Genome-wide two-point parametric LOD scores for maximum number of cigarettes smoked per day are shown in Figure 1 (upper graphs) for both the unadjusted trait and for sex- and age-adjusted residuals (age and sex were significant covariates in linear regression, p < 0.001). There were two LOD scores greater than 1.0 in unadjusted analyses; one on chromosome 2 at 70.32 cM (LOD = 1.98) and the other on chromosome 17 at 66.85 cM (LOD = 1.52) (Table 1). Adjustment for sex and age did not appreciably change these results. However, additional peaks in sex- and age-adjusted analyses were seen on chromosome 15 at 65.52 cM (LOD = 1.09) and on chromosome 20 (consecutive markers at 70.51 and 84.62 cM, LODs = 1.30 and 1.02, respectively). With the additional inclusion of year at smoking maximum number of cigarettes, chromosome 20 LOD score peaks remained, however chromosome 2 and 17 peaks seen in unadjusted LOD score analysis were reduced (Table 1).
