The FDA is expected to announce its decision on REGENXBIO Inc.’s (RGNX) Clemidsogene lanparvovec for mucopolysaccharidosis type II (MPS II), or Hunter syndrome, on February 8, 2026.MPS II is a rare, X-linked recessive disease caused by a deficiency in the lysosomal enzyme iduronate-2-sulfatase (IDS), required for the degradation of glycosaminoglycans (GAGs). Accumulation of GAGs causes systemic symptoms, neurodegeneration and leads to early death. In severe forms of the disease, early developmental milestones may be met; however, developmental delay becomes readily apparent by 18 to 24 months. In the U.S., Takeda’s Elaprase, an enzyme replacement therapy that requires repeated, lifelong infusions, is the only approved treatment for MPS II.Clemidsogene lanparvovec, also known as RGX-121, is designed to deliver the human iduronate-2-sulfatase (IDS) gene to the central nervous system. Delivery of the IDS gene within cells in the CNS could provide a permanent source of secreted iduronate-2-sulfatase (I2S) protein beyond the blood-brain barrier, allowing for long-term cross-correction of cells throughout the CNS. The RGX-121 expressed protein is structurally identical to normal I2S.If approved, Clemidsogene lanparvovec could be the first gene therapy and one-time treatment for MPS II.RGNX closed Tuesday’s (Jan.27, 2026) trading at $13.41, down 3.21%.