subjects in the computation of correlations and from inspection of the change in heritability estimates when age of onset was viewed continuously (see Figure 2 and 3). Concordant early-onset twin pairs (both reported age at 1st drink at 14 years or younger) had an MZ and DZ (combined across sexes) correlation for AD symptoms of 0.36 and 0.12 respectively. MZ and DZ correlations in concordant late-onset (both twins reported age at 1st drink at 15 years of older) were 0.33 and 0.17 respectively while in discordant pairs, MZ and DZ correlations were 0.34 and 0.14 respectively. Therefore, heritability in the concordant early, concordant late and discordant pairs suggests greater heritable influences in those with early age at 1st drink.
