The subjects used in our replication sample were from the Mid-South Tobacco Family (MSTF) study with either African-American (AA) or European-American (EA) origin. They were recruited primarily from Tennessee, Mississippi, and Arkansas during 1999-2004. Proband smokers were required to be at least 21 years of age, to have smoked for at least the last 5 years, and to have consumed an average of 20 cigarettes per day for the last 12 months. Once a proband was identified, siblings and biological parents were recruited full sibs per family. Detailed information of the recruitment and characteristics of study participants have been reported (Li 2008; Li et al. 2005,2006; Ma et al. 2005). Together, a total of 200 EA and 402 AA families were recruited. Informed consent was obtained from all participants and approval from the appropriate Institutional Review Boards.
