ARPP21 and Intellectual disability: ARPP21 encodes a cAMP-regulated phosphoprotein, enriched in the basal ganglia and cerebellum, that has a central role in the integration of neurotransmitter inputs into striatal medium spiny neurons.61 Intriguingly, a deletion encompassing this gene segregated with syndromic intellectual disability in a multiply affected pedigree.62 Similarly, we found that the minor (T) allele of rs2568955 was associated with poorer cognitive performance, and this allele is associated with greater expression of RPL31P12 (Supplementary Figure S2).