Identification of cell adhesion molecule genes, which are represented in several of the above mentioned gene classes (Table 2) continues to focus our attention on roles in addiction for mechanisms for establishing and regulating neuronal connections [50]–[52]. These data accord well with prior results that link substance dependence to 5′ NrCAM variants that alter levels of expression and to 3′ NRXN3 variants that alter relative levels of splicing isoforms [45], [53]. It is important to note that these cell adhesion genes are generally large, providing more opportunities for allelic variants that could alter their functions in a number of fashions. It is interesting to note that recent analyses of all reported genome wide association datasets also identified overrepresentation of cell adhesion molecule genes [54].
