GFAP and Tay-Sachs disease: Astrocytosis as measured by glial fibrillary acidic protein immunostaining in the TSD+AAV_CSF_ICV_CM-LIT cohort was like that in the WT control at all ages but progressed like untreated TSD in the forebrain of the TSD+AAV_CSF_CM_LIT sheep 39 months after treatment (Supplemental Figure 9).