So far, the serum GFAP levels were only shown to be a potential biomarker in intracerebral haemorrhage and ischemic stroke [21,38] and to correlate with the disease severity in multiple sclerosis [39,40,41], Alzheimer’s disease [42] and NMOSD [43,44]. Here, GFAP is linked to early-onset autosomal dominant Alzheimer disease.