A dispermic chimera with mixed field blood group B and mosaic 46,XY/47,XYY karyotype

A prenatal case misunderstood as specimen confusion: 46,XY/46,XY chimerism

Chimerism results from the fusion of two zygotes in a single embryo, whereas mosaicism results from mitotic errors in a single zygote. True human chimerism is rare, with fewer than 100 cases reported in the literature. Here, we report a case in which the fetus was identified as having tetragametic chimerism based on short tandem repeat - polymerase chain reaction analysis of the family observed during amniocentesis for advanced maternal age. The chimerism occurred via the fertilization of two ova by two spermatozoa, followed by the fusion of early embryos. The genotypes of the two amniotic fluid samples obtained successively by one puncture were completely different, and the sex chromosomes were XY. Karyotyping and copy number variation sequencing showed no abnormalities. The fetus was delivered at term and the phenotype of the newborn was normal.

Application of Blood Group Genotyping by Next-Generation Sequencing in Various Immunohaematology Cases

BACKGROUND

Next-generation sequencing (NGS) technology has been recently introduced into blood group genotyping; however, there are few studies using NGS-based blood group genotyping in real-world clinical settings. In this study, we applied NGS-based blood group genotyping into various immunohaematology cases encountered in routine clinical practice.

METHODS

This study included 4 immunohaematology cases: ABO subgroup, ABO chimerism, antibody to a high-frequency antigen (HFA), and anti-CD47 interference. We designed a hybridization capture-based NGS panel targeting 39 blood group-related genes and applied it to the 4 cases.

RESULTS

NGS analysis revealed a novel intronic variant (NM_020469.3:c.29-10T>G) in a patient with an Ael phenotype and detected a small fraction of ABO*A1.02 (approximately 3-6%) coexisting with the major genotype ABO*B.01/O.01.02 in dizygotic twins. In addition, NGS analysis found a homozygous stop-gain variant (NM_004827.3:c.376C>T, p.Gln126*; ABCG2*01N.01) in a patient with an antibody to an HFA; consequently, this patient's phenotype was predicted as Jr(a-). Lastly, blood group phenotypes predicted by NGS were concordant with those determined by serology in 2 patients treated with anti-CD47 drugs.

CONCLUSION

NGS-based blood group genotyping can be used for identifying ABO subgroup alleles, low levels of blood group chimerism, and antibodies to HFAs. Furthermore, it can be applied to extended blood group antigen matching for patients treated with anti-CD47 drugs.

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.

The first case of congenital blood chimerism in two of the triplets in Korea

BACKGROUND

Chimeras are composed of two or more different populations that originated from different zygotes. Blood chimerism arising from twins have been reported in the literature. Herein, we report the first blood group chimerism in triplets.

METHODS

ABO blood grouping was carried out by manual tile methods (Merck Millipore, UK) and micro-column agglutination method (Bio-Rad, Cressier sur Morat, Switzerland). Flow cytometric analysis was performed with Anti-A-PE conjugated monoclonal antibodies (BD Biosciences, San Jose, CA, USA) and FACS Canto II (BD Biosciences). Molecular analysis was performed with allele-specific polymerase chain reaction (AS-PCR) and direct sequencing of the exons 6 and 7.

RESULTS

Mixed-field agglutination and weak agglutination against anti-A were revealed by ABO blood grouping. Flow cytometric analysis revealed the presence of both A cells and O cells. AS-PCR and sequencing showed two neonates with chimerism, with each neonate`s genotype being A102/O01/O02.

CONCLUSION

This is the first recorded case of blood chimera from a triplet in Korea. We recommend full investigation of blood group chimerism in neonates with ABO discrepancy, as blood chimerism is subject to certain caution in the clinical environment.

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.

A 45,X/46,XY DSD (Disorder of Sexual Development) case with an extremely uneven distribution of 46,XY cells between lymphocytes and gonads

In 45,X/46,XY DSDs, the proportion of the two cell lineages is uneven in different organs and tissues, and 45,X and 46,XY cells can be found throughout the body. The gonadal development of 45,X/46,XY patients depends on the population of 46,XY cells in the gonads and the clinical features are variable. We had a 45,X/46,XY DSD patient whose 46,XY population in peripheral blood was extremely low, less than 0.2%, and was not detected by FISH analysis. However, the patient showed bilateral testicular development and more than 50% of the cells in the gonads had the 46,XY karyotype. This case suggests that a drastically imbalanced distribution could occur in 45,X/46,XY DSD cases.

Amplification refractory mutation system-PCR is essential for the detection of chimaeras with a minor allele population: a case report

Blood chimaera is a rare but important issue for immunohaematology laboratories. Several molecular approaches, such as ABO genotyping, human leucocyte antigen (HLA) typing and DNA short tandem repeat (STR) analysis, have been used to identify chimaerism. Unfortunately, the minor allele population can be overlooked by PCR-based methods, which preferentially amplify the major allele population. A case with AweakB (AwB), demonstrating a mixed-field pattern, was sent to our laboratory for further evaluation. Direct sequencing of ABO exons 6 and 7 revealed a B101/O02 genotype. Analysis of the 12 STR loci and HLA typing did not provide any evidence of chimaerism. However, amplification refractory mutation system (ARMS)-PCR identified the minor A102 allele in addition to B101/O02. Three alleles of the chimaera were confirmed by cloning and sequencing. Thus, ARMS-PCR is essential, especially in the case of a chimaera with a minor allele population.