FOP( fibroblast growth factor receptor 1 oncogene partner) is a largely hydrophilic protein postulated to be a leucine-rich protein family member. FOP contains 1 LisH domain. A t(6;8)(q27;p11) chromosomal translocation, fusing FOP gene and the fibroblast growth factor receptor 1 (FGFR1) gene, has been found in cases of myeloproliferative disorder. The resulting chimeric protein contains the N-terminal leucine-rich region of this encoded protein fused to the catalytic domain of FGFR1. FOP gene is thought to play an important role in normal proliferation and differentiation of the erythroid lineage. Alternatively spliced transcript variants that encode different proteins have been identified.