Cis AB

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Cis AB is a rare mutation in ABO gene which complicates the basic inheritance pattern and blood-transfusion compatibility matching for ABO blood typing. There are different DNA mutations either type A or Type B alleles that changes several amino acids in enzyme transferase A or B, homologous enzymes differing in only four of 354 amino acids (R176G, G235S, L266M, and G268A). A single change in ABO gene dna could reverse type B to type A and then, new hybrid enzyme B will produce a bit of A antigene (in serum test, A2B). The most common is a A102 allele variation in exon 7 nucleotide position G803C changing Glycine (type A) by Alanine (type B) . They are expressed both like an standard (trans) AB type but is totally different. AB type gets A and B antigenes from father and mother while cis-AB allele comes from one parent only. In serum test, cis-AB is almost the same as AB, but people with this rare type have got problems about blood infusion. Some of them need components like washed red blood cells or autotransfusion serum and blood. Cis-AB type was studied first in Japan (Shishoku Island) and South Korea (Gwanju area) where this rare type is more common (Chinese coast provinces and Taiwan, too), although in a few European families (France, Spain, Belgium, Germany, Poland) is present, too. In the year 2004, American Red Cross described a family in Nebraska with a father type cis-AB rh negative, a mother type O and their baby type cis-AB. Since that, several cases in America have been reported. In Cis AB inheritance, A and B antigenes can live together in the same allele. These can happen due to mutant alleles at ABO locus (multiple variants are available). Usually it is a single allele making a single enzyme which can make both A and B antigens.[1] Antigen expression is weaker than A1 or B.

Scenarios[edit]

When one parent carries a Cis AB allele, the other allele can be any of O, A or B and the phenotype of this parent is anyway AB, but the children will inherit either the AB or the other allele from this parent.

  1. If the other parent is O phenotype (OO genotype) there can be three likely scenarios for blood group of children of a Cis AB carrier (and a 4th very unlikely scenario):
    1. The second allele is O: children are either AB or O
    2. Second allele is A: Children are either AB or A
    3. Second allele is B: Children are either AB or B
    4. A very rare 4th possibility exists: if the other allele is also Cis AB then the children will be always AB irrespective whatever the other parent is, because they will have one cis AB allele from this parent.
  2. If the other parent is A, depending on whether this parent is genotypically AA or AO and what the other allele is in the Cis Ab carrying parent, there are following possible scenarios:
    1. Other parent is AO and second allele is O: The children are either AB or A or O
    2. Other parent is AA and the second allele is O: The children are either AB or A
    3. Other parent is AO and second allele is A: The children are either AB or A
    4. Other parent is AA and the second allele is A: The children are either AB or A
    5. Other parent is AO and the second allele is B: The children are either AB or B
    6. Other parent is AA and the second allele is B: The children are always AB
    7. Rare situation: If the other allele is also cis AB:The children are always AB
  3. Like wise there will be similar scenarios for the other parent being B:
    1. Other parent is BO and second allele is O: The children are either AB or B or O
    2. Other parent is BO and second allele is A: The children are either AB or A
    3. Other parent is BO and the second allele is B: The children are always AB or B
    4. Other parent is BB and the second allele is B: The children are either AB or B
    5. Other parent is BB and the second allele is O: The children are either AB or B
    6. Other parent is BB and the second allele is A: The children are always AB
    7. Rare situation: If the other allele is also cis AB:The children are always AB

(Caution: ABO inheritance is generally derived assuming the children are not the very rare Bombay phenotype which would require both parents to be carriers of it.)

Real life implications[edit]

Maternity and paternity disputes[edit]

There can be paternity or maternity disputes if tested by ABO blood grouping. Those of the above scenarios where a child's phenotype is written in bold will be such a situation. For example (scenario 1.1 above) a child of a cis AB (who will apparently look as a regular AB phenotype) individual and an O individual will be either AB or O instead of the usual A or B (see diagram above).

Differential diagnosis[edit]

If the child of an AB and an O individual is O (the green colored offspring in the scenario 1 image above), then a rare alternative possibility is that the parents were carriers (heterozygous) for the Bombay phenotype (Hh) and the child is a Bombay (hh) homozygous by genotype thus expressing Bombay phenotype also called Oh where irrespective of the presence of the ABO alleles the substrate from which those antigens are made is not made and thus A, B and even O antigen is completely absent.

References[edit]

  1. ^ Mark H. Yazer, Martin L. Olsson, Monica M. Palcic, The cis-AB Blood Group Phenotype: Fundamental Lessons in Glycobiology, Transfusion Medicine Reviews, Volume 20, Issue 3, July 2006, Pages 207-217, ISSN 0887-7963, doi:10.1016/j.tmrv.2006.03.002. (http://www.sciencedirect.com/science/article/B75B5-4K6R7W1-8/2/31e62338a662627d515cd7d647cba531) doi:10.1016/j.physletb.2003.10.071

Transfusion. 2002 Feb;42(2):239-46. A novel cis AB allele derived from a B allele through a single point mutation. Roubinet F1, Janvier D, Blancher A.

Rev Fr Transfus Immunohematol. 1975 Mar;18(1):11-25. [The Cis AB complex of the ABO system]. [Article in French] Salmon C, Lopez M, Liberge G, Gerbal A.

Genetic mechanism of cis-AB inheritance. I. A case associated with unequal chromosomal crossing over.A Yoshida, H Yamaguchi, and Y Okubo

Ann. Hum. Genet. (2002), 66, 1±27 ' University College London DOI: 10.1017}S0003480001008995 Printed in the United Kingdom 1 Sequence variation at the human ABO locus S. P. YIP Department of Nursing and Health Sciences, The Hong Kong Polytechnic University, China

Vox Sang. 1993;64(2):120-3. Molecular genetic analysis of the ABO blood group system: 2. cis-AB alleles. Yamamoto F1, McNeill PD, Kominato Y, Yamamoto M, Hakomori S, Ishimoto S, Nishida S, Shima M, Fujimura Y.

Vox Sang. 2004 Jul;87(1):41-3. The serological and genetic basis of the cis-AB blood group in Korea. Cho D1, Kim SH, Jeon MJ, Choi KL, Kee SJ, Shin MG, Shin JH, Suh SP, Yazer MH, Ryang DW.