Even though prospective CS/ICs have been characterized by expression of specific markers, such as CD24, CD44, CD90, CD133, and ALDH1 (for review, see [18,19,20,21,22,23,24]), no common CS/IC marker has been identified so far and, for some CS/ICs, different markers have been proposed (Table 1). The gene discussed is ALDH1A1; the disease is Cowden syndrome 1.