Detection of Genetic Variants of Haemophilia B with an Immunosorbent Technique

Abstract

S ummary . With an immunosorbent technique, we have found multiple genetic variants of haemophilia B. In one variant there is no detectable material that cross‐reacts with a human anti‐factor‐IX antibody. This variant is defined as negative for cross‐reacting material (CRM − ). There is also a CRM + variant in which the factor‐IX deficient plasma has the capacity to neutralize as much antibody as does normal plasma. There is an intermediate variety that neutralizes the specific antibody to a degree which is proportional to the factor‐IX clotting activity. This last group has been designated as having reduced cross‐reacting material (CRM R ). The CRM R group is probably heterogeneous, and it is likely that many genetic variants of haemophilia B exist.