Against these data, however, are the observations that ET and PV patients can have a normal life span, and that cross-sectional studies employing high-resolution SNP arrays [155,178] have demonstrated that, when 9pUPD was excluded, JAK2 V617F-positive and -negative chronic phase MPN patients did not differ greatly with respect to chromosomal aberrations, and usually had fewer than three mutations, with many patients only expressing only JAK2 V617F [81,178]. Here, JAK2 is linked to acquired polycythemia vera.