Polymorphisms on the OPRMI mu-opioid receptor gene (A118G) and DRD2 dopamine receptor gene (Taq1A A1) have been found in both samples of BED and SUDs, and may increase their vulnerability to the reward characteristics of food and substances (Davis et al., 2009; Wang, Volkow, Thanos & Fowler, 2004). Here, OPRM1 is linked to X-linked cone dysfunction syndrome with myopia.