found when the LG and LA variants are compared (Lesch et al., 1996). There appears to be a weak positive association between the 5-HTTLPR S variant and increased AD risk (Feinn, Nellissery, & Kranzler, 2005). Unfortunately, earlier studies included in this meta-analysis and described later did not distinguish the two forms of the L variant and this may have diluted the significance of the results, particularly in studies that included African Americans, in whom the LG variant is at a high frequency.
