Chimera and other fertilization errors

Genetic counseling of mosaicism for balanced or unbalanced translocation with a normal cell line at amniocentesis

Genetic counseling of mosaicism for balanced translocation with a normal cell line at amniocentesis is not difficult because most of the reported cases have normal phenotypes. However, genetic counseling of mosaicism for unbalanced translocation with a normal cell line at amniocentesis remains difficult because cases with mosaic unbalanced translocation with a normal cell line at prenatal diagnosis have been reported to be associated with either normal or abnormal phenotype. This article makes a comprehensive review of the reported cases of de novo or familial mosaic unbalanced translocation with a normal cell line and various counseling issues such as meiotic event, post-zygotic mitotic event, culture artefact, chimerism, uniparental disomy (UPD), jumping translocation, cytogenetic discrepancy between cultured and uncultured amniocytes and among various tissues, perinatal progressive decrease of the unbalanced translocation cell line and a possible favorable fetal outcome. The information provided is useful for obstetricians and genetic counselors during genetic counseling of the parents who wish to keep the babies under such a circumstance.

Intersex Pretenders

False claims of having an intersex condition have been observed in print, video, Internet media, and in live presentations. Claims of being intersexed in publicly accessible media were examined and evidence that they were false was considered sufficiently conclusive in 37 cases. Falsity was most often detected due to medical implausibility and/or inconsistency, but sometimes also using information from third-party or published sources. The majority, 26/37, of cases were natal males; 11/37 were natal females. Almost all (34/37) were transgendered, living, or aspiring to live, in their non-natal sex or as socially intergender. The most commonly claimed diagnosis was ovotesticular disorder ("true hermaphroditism") due to chimerism, an actually uncommon cause of authentic intersexuality. Motivations for pretending to be intersexed were inferred from statements and behaviors and were varied. Some such pretenders appear to be avoiding the external or internalized stigma of an actual transgendered condition. Some appear, similarly to persons with factitious disorder, to be seeking attention and/or the role of a sick, disadvantaged, or victimized person. Some showed evidence of paraphilia, most frequently autogynephilia, and, in several cases, paraphilic diaperism. For some cases, such claims had been accepted as authentic by journalists or social scientists and repeated as true in published material.

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.

Molecular Analysis of Parthenogenetic Chimerism in a 46,XX/46,XY Patient with Idiopathic Oligoasthenoteratozoospermia

INTRODUCTION

Parthenogenetic chimera is an extremely rare condition in human. Very few patients with parthenogenetic chimerism with XX/XY cells have been identified.

CASE PRESENTATION

We report the clinical findings and molecular analysis of chimerism with a 46,XX/46,XY karyotype in a patient presenting idiopathic oligoasthenoteratozoospermia (OAT). To clarify the mechanism of chimera formation, short tandem repeat analysis using 21 loci was carried out. Quantitation of alleles in D6S1043, D12S391, fibrinogen alpha chain, and amelogenin revealed double paternal and one maternal genetic contribution to the patient, which is consistent with a parthenogenetic chimerism. The likely mechanism of chimerism formation was also discussed, followed by a literature review.

CONCLUSION

This is the first documented case of parthenogenetic chimerism in an adult male with XX/XY cells presenting OAT. Improved cell sampling and more sensitive and specific detection methods are necessary to identify more patients with XX/XY chimerism for systematic studies on this condition in the future.

Chromosome analysis of foetal tissue from 1903 spontaneous abortion patients in 5 regions of China: a retrospective multicentre study

BACKGROUND

Abnormal foetal tissue chromosome karyotypes are one of the important pathogenic factors for spontaneous abortion (SA). To investigate the age and abnormal foetal karyotypes of 1903 couples who experienced SA.

METHODS

A retrospective multicentre study collected age and foetal tissue karyotypes CNV-seq data of 1903 SA couples from 6 hospitals in 5 regions from January 2017 to March 2022. The distribution and correlation of abnormal foetal tissue karyotypes were evaluated by using regions and age.

RESULTS

In our study, 1140 couples (60.5% of the total) had abnormal foetal tissue chromosome karyotypes in all regions. We found that there were differences in the number of abnormal foetal tissue chromosome karyotypes, of which the incidence of trisomy was higher. At the same time, the populations situated in the eastern region had a more triploid (15.5%) distribution, trisomy (58.1%) in the southern region, mosaicism (14.8%) and microduplication (31.7%) in the southwestern region, microdeletion (16.7%) in the northern region. There are variances across areas, and it is more common in the north. The incidence risk of prenatal chromosomal abnormalities varied according to age group.

CONCLUSION

The findings of this study suggest that the karyotypes of patients with abnormal foetal tissue chromosome abortion in different regions were different. Meanwhile, patients ≥ 35 years old had a higher risk of abnormal foetal tissue chromosome abortion.

A Rare Case of Mosaic 3pter and 5pter Deletion-Duplication with Autism Spectrum Disorder and Dyskinesia

INTRODUCTION

There is evidence that neurodevelopmental disorders are associated with chromosomal abnormalities. Current genetic testing can clinch an exact diagnosis in 20-25% of such cases. Case Description. A 3 years and 11 months old boy with global developmental delay had repetitive behaviors and hyperkinetic movements. He was stunted and underweight. He had ataxia, limb dyskinesia, triangular face, microcephaly, upward slanting palpebral fissure, hypertelorism, retrognathia, posteriorly rotated ears, long philtrum, thin lips, broad nasal tip, polydactyly, tappering fingers, and decreased tone in the upper and lower limbs with normal deep tendon reflexes. Magnetic resonance imaging of the brain, ultrasound of the abdomen, and ophthalmological evaluation were normal. Brain evoked response auditory revealed bilateral moderate hearing loss. He fulfilled the Diagnostic Statistical Manual 5 criteria for autism. In the Vineland Social Maturity Scale, his score indicated a severe delay in social functioning. His genetic evaluation included karyotyping, fluorescence in situ hybridization (FISH), and chromosomal microarray analysis (CMA). The karyotype report from high-resolution lymphocyte cultures was mos 46, XY, der(3)t(3; 5)(p26; p15.3)[50]/46, XY,der(5) t(3;5) (p26;p15.3)[50].ish. His karyotype report showed a very rare and abnormal mosaic pattern with two cell lines (50% each). Cell-line#1: 3pter deletion with 5pter duplication (3pter-/5pter+) and cell-line#2: 3pter duplication with 5pter deletion (3pter+/5pter-) derived from a de novo reciprocal translocation t(3; 5)(p26; p15.3) which was confirmed by FISH. The chromosomal microarray analysis report was normal. The two cell lines (50% each) seem to have balanced out at the whole genome level. Occupational, sensory integration, and behavior modification therapy were initiated for his autistic features, and anticholinergic trihexiphenidyl was prescribed for hyperkinetic movements.

CONCLUSION

This case highlights a rare genetic finding and the need for timely genetic testing in a child with dysmorphism and autism with movement disorder to enable appropriate management and genetic counselling.

Case report: Molecular analysis of a 47,XY,+21/46,XX chimera using SNP microarray and review of literature

Chimerism is a very rare genetic finding in human. Most reported cases have a chi 46,XX/46,XY karyotype. Only three non-twin cases carrying both trisomy 21 and a normal karyotype have been reported, including two cases with a chi 47,XY,+21/46,XX karyotype and a case with a chi 47,XX,+21/46,XY karyotype. Herein we describe an additional case with a chi 47,XY,+21/46,XX karyotype. For the case, a physical examination at the age of 1 year revealed ambiguous genitalia with no features of Down syndrome or other malformations. Growth and developmental milestones were within normal ranges. We performed short tandem repeat (STR) and single nucleotide polymorphism (SNP) microarray analyses to attempt to identify the mechanism underlying the chimerism in this patient and the origin of the extra chromosome 21. Cytogenetic analyses of the patient's peripheral blood revealed approximately 17% of a 47,XY,+21 lineage by G-banding karyotype analysis, 13%-17% by FISH analyses of uncultured peripheral blood, and 10%-15% by SNP microarray analysis. Four years later, the percentage of trisomy 21 cells had decreased to approximately 6%. SNP microarray and STR analyses revealed a single maternal and double paternal genetic contribution to the patient for the majority of the markers, including the chromosome 21 markers. The extra chromosome 21 was paternally derived and meiosis I nondisjunction likely occurred during spermatogenesis. The mechanisms underlying chimera in our case was likely fertilization two spermatozoa, one with an ovum and the other with the second polar body.

Parental genomes segregate into distinct blastomeres during multipolar zygotic divisions leading to mixoploid and chimeric blastocysts

BACKGROUND

During normal zygotic division, two haploid parental genomes replicate, unite and segregate into two biparental diploid blastomeres.

RESULTS

Contrary to this fundamental biological tenet, we demonstrate here that parental genomes can segregate to distinct blastomeres during the zygotic division resulting in haploid or uniparental diploid and polyploid cells, a phenomenon coined heterogoneic division. By mapping the genomic landscape of 82 blastomeres from 25 bovine zygotes, we show that multipolar zygotic division is a tell-tale of whole-genome segregation errors. Based on the haplotypes and live-imaging of zygotic divisions, we demonstrate that various combinations of androgenetic, gynogenetic, diploid, and polyploid blastomeres arise via distinct parental genome segregation errors including the formation of additional paternal, private parental, or tripolar spindles, or by extrusion of paternal genomes. Hence, we provide evidence that private parental spindles, if failing to congress before anaphase, can lead to whole-genome segregation errors. In addition, anuclear blastomeres are common, indicating that cytokinesis can be uncoupled from karyokinesis. Dissociation of blastocyst-stage embryos further demonstrates that whole-genome segregation errors might lead to mixoploid or chimeric development in both human and cow. Yet, following multipolar zygotic division, fewer embryos reach the blastocyst stage and diploidization occurs frequently indicating that alternatively, blastomeres with genome-wide errors resulting from whole-genome segregation errors can be selected against or contribute to embryonic arrest.

CONCLUSIONS

Heterogoneic zygotic division provides an overarching paradigm for the development of mixoploid and chimeric individuals and moles and can be an important cause of embryonic and fetal arrest following natural conception or IVF.

Beyond the Microbiome: Germ-ganism? An Integrative Idea for Microbial Existence, Organization, Growth, Pathogenicity, and Therapeutics

The advances made by microbiome research call for new vocabulary and expansion of our thinking in microbiology. For example, the life-forms presenting in both unicellular and multicellular formats invite us to rethink microbial existence, organization, growth, pathogenicity, and therapeutics in the 21st century. A view of such populations as parts of single organisms with a loose, distributed multicellular organization, introduced here as a germ-ganism, rather than communities, might open up interesting prospects for diagnostics and therapeutics innovation. This study tested and further contextualized the concept of germ-ganism using solid cultures of bacteria and fungi. Based on our findings and the literature reviewed herein, we propose that germ-ganism has synergy with a systems medicine approach by broadening host-environment interactions from cells and microorganisms to a scale of biological ecosystems. Germ-ganism also brings about the possibility of studying the multilevel impacts of novel therapeutic agents within and across networks of microbial ecosystems. The germ-ganism would lend itself, in the long term, to a veritable biocybernetics system, while in the mid-term, we anticipate it will contribute to new diagnostics and therapeutics. Biosecurity applications would be immensely affected by germ-ganism. Industrial applications of germ-ganism are of interest as a more sustainable alternative to costly solutions such as tampered strains/microorganisms. In conclusion, germ-ganism is informed by lessons from microbiome research and invites rethinking microbial existence, organization, and growth as an organism. Germ-ganism has vast ramifications for understanding pathogenicity, and clinical, biosecurity, and biotechnology applications in the current historical moment of the COVID-19 pandemic and beyond.

De novo balanced reciprocal translocation mosaic t(1;3)(q42;q25) detected by prenatal genetic diagnosis: a fetus conceived using preimplantation genetic testing due to a t(12;14)(q22;q13) balanced paternal reciprocal translocation

INTRODUCTION

De novo balanced reciprocal translocations mosaicism in fetus conceived using preimplantation genetic testing from a different balanced translocation carrier parent has been rarely reported.

METHODS

Chromosomal microarray analysis, karyotype analysis and fluorescent in situ hybridization were performed to verify the type and heredity of the rearrangement. STR analysis was conducted to identify potential contamination and verify kinship. In addition, a local BLAST engine was performed to locate potentially homologous segments which might contribute to the translocation in breakpoints of chromosome.

RESULTS

A rare de novo balanced reciprocal translocations mosaicism mos 46,XY,t(1;3)(q42;q25)[40]/46,XY[39] was diagnosed in a fetus conceived using preimplantation genetic testing due to a 46,XY,t(12;14)(q22;q13) balanced translocation carrier father through multiplatform genetic techniques. Two of the largest continuous high homology segments were identified in chromosomal band 1q42.12 and 3q25.2. At the 21-months follow up, infant has achieved all psychomotor development milestones as well as growth within the normal reference range.

CONCLUSION

We present a prenatal diagnosis of a rare de novo balanced reciprocal translocations mosaicism in a fetus who conceived by preimplantation genetic testing. The most reasonable driving mechanism was that a de novo mitotic error caused by nonallelic homologous recombination between 1q42.12 and 3q25.2 in a zygote within the first or early cell divisions, which results in a mosaic embryo with the variant present in a half proportion of cells.

Androgenetic/Biparental Mosaic/Chimeric Conceptions With a Molar Component: A Diagnostic and Clinical Challenge

Hydatidiform moles (HM) are gestational trophoblastic diseases which arise due to an imbalance in genetic material and which are morphologically characterized by enlarged and irregular chorionic villi and trophoblastic hyperplasia, among other features. The morphologic differential diagnosis for HM encompasses a number of entities including androgenetic/biparental mosaic/chimeric (ABMC) conceptions, an interesting duo of lesions with a nonmolar form (placental mesenchymal dysplasia) and a molar form (typically with a complete HM component). ABMC conceptions contain a mixture of 2 cell populations (1 androgenetic and 1 biparental) and arise as a result of mosaicism (mitotic error in a zygote) or chimerism (fusion of 2 zygotes). Because of their unique molecular underpinnings, these rare lesions show a number of findings including the presence of multiple villous populations, discordant p57 immunostaining, and mixed genotypes. ABMC conceptions are important to accurately diagnose as the molar form in particular carries a risk for persistent gestational trophoblastic diseases and thus requires appropriate treatment and follow-up. In this report, we provide detailed characterizations of 2 such cases of ABMC conceptions with a molar component. Both patients (ages 34 and 31) were in the first trimester of pregnancy and had ultrasound findings concerning for HM. Increased comprehension of the pathogenesis and morphology of ABMC conceptions, combined with ancillary techniques including p57 immunohistochemistry, fluorescence in situ hybridization, and molar genotyping, has allowed us to accurately and efficiently identify these lesions. However, a number of pitfalls exist which may lead to misdiagnosis.

Horse Clinical Cytogenetics: Recurrent Themes and Novel Findings

Clinical cytogenetic studies in horses have been ongoing for over half a century and clearly demonstrate that chromosomal disorders are among the most common non-infectious causes of decreased fertility, infertility, and congenital defects. Large-scale cytogenetic surveys show that almost 30% of horses with reproductive or developmental problems have chromosome aberrations, whereas abnormal karyotypes are found in only 2-5% of the general population. Among the many chromosome abnormalities reported in the horse, most are unique or rare. However, all surveys agree that there are two recurrent conditions: X-monosomy and SRY-negative XY male-to-female sex reversal, making up approximately 35% and 11% of all chromosome abnormalities, respectively. The two are signature conditions for the horse and rare or absent in other domestic species. The progress in equine genomics and the development of molecular tools, have qualitatively improved clinical cytogenetics today, allowing for refined characterization of aberrations and understanding the underlying molecular mechanisms. While cutting-edge genomics tools promise further improvements in chromosome analysis, they will not entirely replace traditional cytogenetics, which still is the most straightforward, cost-effective, and fastest approach for the initial evaluation of potential breeding animals and horses with reproductive or developmental disorders.

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 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.

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.

Double Autosomal/Gonosomal Mosaic Trisomy 47,XXX/47,XX,+14 in a Newborn with Multiple Congenital Anomalies

Chromosomal trisomies are the most frequent major chromosomal anomalies in humans and can be present in a mosaic or a non-mosaic constitution. We report the first case of a newborn girl presenting with multiple congenital anomalies and a double mosaic trisomy involving chromosome 14 and the X chromosome detected by array CGH. Karyotype analysis revealed a double mosaic with 2 independent abnormal cell lines and the absence of 46,XX and 48,XXX,+14 cell lineages. The patient showed most of the clinical characteristics of mosaic trisomy 14. Analysis of autosomal DNA markers in the proband's blood sample did not support the presence of chimerism. Further analysis of chromosome X DNA markers suggests that the extra X chromosome most probably arose as a consequence of nondisjunction in meiosis II in the maternal lineage.

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.

Ten new cases of Balanced Reciprocal Translocation Mosaicism (BRTM): Reproductive implications, frequency and mechanism

Chromosomal anomalies are well known to be an important cause of infertility, sterility and pregnancy loss. Balanced Reciprocal Translocation Mosaicism (BRTM) is an extremely rare phenomenon, mainly observed in subjects with a normal phenotype accompanied by reproductive failure. To date the mechanism of origin and the incidence of BRTM are poorly defined. Here we describe 10 new cases of BRTM. In 9 cases chromosome analysis revealed the presence of two different cell lines, one with a normal karyotype and the second with an apparently balanced reciprocal translocation. In the remaining case, both cell lines showed two different, but apparently balanced, reciprocal translocations. We document the clinical implications of BRTM, discuss its frequency in our referred population and suggest that carrier individuals might be more frequent than expected.

Could a chimeric condition be responsible for unexpected genetic syndromes? The role of the single nucleotide polymorphism-array analysis

In this paper, is reported the identification of two chimeric patients, a rare finding if sexual abnormalities are absent. However, their chimeric condition is responsible at least for the Silver-Russell phenotype observed in one of the two patients. By single nucleotide polymorphism-array analyses, it was possible to clearly define the mechanism responsible for this unusual finding, underlining the importance of this technique in bringing out the perhaps submerged world of chimeras.

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.

Diploid/triploid mixoploidy: A consequence of asymmetric zygotic segregation of parental genomes

Triploidy is the presence of an extra haploid set of chromosomes and can exist in complete or mosaic form. The extra haploid set of chromosomes in triploid cells can be of maternal or paternal origin. Diploid/triploid mixoploidy is a unique form of triploid mosaicism that requires the aberrant segregation of entire parental genomes into distinct blastomere lineages (heterogoneic cell division) at the earliest zygotic divisions. Here we report on eight cases of diploid/triploid mixoploidy from our institution and conduct a comprehensive review of the literature. The parental origin of the extra set of chromosomes was determined in two cases; and, based on phenotypic evidence we propose the parental origin in the other cases. One case with complex mixoploidy appears to have a digynic origin in addition to the involvement of two different sperm. Of our eight cases, only one resulted in the birth of a live healthy child. The other pregnancies ended in miscarriage, elective termination of pregnancy, intrauterine fetal demise or neonatal death. A review of the literature and the results of our cases show that a preponderance of recognized cases of diploid/triploid mixoploidy has a digynic origin.

A case of chimerism-induced paternity confusion: what ART practitioners can do to prevent future calamity for families

In the fertility clinic setting, a negative DNA paternity test result usually suggests a sample mix-up likely occurred at the testing company or in the clinic. However, we report a case where, despite repeat negative paternity test results, the alleged father (referred to as “the proband”) was confirmed to be the baby’s father. The proband, a 34 year-old male, contacted our research group when routine blood testing revealed discrepant blood types between the parents and the baby, repeat paternity tests were negative (excluding the proband as the baby’s father), and the fertility clinic found no evidence of any wrongdoing. Microarray technology was utilized to confirm biological relatedness, which revealed an avuncular (uncle/nephew) relationship. Additional tissue samples were analyzed and family studies were conducted at paternity and forensic laboratories using STR-based DNA tests to elucidate the proband’s condition of congenital tetragametic chimerism. His paternity was subsequently affirmed and the fertility clinic exonerated of claims of a semen sample mix-up. This case underscores the possibility that some allegations of fertility clinic missteps may be explained by undiagnosed chimerism, a condition where an individual harbors two distinct genomes. We offer specific suggestions for improving laboratory reporting and creating clinical guidelines to aid in identifying and rectifying future cases of false exclusions of paternity due to chimerism.

Describing the Stem Cell Potency: The Various Methods of Functional Assessment and In silico Diagnostics

Stem cells are defined by their capabilities to self-renew and give rise to various types of differentiated cells depending on their potency. They are classified as pluripotent, multipotent, and unipotent as demonstrated through their potential to generate the variety of cell lineages. While pluripotent stem cells may give rise to all types of cells in an organism, Multipotent and Unipotent stem cells remain restricted to the particular tissue or lineages. The potency of these stem cells can be defined by using a number of functional assays along with the evaluation of various molecular markers. These molecular markers include diagnosis of transcriptional, epigenetic, and metabolic states of stem cells. Many reports are defining the particular set of different functional assays, and molecular marker used to demonstrate the developmental states and functional capacities of stem cells. The careful evaluation of all these methods could help in generating standard identifying procedures/markers for them.

Zygotes segregate entire parental genomes in distinct blastomere lineages causing cleavage-stage chimerism and mixoploidy

Dramatic genome dynamics, such as chromosome instability, contribute to the remarkable genomic heterogeneity among the blastomeres comprising a single embryo during human preimplantation development. This heterogeneity, when compatible with life, manifests as constitutional mosaicism, chimerism, and mixoploidy in live-born individuals. Chimerism and mixoploidy are defined by the presence of cell lineages with different parental genomes or different ploidy states in a single individual, respectively. Our knowledge of their mechanistic origin results from indirect observations, often when the cell lineages have been subject to rigorous selective pressure during development. Here, we applied haplarithmisis to infer the haplotypes and the copy number of parental genomes in 116 single blastomeres comprising entire preimplantation bovine embryos (n = 23) following in vitro fertilization. We not only demonstrate that chromosome instability is conserved between bovine and human cleavage embryos, but we also discovered that zygotes can spontaneously segregate entire parental genomes into different cell lineages during the first post-zygotic cleavage division. Parental genome segregation was not exclusively triggered by abnormal fertilizations leading to triploid zygotes, but also normally fertilized zygotes can spontaneously segregate entire parental genomes into different cell lineages during cleavage of the zygote. We coin the term "heterogoneic division" to indicate the events leading to noncanonical zygotic cytokinesis, segregating the parental genomes into distinct cell lineages. Persistence of those cell lines during development is a likely cause of chimerism and mixoploidy in mammals.

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.

Unusual maternal uniparental isodisomic x chromosome mosaicism with asymmetric y chromosomal rearrangement

Infertile men with azoospermia commonly have associated microdeletions in the azoospermia factor (AZF) region of the Y chromosome, sex chromosome mosaicism, or sex chromosome rearrangements. In this study, we describe an unusual 46,XX and 45,X mosaicism with a rare Y chromosome rearrangement in a phenotypically normal male patient. The patient's karyotype was 46,XX[50]/45,X[25]/46,X,der(Y)(pter→q11.222::p11.2→pter)[25]. The derivative Y chromosome had a deletion at Yq11.222 and was duplicated at Yp11.2. Two copies of the SRY gene were confirmed by fluorescence in situ hybridization analysis, and complete deletion of the AZFb and AZFc regions was shown by multiplex-PCR for microdeletion analysis. Both X chromosomes of the predominant mosaic cell line (46,XX) were isodisomic and derived from the maternal gamete, as determined by examination of short tandem repeat markers. We postulate that the derivative Y chromosome might have been generated during paternal meiosis or early embryogenesis. Also, we suggest that the very rare mosaicism of isodisomic X chromosomes might be formed during maternal meiosis II or during postzygotic division derived from the 46,X,der(Y)/ 45,X lineage because of the instability of the derivative Y chromosome. To our knowledge, this is the first confirmatory study to verify the origin of a sex chromosome mosaicism with a Y chromosome rearrangement.

Characterization of androgenetic/biparental mosaic/chimeric conceptions, including those with a molar component: morphology, p57 immnohistochemistry, molecular genotyping, and risk of persistent gestational trophoblastic disease

Recent studies have demonstrated the value of ancillary techniques, including p57 immunohistochemistry and short tandem repeat genotyping, for distinguishing hydatidiform moles (HM) from nonmolar specimens and for subtyping HMs as complete hydatidiform moles (CHM) and partial hydatidiform moles (PHM). With rare exceptions, CHMs are p57-negative and androgenetic diploid; partial hydatidiform moles are p57-positive and diandric triploid; and nonmolar specimens are p57-positive and biparental diploid. Androgenetic/biparental mosaic/chimeric conceptions can have morphologic features that overlap with HMs but are genetically distinct. This study characterizes 11 androgenetic/biparental mosaic/chimeric conceptions identified in a series of 473 products of conception specimens subjected to p57 immunohistochemistry and short tandem repeat genotyping. Fluorescence in situ hybridization was performed on 10 to assess ploidy. All cases were characterized by hydropically enlarged, variably sized and shaped villi. In 5 cases, the villi lacked trophoblastic hyperplasia, whereas in 6 there was a focal to extensive villous component with trophoblastic hyperplasia and features of CHM. The villi lacking trophoblastic hyperplasia were characterized by discordant p57 expression within individual villi (p57-positive cytotrophoblast and p57-negative stromal cells), whereas the villous components having trophoblastic hyperplasia were uniformly p57-negative in both cell types. Short tandem repeat genotyping of at least 2 villous areas in each case demonstrated an excess of paternal alleles in all regions, with variable paternal:maternal allele ratios (usually >2:1); pure androgenetic diploidy was identified in those cases with a sufficiently sized villous component having trophoblastic hyperplasia and features of CHM. Fluorescence in situ hybridization demonstrated uniform diploidy in 7 cases, including 4 of 5 tested cases with trophoblastic hyperplasia and 3 of 5 cases without trophoblastic hyperplasia. Two cases without trophoblastic hyperplasia had uniformly diploid villous stromal cells but 1 had triploid and 1 had tetraploid cytotrophoblast; 1 case with trophoblastic hyperplasia had uniformly diploid villous stromal cells but a mixture of diploid, triploid, and tetraploid cytotrophoblast. In 3 cases with a CHM component, persistent gestational trophoblastic disease developed. These results indicate that androgenetic/biparental mosaic/chimeric conceptions are most often an admixture of androgenetic diploid (p57-negative) and biparental diploid (p57-positive) cell lines but some have localized hyperdiploid components. Recognition of their distinctive p57 expression patterns and genotyping results can prevent misclassification as typical CHMs, PHMs, or nonmolar specimens. The presence of androgenetic cell lines, particularly in those with a purely androgenetic CHM component, warrants follow-up because of some risk of persistent gestational trophoblastic disease.

Clinical features of three girls with mosaic genome-wide paternal uniparental isodisomy

Here we describe three subjects with mosaic genome-wide paternal uniparental isodisomy (GWpUPD) each of whom presented initially with overgrowth, hemihyperplasia (HH), and hyperinsulinism (HI). Due to the severity of findings and the presence of additional features, SNP array testing was performed, which demonstrated mosaic GWpUPD. Comparing these individuals to 10 other live-born subjects reported in the literature, the predominant phenotype is that of pUPD11 and notable for a very high incidence of tumor development. Our subjects developed non-metastatic tumors of the adrenal gland, kidney, and/or liver. All three subjects had pancreatic hyperplasia resulting in HI. Notably, our subjects to date display minimal features of other diseases associated with paternal UPD loci. Both children who survived the neonatal period have displayed near-normal cognitive development, likely due to a favorable tissue distribution of the mosaicism. To understand the range of UPD mosaicism levels, we studied multiple tissues using SNP array analysis and detected levels of 5-95%, roughly correlating with the extent of tissue involvement. Given the rapidity of tumor growth and the difficulty distinguishing malignant and benign tumors in these GWpUPD subjects, we have utilized increased frequency of ultrasound (US) and alpha-fetoprotein (AFP) screening in the first years of life. Because of a later age of onset of additional tumors, continued tumor surveillance into adolescence may need to be considered in these rare patients.

Stem cell potency and the ability to contribute to chimeric organisms

Mouse embryonic chimeras are a well-established tool for studying cell lineage commitment and pluripotency. Experimental chimeras were successfully produced by combining two or more preimplantation embryos or by introducing into host embryo cultured pluripotent embryonic stem cells (ESCs). Chimera production using genetically modified ESCs became the method of choice for the generation of knockout or knockin mice. Although the derivation of ESCs or ESC-like cells has been reported for other species, only mouse and rat pluripotent stem cells have been shown to contribute to germline-competent chimeras, which is the defining feature of ESCs. Herein, we describe different approaches employed for the generation of embryonic chimeras, define chimera-competent cell types, and describe cases of spontaneous chimerism in humans. We also review the current state of derivation of pluripotent stem cells in several species and discuss outcomes of various chimera studies when such cells are used.

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.

Partial deletion of DMRT1 causes 46,XY ovotesticular disorder of sexual development

OBJECTIVE

Ovotesticular disorder of sexual development (DSD) is an unusual form of DSD, characterized by the coexistence of testicular and ovarian tissue in the same individual. In a subset of patients, ovotesticular DSD is caused by 46,XX/46,XY chimerism or mosaicism. To date, only a few monogenetic causes are known to be associated with XX and XY ovotesticular DSD.

DESIGN AND METHODS

Clinical, hormonal, and histopathological data, and results of high-resolution array-comparative genomic hybridization (CGH) were obtained from a female patient with 46,XY ovotesticular DSD with testicular tissue on one side and an ovary harboring germ cells on the other. Results obtained by array-CGH were confirmed by RT-quantitative PCR.

RESULTS

We detected a deletion of ∼35 kb affecting exons 3 and 4 of the DMRT1 gene in a female patient with 46,XY ovotesticular DSD. To the best of our knowledge, this is the smallest deletion affecting DMRT1 presented to this point in time.

CONCLUSIONS

We suggest that haploinsufficiency of DMRT1 is sufficient for both XY gonadal dysgenesis and XY ovotesticular DSD. Furthermore, array-CGH is a very useful tool in the molecular diagnosis of DSD.

Structural genetic variation in the context of somatic mosaicism

Somatic mosaicism is the result of postzygotic de novo mutation occurring in a portion of the cells making up an organism. Structural genetic variation is a very heterogeneous group of changes, in terms of numerous types of aberrations that are included in this category, involvement of many mechanisms behind the generation of structural variants, and because structural variation can encompass genomic regions highly variable in size. Structural variation rapidly evolved as the dominating type of changes behind human genetic diversity, and the importance of this variation in biology and medicine is continuously increasing. In this review, we combine the evidence of structural variation in the context of somatic cells. We discuss the normal and disease-related somatic structural variation. We review the recent advances in the field of monozygotic twins and other models that have been studied for somatic mutations, including other vertebrates. We also discuss chromosomal mosaicism in a few prime examples of disease genes that contributed to understanding of the importance of somatic heterogeneity. We further highlight challenges and opportunities related to this field, including methodological and practical aspects of detection of somatic mosaicism. The literature devoted to interindividual variation versus papers reporting on somatic variation suggests that the latter is understudied and underestimated. It is important to increase our awareness about somatic mosaicism, in particular, related to structural variation. We believe that further research of somatic mosaicism will prove beneficial for better understanding of common sporadic disorders.

Mouse chimeras as a system to investigate development, cell and tissue function, disease mechanisms and organ regeneration

Chimeras are organisms composed of at least two genetically distinct cell lineages originating from different zygotes. In the laboratory, mouse chimeras can be produced experimentally; various techniques allow combining different early stage mouse embryos with each other or with pluripotent stem cells. Identification of the progeny of the different lineages in chimeras permits to follow cell fate and function, enabling correlation of genotype with phenotype. Mouse chimeras have become a tool to investigate critical developmental processes, including cell specification, differentiation, patterning, and the function of specific genes. In addition, chimeras can also be generated to address biological processes in the adult, including mechanisms underlying diseases or tissue repair and regeneration. This review summarizes the different types of chimeras and how they have been generated and provides examples of how mouse chimeras offer a unique and powerful system to investigate questions pertaining to cell and tissue function in the developing and adult organism.