We observed associations between alcohol phenotypes and markers that localize to within or near genes of biological interest. Most notable is the association between Maxdrinks and the glutamate ionotropic receptor delta type subunit 1 gene (GRID1), which is involved in synaptic plasticity. GRID1 has been implicated in prior genetic studies of alcohol use outcomes: Chen et al. (2015) found that SNPs nominally associated with alcohol cue-elicited brain activation were enriched for markers mapping to genes, including GRID1, that are involved in synaptic long term depression. This gene was further implicated in comorbid alcohol dependence and depressive syndrome (Edwards et al., 2012), and in a study of alcohol problems in a population-based sample (Edwards et al., 2015). Glutamatergic receptor subunit mRNA, including GRID1, has been shown to be altered in the caudate within an alcoholic sample relative to controls (Bhandage et al., 2014). More generally, GRID1 has been associated at varying levels of significance with brain structure (Nenadic et al., 2012) and schizophrenia (Fallin et al., 2005; Treutlein et al., 2009b; Nenadic et al., 2012). Besides GRID1, top markers mapped to
