CALR and Venous thrombosis: Among patients with ET, those with a CALR mutation had a lower risk of thrombosis than did those with the JAK2 mutation.7,9,10 In a cohort of 144 patients with splanchnic vein thrombosis (SVT), the incidence of JAK2V617F mutation was 18.8%; CALR exon 9 mutations were not detected in any of the 144 SVT patients.