You may think that you know your blood type, but did you know that there are in fact 35 blood group systems in humans? These include well-known systems such as ABO and the Rh system (formerly known as 'Rhesus').
Advances in research technologies in the past few years have made it possible to identify three new blood group systems: Langereis and Junior, identified in 2012, and Vel, discovered a year later in 2013. All three were named after the patients in whom they were first discovered.
In Japan, there are around 2,500 people who are Langereis negative. Although Langereis-negative people have been found across the globe, their total numbers aren't known. Also in Japan, there are some 50,000 people who are Junior negative. This blood type is thought to be rarer in the rest of the world, although there are some Junior-negative people among European gypsy communities. And around 400,000 people – mostly in Europe and the USA – are thought to be Vel negative.
Pinning down the antigens and antibodies in each system – and developing a rapid in-hospital test for them – was an important step for transfusion medicine, because all three are 'clinically significant'. This is because they will cause a dangerous reaction if transfused into a patient who has made an antibody against 'positive' blood.
The antibody people make against Vel, designated 'anti-Vel', is the most dreaded. Transfusion doctors have known of its existence since the early 1950s, when 'Patient Vel', a 66-year-old woman, violently rejected the blood she had received.
However, the antibody was such a scarce resource – not everyone who is Vel negative will make it, even on exposure to positive blood – that Vel-negative blood was impossible to screen for on more than a small scale. That all changed last year when two international teams separately identified the genetic mutation responsible for the missing antibody: patient and donor blood can now be screened for it with a simple DNA test.
It's still possible that other blood group systems or antigens – so rare they haven't yet surfaced – may emerge. Nicole Thornton, Head of Red Cell Reference at the International Blood Group Reference Laboratory (IBGRL) in Filton, near Bristol in England, thinks there are undiscovered systems out there. Professor Bryan Ballif – who with colleagues identified the molecular basis of Langereis and Junior, and who was in one of the teams who developed the test for Vel – thinks there could be as many as ten.