CALR exon 9 mutations in idiopathic splanchnic vein thrombosis in an Australian cohort

Splanchnic Vein Thrombosis in Myelofibrosis-An Underappreciated Hallmark of Disease Phenotype

Splanchnic vein thrombosis (SVT) encompasses thrombosis in the vessels of the splanchnic basin and has a relatively rare occurrence with a reported frequency in the general population of 1-2%. An episode of seemingly unprovoked SVT almost always triggers a diagnostic work-up for a Philadelphia chromosome-negative myeloproliferative neoplasm (MPN), since atypical site thrombosis is a hallmark of MPN-associated thrombophilia. Primary myelofibrosis (PMF) is a rare MPN with an estimated incidence between 0.1 and 1/100,000 per year. Although prothrombotic tendency in PMF is not envisioned as a subject of specific therapeutic management, unlike other MPNs, such as polycythemia vera (PV) and essential thrombocythemia (ET), thrombotic risk and SVT prevalence in PMF may be comparably high. Additionally, unlike PV and ET, SVT development in PMF may depend more on procoagulant mechanisms involving endothelium than on blood cell activation. Emerging results from registry data also suggest that PMF patients with SVT may exhibit lower risk and better prognosis, thus highlighting the need for better thrombotic risk stratification and identifying a subset of patients with potential benefit from antithrombotic prophylaxis. This review highlights specific epidemiological, pathogenetic, and clinical features pertinent to SVT in myelofibrosis.

Prevalence of CALR mutations in splanchnic vein thrombosis: A systematic review and meta-analysis

BACKGROUND

The prevalence of calreticulin (CALR) mutations in splanchnic vein thrombosis (SVT) varies among studies. The role of routine screening for CALR mutations in SVT patients remains a debate.

AIM

To synthesize the prevalence of CALR mutations according to the different types (i.e., Budd-Chiari syndrome [BCS] and portal vein thrombosis [PVT]) and characteristics (i.e., with and without myeloproliferative neoplasms [MPNs] and JAK2V617F mutation) of SVT patients.

METHODS

Eligible studies were searched by the PubMed and Embase databases. The study quality was assessed according to the STROBE checklist. The proportion of CALR mutations was pooled by using a random-effects model. The heterogeneity and publication bias were calculated.

RESULTS

Eleven papers were included. The study quality was moderate to high. The pooled proportion of CALR mutations was 1.21%, 1.41%, and 1.59% in SVT, BCS, and PVT patients, respectively; 1.52%, 1.03%, and 1.82% in these patients without JAK2V617F mutation, respectively; 3.71%, 2.79%, and 7.87% in these patients with MPN, respectively; and 15.16%, 17.22%, and 31.44% in these patients with MPN but without JAK2V617F mutation, respectively. Only the meta-analysis examining the prevalence of CLAR mutations in BCS patients with MPN but without the JAK2V617F mutation showed statistically significant heterogeneity. Statistically significant publication bias was seen only in the meta-analysis examining the prevalence of CALR mutations in SVT patients without the JAK2V617F mutation.

CONCLUSION

Screening for CALR mutations may have a role in SVT patients with a high probability of MPN in whom the JAK2V617F mutation has been excluded.

Selective testing for calreticulin gene mutations in patients with splanchnic vein thrombosis: A prospective cohort study

BACKGROUND AND AIMS

Myeloproliferative neoplasms (MPN) are the leading cause of splanchnic vein thrombosis (SVT). Janus kinase 2 gene (JAK2)^V617F mutations are found in 80 to 90% of patients with SVT and MPN. Mutations of the calreticulin (CALR) gene have also been reported. However, as their prevalence ranges from 0 to 2%, the utility of routine testing is questionable. This study aimed to identify a group of patients with SVT at high risk of harboring CALR mutations and thus requiring this genetic testing.

METHODS

CALR, JAK2^V617F and thrombopoietin receptor gene (MPL) mutations were analysed in a test cohort that included 312 patients with SVT. Criteria to identify patients at high risk of CALR mutations in this test cohort was used and evaluated in a validation cohort that included 209 patients with SVT.

RESULTS

In the test cohort, 59 patients had JAK2^V617F, five had CALR and none had MPL mutations. Patients with CALR mutations had higher spleen height and platelet count than patients without these mutations. All patients with CALR mutations had a spleen height ⩾16cm and platelet count >200×10⁹/L. These criteria had a positive predictive value of 56% (5/9) and a negative predictive value of 100% (0/233) for the identification of CALR mutations. In the validation cohort, these criteria had a positive predictive value of 33% (2/6) and a negative predictive value of 99% (1/96).

CONCLUSION

CALR mutations should be tested in patients with SVT, a spleen height ⩾16cm, platelet count >200×10⁹/L, and no JAK2^V617F. This strategy avoids 96% of unnecessary CALR mutations testing. Lay summary: Mutations of the CALR gene are detected in 0 to 2% of patients with SVT, thus the utility of systematic CALR mutation testing to diagnose MPN is questionable. This study demonstrates that CALR mutations testing can be restricted to patients with SVT, a spleen height ⩾16cm, a platelet count >200×10⁹/L, and no JAK2^V617F. This strategy avoids 96% of unnecessary CALR mutations testing.