While increased expression of haptoglobin was seen in patients with chronic graft-versus-host disease (GvHD)62, haptoglobin levels falling below lower limit of normal range is often associated with post-transplant thrombotic microangiopathy (TA-TMA) and autoimmune hemolytic anemia (AIHA)63–65. This evidence concerns the gene HP and Genetic thrombotic microangiopathy.