[Identification of a pregnant woman with tetragametic chimera of 46,XY/46,XX karyotype presenting as mixed agglutination during ABO blood group forward typing].

چکیده اصلی

OBJECTIVE: To conduct blood group identification and genetic analysis on a pregnant woman suspected for having ABO blood group chimerism, and to explore the blood group identification methods and formation mechanisms of her chimerism. METHODS: A pregnant woman with mixed-field (MF) agglutination reactions in ABO forward typing detected at the Department of Transfusion, Zhongshan Hospital, Xiamen University on May 10, 2025 was selected as study subject. Blood grouping was carried out using a microcolumn gel method and saline method. The two populations of red blood cells (RBCs) from the proband, including those agglutinated and non-agglutinated with anti-A reagent, were separated for repeated blood grouping. Flow cytometry was used to quantitatively analyze the proportion of the two RBC populations. ABO genotyping was conducted via direct sequencing and PacBio long-read single-molecule real-time (SMRT) sequencing. Short tandem repeat (STR) analysis was performed on the proband's blood, buccal swabs, hair follicle samples, and the blood samples of her parents. Genetic analysis was carried out using multiplex PCR testing for Y-chromosome microdeletions, chromosomal karyotyping, and fluorescence in situ hybridization (FISH). This study was approved by the Medical Ethics Committee of the hospital (Ethics No.: xmzsyyky 2025-070). RESULTS: The proband's RBCs showed 4+ MF agglutination with anti-A, anti-A1, and anti-AB antibodies. After separation, agglutinated RBCs presented the A1 phenotype and non-agglutinated RBCs presented the O phenotype. Phenotyping for 14 additional RBC antigens showed no MF reaction. Flow cytometry showed that A-phenotype RBCs have accounted for 31.6%, and O-phenotype RBCs have accounted for 69.4%. Direct sequencing of the ABO gene revealed that the proband had an A1.02/O.01.01 genotype. SMRT sequencing results confirmed the presence of three distinct ABO allelic haplotypes: O.01.01 (containing the IVS4+102C>A variant), O.01.01, and A1.02. STR analysis showed that the TH01 and Penta E loci in the proband's multiple tissue samples all exhibited dual paternal and maternal DNA contributions, and a characteristic Y-chromosome peak was detected at the AMEL locus. Multiplex PCR for Y-chromosome microdeletions confirmed that the proband carried the AZFa/b/c, SRY and ZFY genes. G-banded karyotype analysis showed that the proband has a karyotype of 46,XY[1]/46,XX[99]. FISH revealed that the proportion of XY-karyotype cells in cultured peripheral blood was significantly lower than uncultured specimens. CONCLUSION: The proband is an ABO blood group chimera and a tetragametic chimera with a 46,XY/46,XX karyotype distributed throughout the body. This chimerism has originated from the fusion of male and female dizygotic twin embryos during early development.

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