A prospective study examining genetic predisposition for transplant‐associated thrombotic microangiopathy (TA‐TMA) in HSCT recipients demonstrated that 65% of patients with TA‐TMA had genetic variants in at least one complement gene as compared with 9% of patients without TA‐TMA (P < 0.0001) using a hypothesis‐driven 17‐gene panel including the complement factors C3, factor B (FB), C5, FP, FD, FI, FH, FH‐related (FHR)1, FHR3, FHR4, FHR5, decay accelerating factor (DAF/CD55), CD59, membrane cofactor protein (MCP/CD46), and C4BPA (Jodele et al., 2016). The gene discussed is CD55; the disease is thrombotic microangiopathy.