that may have more homogeneous etiologies (e.g., early onset alcohol dependence) (Edenberg, Xuei et al. 2007); and broader phenotypes that may jointly reflect a shared etiology (e.g., by studying general externalizing or internalizing disorders) (Hettema, An et al. 2006; Dick, Aliev et al. 2008). The study of endophenotypes, or intermediary phenotypes thought to be closer to the underlying genetic architecture than are clinical diagnoses, has also received great attention (Almasy and Blangero 2001; Gottesman and Gould 2003; Cannon and Keller 2006; Dick, Jones et al. 2006). However, one area that has remained relatively neglected is the evaluation of longitudinal phenotypes, that is, patterns of change in behavior and physiology over specified time periods. Here we report analyses that use longitudinal measures of alcohol-related outcomes to characterize how genetic risk unfolds across developmental stages.
