Blood Chimerism in Dizygotic Monochorionic Twins During 5 Years Observation

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.

Laboratory Monitoring of Mother, Fetus, and Newborn in Hemolytic Disease of Fetus and Newborn

Background

Laboratory monitoring of mother, fetus, and newborn in hemolytic disease of fetus and newborn (HDFN) aims to guide clinicians and the immunized women to focus on the most serious problems of alloimmunization and thus minimize the consequences of HDFN in general and of anti-D in particular. Here, we present the current approach of laboratory screening and testing for prevention and monitoring of HDFN at the Copenhagen University Hospital in Denmark.

Summary

All pregnant women are typed and screened in the 1st trimester. This serves to identify the RhD-negative pregnant women who at gestational age (GA) of 25 weeks are offered a second screen test and a non-invasive fetal RhD prediction. At GA 29 weeks, and again after delivery, non-immunized RhD-negative women carrying an RhD-positive fetus are offered Rh immunoglobulin. If the 1st trimester screen reveals an alloantibody, antenatal investigation is initiated. This also includes RhD-positive women with alloantibodies. Specificity and titer are determined, the fetal phenotype is predicted by non-invasive genotyping based on cell-free DNA (RhD, K, Rhc, RhC, RhE, ABO), and serial monitoring of titer commences. Based on titers and specificity, monitoring with serial peak systolic velocity measurements in the fetal middle cerebral artery to detect anemia will take place. Intrauterine transfusion is given when fetal anemia is suspected. Monitoring of the newborn by titer and survival of fetal red blood cells by flow cytometry will help predict the length of the recovery of the newborn.

Prenatal prediction of fetal Rh C, c and E status by amplification of maternal cfDNA and deep sequencing

BACKGROUND

The Rh blood group system has considerable clinical importance. The C, c, and E antigens are targets of alloantibodies. Anti-C, anti-c or anti-E alloreactive antibodies produced in pregnant women can cause anemia of a fetus carrying the corresponding antigens.

AIMS

Based on NGS technology, we have developed a noninvasive diagnostic assay to predict the fetal blood group of C, c or E antigens by sequencing cell-free DNA (cfDNA) during pregnancy.

MATERIALS AND METHODS

The SNVs underlying either the C, c or E antigens were PCR amplified and sequenced using NGS on a MiSeq instrument. The DNA sequences encoding the C, c or E antigen were counted, as were the number of total sequences. Based on the percentage of fetally derived target SNVs inherited from the father, the fetal blood group could be predicted.

RESULTS

The results of 55 consecutive RHCE prenatal analyses with postnatal serological blood group determination of 30 newborns showed no discordant results. A threshold discerning positive from negative samples was set at 0.05% specific reads.

DISCUSSION

Noninvasive, prenatal prediction of fetal blood groups by sequencing cfDNA for the detection of low-level RHCE*C, RHCE*c and RHCE*E sequences was established as an accurate and robust assay applicable for use in clinical settings.

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.

Interspecies chimeras

By probing early embryogenesis and regeneration, interspecies chimeras provide a unique platform for discovery and clinical use. Although efficient generation of human:animal chimeric embryos remains elusive, recent advancements attempt to overcome incompatibilities in xenogeneic development and transplantation.