Pedigree-wide analyses were conducted for the 22 autosomal chromosomes using MERLIN-REGRESS and the X chromosome using MINX (Abecasis et al., 2002). Multipoint linkage analyses were examined for the Younger and Older datasets. Data for both co-twins from MZ pairs were modelled in analyses (with zygosity identified), although the MZ relationship per se does not contribute to linkage. Post-hoc linkage analyses examined the effects of excluding individuals with the least alcohol exposure by dropping approximately 10% of the sample (8.3% for the Younger dataset and 7.6% for the Older) from the lower end of the sex and age adjusted distribution of consumption. Essentially, this subset were non-drinkers during the previous 12 month period (<1 drink per week), although many reported having dependence symptoms at some time during their lives (reported symptoms ranged 0–11, M = 1.4±2.8 and 1.3±2.7 for the Younger and Older datasets respectively).
