CHRNA4 and Parkinson disease: The deficit of some of the nAChR subunits in PD has been explicitly explored.28 The two predominant forms of the nAChR, the α4β2 and the α7 oligomers, are also strongly expressed in the striatum, accompanied by the α6β2 form.29 It is not clear whether other subunits are present in the heteromeric nAChRs.