CADM2 (cell adhesion molecule 2) encodes a synaptic cell adhesion molecule expressed at very high levels in many brain regions. In a gene-based analysis, CADM2 was associated with alcohol consumption in the UK Biobank, as are several SNPs in CADM2 (rs13078384, rs1376935, rs67028245) (Clarke et al., 2017). CADM2 is also associated with other psychological diseases and traits, including sensation seeking, drug experimentation, substance use involvement, and attention-deficit/hyperactivity disorder (Sanchez-Roige et al., 2019) and lifetime cannabis use (Pasman et al., 2018, Stringer et al., 2016). FRMD4A (FERM Domain Containing 4A), also expressed in multiple regions of the brain, is involved in regulating epithelial cell polarity. Polymorphism in FRMD4A is associated with nicotine dependence (Yoon et al., 2012) and as a risk locus for Alzheimer’s disease (Lambert et al., 2013). PLK2 (polo like kinase 2) encodes a member of the polo family of serine/threonine protein kinases and has a role in normal cell division. It is expressed in multiple regions of the brain (GTEx). Two studies have reported that PLK2 expression is significantly upregulated in human Alzheimer’s disease brain tissue (Mbefo et
