twins with blood and tissue chimerism

Monochorionic Diamniotic Twins with Sex Discordance: Case Series

Background and Clinical Significance: Ultrasonographic diagnosis of twin pregnancies has become routine, with chorionicity playing a crucial role in assessing associated risks. Traditionally, monochorionic (MC) twins were believed to derive from a single zygote, ensuring sex concordance. However, recent cases of dizygotic monochorionic (MCDZ) twins challenge this paradigm. In this paper, four cases of MCDZ twins with sex discordance are described. Case presentation: Case 1 and case 2 describe two spontaneous MC/diamniotic twin pregnancies in which sex discordance between twins was attributed to blood chimerism. Case 3 is about a MC/diamniotic twin pregnancy derived from a single blastocyst transfer after in vitro fertilization (IVF), and that was complicated by twin-to-twin transfusion syndrome, with zygosity testing confirming the dizygosity. Case 4 is a twin anemia polycythemia sequence diagnosed after birth in twins considered dichorionic during pregnancy (due to sex difference) and defined as monochorionic after placental examination. Conclusions: The prevalence of monochorionic dizygotic (MCDZ) twins remains uncertain, and many cases likely go unnoticed, particularly when twins are of the same sex. In twin pregnancies, determining chorionicity during the first-trimester ultrasound (US) is critical. Accurate identification of monochorionicity is essential for managing potential complications. Careful verification of sex concordance between twins is necessary. In cases of sex discordance, amniocentesis is required for karyotype evaluation and zygosity testing.

Body-wide chimerism and mosaicism are predominant causes of naturally occurring ABO discrepancies

Routine ABO blood group typing of apparently healthy individuals sporadically uncovers unexplained mixed-field reactions. Such blood group discrepancies can either result from a haematopoiesis-confined or body-wide dispersed chimerism or mosaicism. Taking the distinct clinical consequences of these four different possibilities into account, we explored the responsible cause in nine affected individuals. Genotype analyses revealed that more than three-quarters were chimaeras (two same-sex females, four same-sex males, one sex-mismatched male), while two were mosaics. Short tandem repeat analyses of buccal swab, hair root and nail DNA suggested a body-wide involvement in all instances. Moreover, genome-wide array analyses unveiled that in both mosaic cases the causative genetic defect was a unique copy-neutral loss of heterozygosity encompassing the entire long arm of chromosome 9. The practical transfusion- or transplantation-associated consequences of such incidental discoveries are well known and therefore easily manageable. Far less appreciated is the fact that such findings also call attention to potential problems that directly ensue from their specific genetic make-up. In case of chimerism, these are the appearance of seemingly implausible family relationships and pitfalls in forensic testing. In case of mosaicism, they concern with the necessity to delineate innocuous pre-existent or age-related from disease-predisposing and disease-indicating cell clones.

Whole-genome sequences reveal zygotic composition in chimeric twins

While most dizygotic twins have a dichorionic placenta, rare cases of dizygotic twins with a monochorionic placenta have been reported. The monochorionic placenta in dizygotic twins allows in utero exchange of embryonic cells, resulting in chimerism in the twins. In practice, this chimerism is incidentally identified in mixed ABO blood types or in the presence of cells with a discordant sex chromosome. Here, we applied whole-genome sequencing to one triplet and one twin family to precisely understand their zygotic compositions, using millions of genomic variants as barcodes of zygotic origins. Peripheral blood showed asymmetrical contributions from two sister zygotes, where one of the zygotes was the major clone in both twins. Single-cell RNA sequencing of peripheral blood tissues further showed differential contributions from the two sister zygotes across blood cell types. In contrast, buccal tissues were pure in genetic composition, suggesting that in utero cellular exchanges were confined to the blood tissues. Our study illustrates the cellular history of twinning during human development, which is critical for managing the health of chimeric individuals in the era of genomic medicine.

Rare spontaneous monochorionic dizygotic twins: a case report and a systematic review

BACKGROUND

Monochorionic dizygotic twins are a rare condition, mostly related to assisted reproductive technology. This type of twinning is burdened by the same risk of pregnancy complications found in monochorionic monozygotic pregnancies.

CASE PRESENTATION

We report a case of spontaneous monochorionic dizygotic twins sharing situs inversus abdominalis and isolated levocardia, with only one twin affected by biliary atresia with splenic malformation syndrome. We also conducted a literature review of the 14 available documented monochorionic dizygotic twin gestations spontaneously conceived.

CONCLUSIONS

It is still unclear how this unusual type of twinning can occur in spontaneous conception. The evidence so far suggest the importance to timely diagnose the chorionicity, in order to adequately manage the typical complications associated with monochorionicity.

Case Report: Identification of Germline Chimerism in Monochorionic Dizygotic Twins

Monochorionic twins are generally considered to be monozygotic, as monochorionic dizygotic (MCDZ) twins are extremely rare in natural pregnancies. Several studies have reported this rare occurrence, and most of these pregnancies have been conceived by assisted reproductive technology (ART). These reports mostly focused on MCDZ twin pregnancies and the childhood development of the twins; a follow-up into adulthood and the effect on their reproduction has not been reported. In this case study, we report a case of chimerism in opposite-sex MCDZ twins who were naturally conceived and have reached reproductive maturity. We collected oral mucosal, endometrial, and germ cells from the twins and evaluated their chimerism using single-nucleotide polymorphism (SNP) array and droplet digital PCR (ddPCR). The SNP array showed that they had 4,049 non-allele shared loci, and they inherited nearly 50% informative SNP loci from each parent, confirming that they are dizygotic twins. We found that the female twin had a 46, XX (2)/46, XY (78) karyotype in her peripheral blood. The SNP array confirmed that the female twin and male twin had the same blood haplotype. The ddPCR result showed 92.84 (± 1.80%) chimerism in her blood. In case of chimerism in her germline, the female twin chose preimplantation genetic testing for aneuploidy for her blastocysts. Fortunately, the patient only had blood chimerism. A healthy boy was born at 39 weeks of gestation.

On the origin of zygosity and chorionicity in twinning: evidence from human in vitro fertilization

Assisted reproduction is presumed to increase monozygotic twin rates, with the possible contribution of laboratory and medical interventions. Monozygotic dichorionic gestations are supposed to originate from the splitting of an embryo during the first four days of development, before blastocyst formation. Single embryo transfers could result in dichorionic pregnancies, currently explained by embryo splitting as described in the worldwide used medical textbooks, or concomitant conception. However, such splitting has never been observed in human in vitro fertilization, and downregulated frozen cycles could also produce multiple gestations. Several models of the possible origins of dichorionicity have been suggested. However, some possible underlying mechanisms observed from assisted reproduction seem to have been overlooked. In this review, we aimed to document the current knowledge, criticize the accepted dogma, and propose new insights into the origin of zygosity and chorionicity.

The mystery of monozygotic twinning II: What can monozygotic twinning tell us about Amyoplasia from a review of the various mechanisms and types of monozygotic twinning?

Monozygotic (MZ) twins ("identical twins") are essentially unique to human beings. Why and how they arise is not known. This article reviews the possible different types of MZ twinning recognized in the previous article on twins and arthrogryposis. There appear to be at least three subgroups of MZ twinning: spontaneous, familial, and those related to artificial reproductive technologies. Each is likely to have different etiologies and different secondary findings. Spontaneous MZ twinning may relate to "overripe ova." Amyoplasia, a specific nongenetic form of arthrogryposis, appears to occur in spontaneous MZ twinning and may be related to twin-twin transfusion.

Chimerism involving a RB1 pathogenic variant in monochorionic dizygotic twins with twin-twin transfusion syndrome

We report the first case of blood chimerism involving a pathogenic RB1 variant in naturally conceived monochorionic-dizygotic twins (MC/DZ) with the twin-twin-transfusion syndrome (TTTS), presumably caused by the exchange of stem-cells. Twin A developed bilateral retinoblastoma at 7 months of age. Initial genetic testing identified a de novo RB1 pathogenic variant, with a 20% allelic ratio in both twins' blood. Subsequent genotyping of blood and skin confirmed dizygosity, with the affected twin harboring the RB1 pathogenic variant in skin and blood, and the unaffected twin carrying the variant only in blood.

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.

Chimerism in health and potential implications on behavior: A systematic review

In this review, we focus on the phenomenon of chimerism and especially microchimerism as one of the currently underexplored explanations for differences in health and behavior. Chimerism is an amalgamation of cells from two or more unique zygotes within a single organism, with microchimerism defined by a minor cell population of <1%. This article first presents an overview of the primary techniques employed to detect and quantify the presence of microchimerism and then reviews empirical studies of chimerism in mammals including primates and humans. In women, male microchimerism, a condition suggested to be the result of fetomaternal exchange in utero, is relatively easily detected by polymerase chain reaction molecular techniques targeting Y-chromosomal markers. Consequently, studies of chimerism in human diseases have largely focused on diseases with a predilection for females including autoimmune diseases, and female cancers. We detail studies of chimerism in human diseases and also discuss some potential implications in behavior. Understanding the prevalence of chimerism and the associated health outcomes will provide invaluable knowledge of human biology and guide novel approaches for treating diseases.

Is there a relationship between fetal sex and placental pathological characteristics in twin gestations?

Background

Placenta plays a central role in mediating growth and development of fetuses. Sex-specific placentas may complicate this role.

Methods

The study aimed at investigating the association between fetal sex and placental pathological findings in twin gestations using generalized estimating equation modeling. We used a large population-based clinical data born in British Columbia (BC) and linked the fetal-maternal data to hand-searched pathology reports of 1493 twin placentas from twins born in BC Women hospital. We analyzed the data using generalized estimating equations taking the cluster nature of twins into consideration.

Results

About 26.5% of twins were monochorionic and 73.5% were dizygotic. Most twins were male (51.3%). About 2/3 of twins were sex concordant (66.6%). Of the sex concordant twins, similar percentages were male-male (34.7%) and female-female (31.2%). Of the sex discordant twins, the male-female (33.3%) group constituted about 1/3 of the whole population.

Adjusted for chorionicity, birth weight discordance ≥30% and gestational age, the odds of chorionitis (1.38, 95% CI = 1.04–1.84), anastomosis (1.63, 95% CI = 1.22–2.19), unequal sharing of placenta (1.72, 95% CI = 1.11–2.64), placental inflammation (1.30, 95% CI = 1.05–1.62) and lesions (1.83, 95% CI = 1.02–3.31) were higher in male twins compared with females. Twins of either sex from sex-discordant pairs were less likely to have placental anastomosis compared to the reference category. Males from male-male pairs had higher odds of unequal placental sharing (74% higher) and composite inflammation (52% higher) compared with the reference twins.

Conclusion

Our findings suggest a relationship between sex and placental pathological results.

Unusual Twinning Resulting in Chimerism: A Systematic Review on Monochorionic Dizygotic Twins

Traditionally, it is understood that dizygotic (DZ) twins always have a dichorionic placenta. However, with 8% blood chimerism in DZ twins, placental sharing is probably more common than previously has been recognized. In this article, we will review all available cases of monochorionic dizygotic (MCDZ) twins. A total of 31 twins have been described in literature. A monochorionic diamniotic placenta is reported in all cases. Assisted reproductive technology is responsible for the origin of the pregnancy in 82.1% of the cases. In 15.4% of the sex-discordant twins, a genital anomaly was reported in one of the twins. Chimerism is demonstrable in 90.3% of the twins, leading to various diagnostic difficulties. As this review shows that most MCDZ twins are discovered by accident, it can be argued that it is far more common than has been assumed until now. However, the prevalence is still unclear. Awareness of MCDZ twinning is important, with subsequently correct medical strategies. Similarly, the resulting (blood) chimerism is essential to consider in diagnostic procedures, pre- and postnatally. More research on the effect of placental transfusion between sex-discordant twins is required.

Overview of genetics of disorders of sexual development

PURPOSE OF REVIEW

Disorders of sexual development (DSD) are a genetic and phenotypic heterogeneous group of congenital disorders. This review focuses on the genetics of DSD and aims to recognize and contextualize, in a systematic way, based on the classification and the genetic mechanisms, the latest developments in the field of DSD diagnostics.

RECENT FINDINGS

Due to the current diagnostic armamentarium, during the past decade, the field of DSD diagnostics has changed dramatically from the recognition of few genes and cytogenetic abnormalities, to the identification of multiple genes and a wide arrange of genetic mechanisms involved in the genesis of DSD. In addition, the phenotypes associated with the genetic mechanism have expanded tremendously.

SUMMARY

Despite the current diagnostic limitations, the landscape for genetics of DSD is encouraging due to discovery of new genes, their interactions, and the recognition of the variety of mechanisms involved.

Zygosity Diagnosis: When Physicians and DNA Disagree

Physicians and other medical professionals do not always provide new parents with an accurate diagnosis of their twins' zygosity. An overview of this problem is presented, supplemented by an interview with a mother who recently learned that her 2-year-old 'dizygotic (DZ)' twin girls are actually 'monozygotic (MZ)'. Reviews of two case studies, one of twins with sex-discordance and chimerism and the other of twins with congenital amegakaryotic thrombocytopenia, follow. Two additional studies, one a twin analysis of attractiveness to mosquitoes and the other a study of twins coping with crisis, are also described. Several articles and letters from the popular media, concerning less favored twins, paternity issues surrounding superfecundation, twins with late-onset Tay-Sachs disease, and triplets admitted to MIT are informative and insightful.