The invention relates to a new, more potent, coagulation factor IX (FIX) expression cassette for gene therapy of haemophilia B (HB). Disclosed is a vector for expressing factor IX protein, the vector comprising a promoter, a nucleotide sequence encoding for a functional factor IX protein and an intron sequence, wherein the intron sequence is positioned between exon 1 and exon 2 of the nucleotide sequence encoding for a functional factor IX protein, and wherein the intron sequence has at least 80% identity to the sequence of SEQ ID NO. 1 as disclosed herein.本發明係有關於一種新穎、更有效力的凝血第九因子(FIX)表現匣用於B型血友病(HB)之基因療法。揭示一種用於表現第九因子蛋白質之載體，該載體包含一啟動子、一編碼功能性第九因子蛋白質的核苷酸序列及一內含子序列，其中該內含子序列係位於該編碼功能性第九因子蛋白質的核苷酸序列之外顯子1和外顯子2之間，以及其中該內含子序列與如此所揭示的序列辨識編號1的序列有至少80%的同一性。
