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Genetics/exceptions in blood types (Bombay or hh phenotype)


I am an Asian,my dad's mom and dad are cousins, my parents are cousins too. (intermarriage) Me and my brother both have O+ blood type, my dad has O+, my mom has AB+. How is this possible? I am sure this is an exception and we are NOT adopted. Can you please explain it to me and also send me reliable links or sources that can proof it? thank you very much!

Hello Refah!

You are a rare bird indeed, and this will require some explaining. Please be patient with me.

ABO blood types come from sugar molecules attached to the surfaces of your blood cells. The immune system uses sugar encoding on cell surfaces to recognize if the cell is part of you or not. Immune cells do this by binding (grabbing onto) 3D structures that do not match the cell memory of self. In a blood transfusion the immune system would immediately notice a flood of new cells! However, if those cells are wearing not-self sugars (rather like the opposing team's sport uniform) the immune system would assume a massive infection and attack all the new cells, killing them. This also tends to kill the transfusion recipient. If your ABO blood type matches, you have the same 'sugar uniform' on your red blood cells as the donated blood, so your immune system doesn't react... much to your relief in an emergency.

A more technical explanation of ABO blood groups may be found here:
(This is the American National Center for Biotechnology Information, or NCBI. It is funded by the US government and tends to be accurate in the sense that it matches up with the most current knowledge.)

What is interesting is that the ABO types come from different versions of one gene and one protein. This protein's function is to attach extra sugars on the red blood cell surface for immune system recognition. (Called a glycosyltransferase in science speak.) Why? We are unsure, but we know it happens.

If you have the A type protein, you get one sugar added called N-acetyl glucosamine. If you have B, you get fucose. AB has inherited the A type on one parental chromosome and the B type on the other, so their red blood cells come decorated with both sugars.

O type means 'null' - the enzyme does not stick any extra sugar on your red blood cells.

An O-type person getting AB cells would have an immune reaction to the 'alien' cells, rendering the blood transfusion useless and the patient dead.  However, an AB person's immune system would not notice 'missing' sugars on O-type blood. (The immune system is lazy and does not react to missing things, fortunately; otherwise it would think we are sick all the time!)

Why am I going to all this trouble explaining this to you?

There is a wrinkle in this system; there is a building block 'flagpole' of sugars in the red blood cell immune cell recognition structure called 'H'. If your H is broken, you have no intermediate sugar flagpole upon which to hang the final ABO sugar 'flag'. The ABO glycosyltransferase works, but it cannot find its partner to modify, so nothing happens. Since you get one H gene from each parent, a single chromosome copy of a working H will compensate for a broken one, and everything may appear normal when it comes to blood type. An Hh person appears to follow the classic dominant/recessive Mendelian gene pattern of ABO inheritance just fine.

However, if both copies of the H flagpole assembly gene are broken,  a patient will present as 'O' clinically regardless of which ABO group a genetic test would indicate he or she should possess .  This means an hh patient has an immune system that prefers naked red blood cells to ones wearing what it perceives as 'enemy' sugars, so cannot receive blood donations from anyone who is not hh.

In your case, it is likely your mother is Hh; she has the gene to build flagpoles so she can still fly AB flags. Your mother has a 50% chance of passing on the 'no flagpole at all' phenotype to her children, regardless of what ABO group she may also pass on at the same time.  We do not know if your father is Hh with O 'flags' or hh with any 'flags' unless a test is done for the presence of the H flagpole itself. We do know that if you or your brother inherited a working H, you would have either an A or B blood type, so you both have hh blood.

What does this mean for you? It is very likely that should you need a blood transfusion you would need it from yourself (stored blood) or your brother.  A blood bank technician can perform the agglutination test to see if transfusions are possible from your father or not, but there are no guarantees; if he is Hh OO then a transfusion from him will kill you. Luckily, other than the problems getting a blood transfusion (drive safely!) there are no other documented health issues resulting from the hh phenotype to trouble you. You might consider registering with your local blood bank as a rare donor; with your blood type anyone can be a recipient, even other hh folks.

NCBI talking about hh inheritance:

There are a few populations in the world that are known to have a broken H protein; this is often referred to as hh or 'the Bombay phenotype'. (Wikipedia on Bombay: There is anecdotal information on the Web that Bombay phenotypes are found most often in families with a history of cosanguinity. (intermarriage) This would make sense given the genetic inheritance pattern and the rarity of the condition, though spontaneous mutations can and do occur.

Cheers! Let me know if you have further questions.


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Trista Robichaud, PhD


No homework questions, especially ones copied and pasted from textbooks. I will answer questions about principles or give hints, but I do not do other's homework. I'm comfortable answering basic biochemistry, chemistry, genetics, and biology questions up to and including an undergraduate level of understanding. This includes molecular biology, protein purification, and genetics. My training/inclination is primarily in structural biology, or how the shapes of things affect their function. Other interests include protein design, protein engineering, enzyme kinetics, and metabolic diseases such as cancer, atherosclerosis, and diabetes. Regrettably, I cannot diagnose any disease. I can tell you how we currently understand the basic science behind a disease state, but I cannot recommend treatment in any way. Please direct such questions to your medical professional.


I hold a PhD in Biomedical Science from the University of Massachusetts Medical School in Worcester. I specialize in Biochemistry, with a focus on protein chemistry. My thesis work involved the structure and functions of the human glucose transporter 1. (hGLUT1) Currently I am a postdoc working in peptide (mini-protein) design and enzymology at the University of Texas Health Science Center in San Antonio, Texas. I am in Bjorn Steffensen's lab, researching inhibitors of gelatinase A, a matrix metalloproteinase. I have also been answering Chemistry/Biochemistry questions on this site since summer 2010.

2001 American Association for the Advancement of Science, 2007 American Chemical Society 2007 Protein Society 2011 UTHSCSA Women’s Faculty Association

Publications Levine KB, Robichaud TK, Hamill S, Sultzman LA, Carruthers A. Properties of the human erythrocyte glucose transport protein are determined by cellular context. Biochemistry 44(15):5606-16, 2005. (PMID 15823019) Robichaud TK, Appleyard AN, Herbert RB, Henderson PJ, Carruthers A “Determinants of ligand binding affinity and cooperativity at the GLUT1 endofacial site” Biochemistry 50(15):3137-48, 2011. (PMID 21384913) Xu X, Mikhailova M, Chen Z, Pal S, Robichaud TK, Lafer EM, Baber S, Steffensen B. “Peptide from the C-terminal domain of tissue inhibitor of matrix metalloproteinases-2 (TIMP-2) inhibits membrane activation of matrix metalloproteinase-2 (MMP-2)” Matrix Biol. 2011 Sep;30(7-8):404-12. (PMID: 21839835) Robichaud TK, Steffensen B, Fields GB. Exosite interactions impact matrix metalloproteinase collagen specificities. J Biol Chem. 2011 Oct 28;286(43):37535-42 (PMID: 21896477) Poster Abstracts: Robichaud TK, Carruthers. A Mutagenesis of the Human type 1 glucose transporter exit site: A functional study. ACS 234th Meeting, Boston MA. Division of Biological Chemistry, 2007 Robichaud TK, Bhowmick M, Tokmina-Roszyk D, Fields GB “Synthesis and Analysis of MT1-MMP Peptide Inhibitors” Biological Chemistry Division of the Protein Society Meeting, San Diego CA 2010 Robichaud TK; Tokmina-Roszyk D; Steffensen B and Fields GB “Exosite Interactions Determine Matrix Metalloproteinase Specificities” Gordon Research Conference on Matrix Metalloproteinase Biology, Bristol RI 2011

INSTITUTION AND LOCATION DEGREE (if applicable) YEAR(s) FIELD OF STUDY Oakland University, Auburn Hills MI BS 1993-1998 Biochemistry University of Massachusetts Medical School, Worcester MA PhD 2001-2008 Biochemistry & Molecular Pharmacology University of Texas Health Science Center, San Antonio TX Postdoc 2009-Present Biochemistry

Awards and Honors
1998 Honors College Graduate, Oakland University 2009 Institutional National Research Service Award, Pathobiology of Occlusive Vascular Disease T32 HL07446 2011 1st Place, Best Postdoctoral Poster, Dental Science Symposium, UTHSCSA, April 2011

Past/Present Clients
Invited Seminars: Robichaud TK, Fields GB. “Synthesis and Analysis of MTI-MMP Triple Helical Peptide Inhibitors” Pathology Research Conference, University of Texas Health Science Center San Antonio Pathology Department (June 18th, 2010) Robichaud TK & Hill, B “How To Give A Great Scientific Talk” Invited Lecture, Pathobiology of Occlusive Vascular Disease Seminars, UTHSCSA (Nov 11th 2010), Cardiology Seminar Series, Texas Research Park (Feb 21st, 2011) Robichaud TK; Tokmina-Roszyk D; Steffensen B and Fields GB “Exosite Interactions Determine Matrix Metalloproteinase Specificities” Gordon-Keenan Research Seminar “Everything You Wanted to Know About Matrix Metalloproteinases But Were Afraid to Ask” Bristol, RI (Aug 6th, 2011)

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