GFAP and X-linked adrenoleukodystrophy: However, this trend towards increased blood GFAP did not reach statistical significance for either asymptomatic X-ALD (model estimate of mean ratio: 1.6, CI: 0.8–3.2; p = 0.184, linear mixed model) or for AMN patients (model estimate of mean ratio: 1.4, CI: 0.8–2.4; p = 0.221).