STAT1 and essential thrombocythemia: However, PTPN6 has been significantly increased only in JAK2V617F heterozygous ET patients. STAT1 and STAT2 gene expression have been increased in heterozygous ET and PV patients, while STAT3 only in homozygous PV patients. STAT5A has been significantly decreased in ET and PMF with no JAK2V617F mutation as well as in homozygous PV patients (Table 2).