JPMorgan analyst Michael Weinstein expects BioMarin (BMRN) in the coming days to announce that it treated the first hemophilia A patient with gene therapy in the U.K. For Baxalta (BXLT), the implications of BioMarin's first-in-man experience could be significant, Weinstein tells investors today in a research note. Should BioMarin report success over the next 3-6 months, the sustainability concerns around Baxalta’s hemophilia A business "go up considerably," creating an overhang on shares, the analyst believes. He keeps a Neutral rating on Baxalta with a $33 price target. Weinstein points out that Baxalta's Hemophilia business posted sales of $3.7B last year, equaling 62% of the company's revenue and 79% of profits. The company was recently spun off from Baxter (BAX).