Para-Bombay: A blind spot in blood grouping?

Incidental Discovery of a Patient with the Bombay Phenotype

Bombay phenotype, an exceptionally rare blood type in individuals outside of Southeast Asia, occurs in approximately 1 in 1,000,000 individuals in Europe. This blood phenotype is characterized by the absence of the H antigen on red blood cells (RBCs) and in secretions. As the H antigen is the structure on which the ABO system is built, individuals lacking this antigen are unable to produce A or B antigens and appear as type O on routine ABO phenotyping. H deficiency does not cause ill effect; however, these individuals produce an anti-H alloantibody capable of causing severe acute hemolytic transfusion reactions when exposed to RBCs that express the H antigen. In this case study, we highlight the incidental discovery of a patient with Bombay phenotype in a North American hospital system, expected test results, the immunologic and genetic basis underlying the Bombay and para-Bombay phenotypes, and methods to ensure availability of compatible blood.

Two novel alleles on Fucosyltransferase 2 from northern Thai para-Bombay family and computational prediction on mutation effect

BACKGROUND

Major characteristics of the para-Bombay phenotype are the absence of ABH antigens on red blood cells due to fucosyltransferase 1 (FUT1) gene mutation and the presence of these antigens in body secretions due to the active fucosyltransferase 2 (FUT2) gene. An ABO blood group discrepancy can be identified via serological testing, and additional tests can be performed for confirmation. This study aimed to resolve the ABO discrepancy and report two novel alleles on the FUT2 gene in northern Thai para-Bombay families.

STUDY DESIGN AND METHODS

Twelve blood samples were collected from five suspected para-Bombay donors and their families. Nucleotide sequences of ABO, FUT1, and FUT2 were analyzed by polymerase chain reaction-sequence-based typing. Bioinformatics tools were used to predict the effect of suspected novel FUT2 alleles.

RESULTS

All samples exhibited normal ABO alleles, concordant with serological test results. FUT1 exhibited three known variants (c.328G>A, c.424C>T, and c.658C>T). Although FUT2 exhibited two known variants (c.357C>T and c.385A>T), two novel alleles were observed. One allele consisted of c.98A>G, c.101T>G, and c.357C>T with predicted normal transferase activity, whereas the other consisted of c.357C>T and c.617T>C with predicted abnormal enzyme activity.

DISCUSSION

Two novel alleles in FUT2 were reported among the affected para-Bombay individuals of northern Thai families. The c.617T>C variant caused an amino acid change from valine to alanine at position 206, predicted to be an inactive FUT2 enzyme. Inheritance of this variant with the recessive FUT1 allele may lead to inheritance of the rare Bombay blood group in the progeny.

Transfusion practice blind spot in para-Bombay: A case report

H-deficient phenotype individuals with absent or weak anti-H activity may remain undetected on standard routine blood grouping. We report a case of a 59-year-old-man presented with symptomatic anaemia secondary to upper gastrointestinal bleed with haemoglobin level of 68 g/L who required two units of packed red blood cells. He was previously grouped as O Rh D positive and had a history of uneventful multiple blood transfusions. His latest pre-transfusion investigations showed ABO discrepancy between forward and reverse blood grouping, pan-agglutination in both antibody screening and identification with negative direct Coombs test and autocontrol. Further testing including anti-H lectin test and saliva secretor study confirmed that the patient blood group was para-Bombay B RhD positive. This case highlights that the para-Bombay phenotype can be mistakenly labelled as "O" if further investigations are not performed.

ABO phenotype-protected reproduction based on human specific α1,2 L-fucosylation as explained by the Bombay type formation

The metabolic relationship between the formation of the ABO(H) blood group phenotype and human fertility is evident in the case of the (Oh) or Bombay blood type, which Charles Darwin would have interpreted as resulting from reduced male fertility in consanguinities, based on the history of his own family, the Darwin/Wedgwood Dynasty. The classic Bombay type occurs with the extremely rare, human-specific genotype (h/h; se/se), which (due to point mutations) does not encode fucosyltransferases 1(FUT1) and 2 (FUT2). These enzymes are the basis for ABO(H) phenotype formation on the cell surfaces and fucosylation of plasma proteins, involving neonatal immunoglobulin M (IgM). In the normal human blood group O(H), which is not protected by clonal selection with regard to environmental A/B immunization, the plasma contains a mixture of non-immune and adaptive anti-A/B reactive isoagglutinins, which in the O(h) Bombay type show extremely elevated levels, associated with decreased levels of fucosylation-dependent functional plasma proteins, suchs as the van Willebrand factor (vWF) and clotting factor VIII. In fact, while the involvement of adaptive immunoglobulins remains unknown, poor fucosylation may explain the polyreactivity in the Bombay type plasma, which exhibits pronounced complement-binding cross-reactive anti-A/Tn and anti-B IgM levels, with additional anti-H reactivity, acting over a wide range of temperatures, with an amplitude at 37 °C. This aggressive anti-glycan-reactive IgM molecule suggests the induction of ADCC (antibody-dependent) and/or complement-mediated cytotoxicity via overexpressed glycosidic bond sites against the embryogenic stem cell-to-germ cell transformation, which is characterized by fleeting appearances of A-like, developmental trans-species GalNAcα1-O-Ser/Thr-R glycan, also referred to as the Tn (T "nouvelle") antigen.

A case of nearly mistaken AB para-Bombay blood group donor transplanted to a group 'O' recipient

Unintentional ABO mismatch kidney transplantation can cause detrimental hyperacute rejection. We report the first successful ABO incompatible kidney transplantation from an AB para-Bombay donor to O recipient. At the initial evaluation, the donor's ABO type was discordance on the cell typing and serum typing, which typed to be 'O' as cell typing and 'AB' as serum typing. At the second investigation, it was confirmed that the donor had a unique, rare but not uncommon blood type AB para-Bombay which was incompatible with the recipient's blood group. The kidney transplantation was successfully performed by an ABO incompatible preconditioning, double filtration plasmapheresis (DFPP) and rituximab. The serum creatinine at 12 months post-transplantation was 1.3 mg/dL. The pathology of the kidney biopsy showed no signs of rejection.