(Reuters) -Biogen Inc’s gene therapy for an inherited retinal disease that leads to progressive vision loss did not meet the main goal of a study, a development that increases focus on an upcoming decision on its under-review Alzheimer’s drug. The experimental treatment, BIIB112, did not show significant improvement in a mid-to-late stage study in retinal sensitivity in patients with X-linked retinitis pigmentosa, a rare eye condition that has no approved treatments. Biogen is betting on gene therapies to diversify its portfolio as its top-selling multiple sclerosis drug, Tecfidera, faces increased generic competition and uncertainty over approval of its Alzheimer’s drug, aducanumab. It acquired BIIB112 through its $800 million deal for gene therapy company Nightstar Therapeutics, and recently signed a research collaboration with Capsigen to develop gene therapies for central nervous system and neuromuscular disorders. The trial results will likely remind investors of the high-risk nature of Biogen’s pipeline, RBC Capital Markets analyst Brian Abrahams said, despite the program having a low relevance to the company’s future revenue. “Investor focus likely remains squarely on aducanumab’s PDUFA (FDA’s decision date) next month.” Aducanumab, seen as a potential blockbuster if approved, has had a bumpy regulatory road. The U.S. Food and Drug Administration (FDA) is set to decide on the drug by June 7 after delaying it from March and the regulator’s outside experts voted against aducanumab last year. BIIB112 showed positive trends in improving visual sharpness under low light conditions and Biogen is analyzing the complete data to decide the next steps. The company’s shares were down 1.6% in a higher broader market. The study data is the latest setback in the gene therapy field in recent months. In March, Roche stopped late-stage trials of its gene therapy for Huntington’s disease after an independent data monitoring committee questioned whether the drug’s benefits outweighed its risks. Reporting by Mrinalika Roy in Bengaluru; Editing by Arun Koyyur and Sriraj Kalluvila Our Standards: The Thomson Reuters Trust Principles.