For example, the first studies reporting the overexpression of StAR, HSD3β2, aromatase, HSD17β1, ERβ, and GPER all used OE or AD tissue samples (Brandenberger et al., 1999; Fujimoto et al., 1999; Attar et al., 2009; Mehasseb et al., 2011; Samartzis et al., 2012), due, likely, to less prevalent occurrence and thus the difficulty in getting DE samples. This evidence concerns the gene ESR2 and Alzheimer disease.