Not long after Karl Landsteiner first described the different ABO blood types, scientists started looking for associations between blood type and other human traits.  Some of their theories were truly weird (more on these tomorrow!), but some have held up to scientific scrutiny.

Venous Thromboembolism (VTE)
People with non-type O blood (A, B and AB) have been shown to be at increased risk for VTE.  The reason is thought to be that these people have higher levels of the clot-inducing proteins factor VIII and von Willebrand factor in their blood.  Having non-type O blood further raises the already increased risk for VTE in people who carry the Factor V Leiden and prothrombin G20210A mutations.

Cancer
Since the 1950s, scientists have found that people with type O blood have decreased risk for stomach cancer compared to people with type A.  Other cancers (pancreatic, breast, ovarian, cervical) also occur at lower rates in people with type O blood.  No one is quite sure why this is.  It could be that the sugars found on type A blood cells, which are also expressed by other cells in the body, might somehow help cancers grow more aggressively.  Alternatively, some research has shown that regardless of person’s own blood type, tumors express the type A sugars. In people with type A blood, these sugars go unnoticed by the immune system because they are considered normal.  But in people with type O blood, these new sugars are recognized as foreign, spurring the immune system to destroy the tumors.

Stomach Ulcers
Although stomach cancer is less prevalent in people with type O blood, stomach ulcers are more common in people with this blood type.  The sugars that define the different blood types are also found on cells in the gastrointestinal tract.  Research has shown that these sugars influence the ability of H. pylori, a type of bacteria responsible for a large number of stomach ulcers, to attach to the lining of the stomach.  People with type A or B blood (and hence A or B sugars on their stomach cells) have fewer H. pylori receptors than people with type O.

Severe Malaria
In people infected with malaria, more severe disease is seen in those whose red blood cells are induced to form rosettes, large aggregates that block small blood vessels.  Studies have shown that people with type O blood form fewer, smaller and more easily broken up rosettes than people with type A, B or AB blood.  This is probably because the sugars found on the non-O blood cells end up helping to create larger clumps of cells.

Infectious Disease
Some studies have shown that certain bacterial and viral infections are more or less likely in certain blood types.  For example, type A blood has been linked to a predisposition to “glue ear,” which is caused by infection with Pseudomonas aeruginosa. And some studies suggest that people with type O or B blood are less susceptible to smallpox. The research supporting these and other claims of an impact of blood type on infectious diseases are not as strong as the other associations listed above, however.

(23andMe customers can get a prediction of their ABO blood type based on their DNA data through the new ABO Lab feature.)

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This Monday acting Surgeon General Steven K. Galson issued a Call to Action to reduce the number of people in the United States affected by two serious blood clotting conditions: deep vein thrombosis and pulmonary embolism.

Deep vein thrombosis (DVT), sometimes called “economy class syndrome” is the formation of a blood clot in a vein deep within the body, usually in the legs. Pulmonary embolism (PE) occurs if the clot breaks free and travels through the circulatory system to the lungs. Together these two conditions affect an estimated 350,000 to 600,000 Americans each year and contribute to at least 100,000 deaths.

“Deep vein thrombosis and pulmonary embolisms are often ’silent’ conditions — they can occur suddenly and without symptoms,” Galson said in a statement. “But we have made a lot of progress in understanding how these disorders develop and how to prevent, diagnose, and treat them. It’s time to put this knowledge into action.”

Researchers have found that DVT and PE usually develop in response to a triggering event – being hospitalized or confined to bed rest, having major surgery, suffering a trauma, or traveling for several hours — in people who either have an inherited predisposition to blood clotting disorders or another risk factor.

23andMe customers have access to their data for the two most common genetic risk factors for DVT and PE (collectively known as Venous Thromboembolism).

Having the riskier version of one or both of the SNPs 23andMe reports data for (Factor V Leiden and Prothrombin 20210) significantly increases the risk of developing DVT or PE. An estimated 15 to 20 percent of DVT/PE patients have the Factor V Leiden mutation, while 6 percent have the Prothrombin 20210 mutation.

The average risk of DVT/PE in people between the ages of 40 and 59 (anyone can be afflicted, but risk does increase with age) is 2.5%. But in those people in this age group who inherit a copy of the Factor V Leiden mutation, the risk jumps to 11%. Having one copy of the Prothrombin 20210 mutation raises the risk to 8.8%. In the unlucky few who have one copy of each of these mutations, the risk is a 32%. And in the extremely rare case that someone inherits two copies of both mutations, the risk of DVT/PE is 69%.

(This information applies only to those with European ancestry. Average risk numbers are different for other groups, and the genetic risk factors discussed here are not usually found in people with African or Asian ancestry.)

Other risk factors for DVT and PE include being overweight or obese, cancer and its treatment, pregnancy and childbirth, use of hormones for birth control or menopause, and smoking.

“We want to increase the awareness and knowledge of these potentially deadly conditions and encourage patients and health care providers to take the steps to prevent them,” Galson said.

For more information:

• Surgeon General’s Fact Sheet on Deep Vein Thrombosis and Pulmonary Embolism
• The Coalition to Prevent Deep-Vein Thrombosis
• Patient and Provider Guides from the Agency for Healthcare Research and Quality (also available in Spanish)

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