Emerging evidence implicates impairments in working memory as a core feature of ADHD, which renders working memory as a potentially useful intermediate ADHD phenotype that may modulate the association between genes and clinical symptomatology (Castellanos & Tannock, 2002). Two key components of working memory are maintenance and manipulation; the ability to manipulate information in working memory is differentially weaker in individuals with ADHD relative to pure maintenance of information in an online cognitive state (Hale, Hoeppner & Fiorello, 2002). Manipulation is also weaker in unaffected siblings of children diagnosed with ADHD relative to typically developing children, further supporting its potential usefulness as an intermediate ADHD phenotype (Rommelse, Altink, Oosterlaan, Buschgens, Buitelaar & Sergeant, 2008).
