pair members who are discordant for cannabis use [294]. These hypotheses are further reinforced by 1) twin data that document strong shared genetic influences on frontal brain volumes and cognitive function measures [246, 247], 2) smaller head (and thus likely brain) sizes in individuals who go on to develop Alzheimer’s disease decades later [295], and 3) lower levels of educational attainment (and thus cognitive function) in individuals who go on to develop Alzheimer’s disease many years later [252, 253]. Little convincing prior evidence linked addiction liability directly with Alzheimer’s disease, although there are reasonably strong links between addiction vulnerability and the related, often-dementing neurodegenerative illness, Parkinson’s disease [296] (further reviewed in [297]). Identification of the genes documented here should lead to elucidation of features of addiction vulnerability that might arise preferentially from the “connectivity constellation” gene variants that also alter vulnerability to Alzheimer’s disease.
