On the basis of these observations, it can be stated that the nicotine-induced increase of HINT1 is mediated through specific nAChR subtypes, such as α4β2* (where * denotes the possible incorporation of additional subunits) or α7, the major nAChR subtypes in the brain, which have been shown to mediate behaviors associated with ND. Here, CHRNA4 is linked to Norrie disease.