Recently, Wessel et al. resequenced 10 nAChR subunit genes and found a significant association between rare variants in CHRNA4 and FTND score (44). However, due to the small sample size in that study (N=430), they observed a total of only 21 rare variants, including 5 nonsynonymous rare variants in CHRNA4. Because they were unable to perform more detailed analyses on nonsynonymous variants, the results of their study were not conclusive. In contrast, we used a two stage case-control design. When results from the two stages were combined, a total of 169 rare variants of 59 types were observed in exon 5. Among them, we found a total of 63 nonsynonymous rare variants of 27 types. This sample size proved to be adequate to provide significant evidence that functional nonsynonymous rare variants located in the cytoplasmic loop of the α4 subunit play a protective role in ND, especially in the AA population.
