The current GSMA, which included 3404 families with 10,253 subjects, has identified many regions with varying degrees of evidence of linkage for smoking behavior. In the primary 30 cM GSMA of combined smoking behavior, genomewide suggestive linkage was detected at chromosome 17q24.3–q25.3. The fact that we did not identify any bins with genomewide significant evidence for linkage in the primary analysis might imply the possible relatively higher genetic heterogeneity due to a variety of different smoking behaviors and sample ancestry. Although only nominal significance was detected in the primary GSMA for the FTND, genomewide suggestive linkage was observed in 5q33.1–5q35.2 by shifting the bin boundary 15 cM in a secondary analysis of European-ancestry samples. Subgroup analysis of the MaxCigs24 phenotype identified numerous linkage signals; this might be attributable to the improved power from the increased homogeneity of both the phenotype and sample ancestry. For example, a genomewide significant linkage in bin 20.3 (20q13.12–q13.32) was identified, and the adjacent bin 20.2 (20p12.1–q13.12) showed suggestive linkage, providing more support for a true linkage signal in this region. Eleven regions with both PSR
