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Monday, April 15, 2013

Yet another blood group

Blood typing (determining what kinds of antigens a person has on the surface of his or her red blood cells) is a series business. Giving a person the wrong type of blood can have dire consequences. Unfortunately, blood typing is also complicated by the fact that there are so many different classes of antigens to consider (for more background, see my post on the discovery of two new blood groups). Just when you think you’ve covered all your bases, someone succumbs to an acute hemolytic transfusion reaction because of a previously unidentified red blood cell antigen.

One such unhappy event happened in 1952 when a patient referred to as ‘Mrs. Vel’ nearly died after receiving what her doctors thought was a perfectly compatible blood transfusion. It turns out that Mrs. Vel was missing an antigen (later called the Vel antigen) present in the donated blood. This discrepancy resulted in the widespread destruction of her red blood cells.

In an effort to avoid repeating this error, researchers screened tens of thousands of donated blood samples to see which, if any, would not cross react with Mrs. Vel’s blood. The scientists found that only about one person in two thousand was missing the Vel antigen. This effectively means that people like Mrs. Vel are probably out of luck if they need a blood transfusion. More importantly, it means that it’s critical to identify Vel minus people before giving them blood of any kind.

Needless to say, finding the Vel gene would make the screening process much easier. Now, many of the same researchers who brought you the Langereis and Junior blood groups have done just that. The scientists discovered that a gene known as SMIM1 was responsible for encoding the Vel antigen. Vel minus people are missing seventeen nucleotides from their copies of this gene, effectively nullifying the protein as a surface antigen.

This should make it much easier to rapidly identify Vel minus people before they receive life-threatening blood transfusions. It also brings the number of blood typing groups up to 33. Luckily, blood typing tends to be automated these days, so most people have no need to remember all 33 factors. Personally, I only know my blood type for two blood systems: ABO and rhesus. Statistically speaking, I’m probably Vel plus, and I have no idea for the other thirty groups.

Ballif BA, Helias V, Peyrard T, Menanteau C, Saison C, Lucien N, Bourgouin S, Le Gall M, Cartron JP, & Arnaud L (2013). Disruption of SMIM1 causes the Vel- blood type. EMBO molecular medicine PMID: 23505126.