required sample size. Thus, these two genes are considered to have only weak evidence of involvement in ND and therefore are not included in Figure 1 and Table 2. Besides nAChR subunit genes, two cholinergic receptors, muscarinic 1 (CHRM1) and 2 (CHRM2), were found to be significantly associated with CPD and FTND, respectively.90, 101 They are within nominated linkage peaks as well.34 However, because of the inadequacy of knowledge of their biological functions, they have been less investigated.
