Runx1 P2 promoter activity starts early during hematopoietic development and is detected in HE, in which it is the sole active Runx1 promoter in mice (Bee et al., 2009; Sroczynska et al., 2009a) indicating that the RUNX1B isoform is responsible for the initiation of EHT. The gene discussed is RUNX1; the disease is hereditary elliptocytosis.