The first marker we selected was the transmembrane glycoprotein involved in cell-to-cell interactions, CD44, since the first PCa CSCs ever isolated were CD44+ (Collins et al., 2005), and CD44+ PCa cells isolated from tumors were previously reported to be more tumourigenic and metastatic in comparison to CD44– cells, also exhibiting many other stem-like properties (Patrawala et al., 2006). The gene discussed is CD44; the disease is posterior cortical atrophy.