GFAP and Alzheimer disease: Also, in the comparison between DS with and without AD, across three studies involving 172 DS with AD individuals and 658 without AD individuals, the SMD was 1.98 (95% CI [1.78, 2.18], z = 19.86, p < 0.00001), showing a significant increase in plasma GFAP levels in the DS with AD group, with no heterogeneity (I2 = 0%, p = 0.89).