POSTN and Alzheimer disease: Although periostin is well-known as a useful biomarker for various diseases, many studies in the past decade have focused on allergic and fibrotic diseases, and reported periostin levels as a valuable biomarker, with its levels correlating with disease severity, prognosis and responsiveness to the treatment in atopic dermatitis (AD) [17,21,22], asthma [23,24,25,26] and idiopathic pulmonary fibrosis (IPF) [27,28,29,30].