MAPK3 and early-onset autosomal dominant Alzheimer disease: Furthermore, ERK1/2 has been proposed to represent a potential diagnostic biomarker in Alzheimer’s disease: Alterations in ERK1/2 phosphorylation in response to bradykinin have been observed in cultured skin fibroblasts from Alzheimer’s disease patients22, 23, 24, and elevated levels of total ERK1/2 protein in cerebrospinal fluid were reported25.