Chunk #25 — 3. Insights and Limitations from GWAS of AD — 3.3 The Phenotypic and Genetic Complexity of AD — 3.3.1 Using Comorbidity to Understand Heterogeneity
One approach to understanding the phenotypic/etiological complexity of alcohol is to understand the nature of its relationship with other traits and to account for them in studies. Past studies show that individuals who use/misuse alcohol are also likely to use/misuse tobacco and other drugs (Palmer et al., 2009), thus pointing to a general liability for dependence across multiple substances (Palmer et al., 2012). Alcoholics are also more likely to be diagnosed with other psychiatric disorders, such as major depression or antisocial personality disorder (Edwards et al., 2012; Iacono et al., 2008; Sher et al., 2005). In fact, many psychiatric disorders are often comorbid with alcohol use and AD and in some instances, precede it (Elkins et al., 2006, 2007). For instance, we recently examined a sample of older adolescents and determined that those who exhibited high levels of DSM-IV CD symptoms and novelty seeking tendencies were more likely to exhibit high levels of alcohol, tobacco, and cannabis DSM-IV dependence symptoms during young adulthood (Palmer et al., 2011). To further complicate matters, AD is one component of the latent Externalizing (EXT)
