The SMOFAM Study previously conducted model free linkage analysis with several nicotine dependence and tobacco use phenotypes (14). Swan et al found a maximal LOD score (MLS) of 2.7 on chromosome 6 for the Fagerström Test for Nicotine Dependence (FTND) and a MLS score of 2.7 on chromosome 6 for withdrawal severity (the summation of nine withdrawal symptom scores, rated on a 4-point Likert scale; 0, not at all to 3, severe, with range 0 to 27), with the FTND MLS found distal to the withdrawal severity MLS. The support interval for the FTND MLS covered a broad area of 34 centiMorgans (cM) (17), from 156–190 cM, while the support interval for withdrawal severity covered an overlapping but smaller region of 25 cM, from 148–173 cM. The more proximal support interval includes the mu opioid receptor (MOR) gene (OPRM1) locus.
