In the catch-all part, after showing suggestive association in the first ND GWAS,92 neurexin 1 (NRXN1) association has been replicated in two independent studies with more than 2,000 subjects of three ancestries: African, Asian, and European.93, 94 Although neurexin 3 (NRXN3) also showed a significant association with the risk of being a smoker,95 this finding has not been verified in any other ND samples, and NRXN3 is not within any detected linkage peak.34 Neurexins are cell-adhesion molecules that play a key role in synapse formation and maintenance and have been implicated in polysubstance addiction.96
