In addition, a trend towards reduced mRNA expression of peptide methionine sulfoxide reductase (MsrA), an enzyme converting methionine sulfoxide to methionine, and significantly diminished MsrA activity, to a much greater extent, has been detected in AD-affected brain regions, such as hippocampus, superior and middle temporal gyri, and inferior parietal lobule [138]. Here, MSRA is linked to Alzheimer disease.