This BRCA1 downregulation does not seem to be dependent on different fractions of JAK2 V617F+ and JAK2 wild-type progenitors in individual cell cycle stages [82], but rather it seems to be an inherent feature of proliferating JAK2 V617F+ PV progenitors, similarly to BRCA1 deficiency in BCR-ABL-proliferating CP-CML [60]. Here, JAK2 is linked to chronic myelogenous leukemia, BCR-ABL1 positive.