When a pregnant woman had her blood sampled back in 1972, doctors discovered it was mysteriously missing a surface molecule found on all other known red blood cells at the time. After 50 years, this strange molecular absence finally led researchers from the UK and Israel to describe a new blood group system in humans. "It represents a huge achievement, and the culmination of a long team effort, to finally establish this new blood group system and be able to offer the best care to rare, but important, patients," UK National Health Service hematologist Louise Tilley says, after nearly 20...