These results suggest that these markers of astrogliosis, CSF GFAP and S100b are progressively expressed with accumulating Aβ pathology and that they track a different aspect of astroglial response to Alzheimer’s disease pathology than YKL-40, which was only found to be elevated in the A + T+ stage. The gene discussed is GFAP; the disease is early-onset autosomal dominant Alzheimer disease.