JAK2 46/1 haplotype predisposes to splanchnic vein thrombosis-associated BCR-ABL negative classic myeloproliferative neoplasms.

The germline constitutive JAK2 haplotype, called GGCC or 46/1, s a susceptibility factor for BCR-ABL negative classic myeloproiferative neoplasms (MPNs), [1]. The mechanisms linking the aplotype block and the acquired MPN remain unclear. Two ypotheses have been proposed: the “hypermutability” of the chroosome region that could facilitate the arising of typical MPN omatic mutations [2], or the “fertile ground hypothesis” that could onfer selective advantage to cells carrying the 46/1 haplotype [3]. Splanchnic vein thrombosis (SVT), is variably associated with PNs, occurring both during the course of well defined MPNs, and, ore often, as the event leading to the diagnosis of MPN; the cateorisation of SVT-associated MPNs can be difficult, since the MPN henotype is frequently masked. In this study we sought to clarify the potential role of 46/1 hapotype in the etiology of SVT. Patients were diagnosed at the IRCCS Policlinico S. Matteo, Pavia, he IRCCS Ospedale Maggiore Policlinico, Mangiagalli and Regina lena, Milan, and the Azienda Ospedaliera Universitaria Careggi, lorence, according to the WHO criteria. Besides the diagnoses of T, PV, and PMF (prefibrotic and fibrotic type) we included the catgory of unclassifiable MPN to encompass cases that had a defined linical, laboratory and morphological features of a MPN but failed o meet the criteria for any of the specific MPN entities, or that resent with features that overlap 2 or more of the MPN categories ccording to 2008 WHO criteria [4]. The policies for collection of blood samples were approved by he institutional review board of the IRCCS Policlinico S. Matteo oundation, and all patients gave written consent. JAK2V617F mutation analysis was performed by allele speific PCR or real-time quantitative PCR on genomic DNA purified rom peripheral blood granulocytes with a commercial kit (Qiagen, ilden, Germany). Screening for the 46/1 haplotype was performed n the same DNA, assessing the tag SNP rs12343867 that is in comlete linkage disequilibrium with this haplotype. This SNP consists n a T to C shift, with the C allele associated with the 46/1 haplotype. nalysis was performed by a PCR reaction followed by HpyCH4IV nzyme (New England Biolabs, Hitchin, UK) digestion: the C allele ives origin to 174 and 120 bp fragments, whereas the T allele emains undigested (294 bp fragment); fragments were separated n a 3% agarose gel. The second approach was based on an allelic iscrimination assay using a commercially available RT-PCR SNP enotyping assay (No. C 31941689 10, Applied Biosystems, Foster ity, CA, USA; http://www2.appliedbiosystems.com) and the ABI RISM 7300 Detection System. For statistical analysis, the CC, TT r CT SNP genotype variants were considered as ordered categorcal variables and the chi-square or Fisher’s exact test (two tailed)