rs5751876

rs5751876 is a synonymous tag variant in the ADORA2A gene, which encodes the adenosine A2A receptor that caffeine blocks in the brain to produce its stimulant effects. It is used here for one phenotype only: caffeine-induced anxiety and jitters, where T-allele carriers — particularly T/T homozygotes — report more jitteriness and nervousness in randomized double-blind caffeine-versus-placebo challenges. Note the allele frequencies run opposite ways by ancestry (C is the major allele in Europeans at ~0.61, T the major allele in African-ancestry groups at 0.68), so neither should be described as 'the minor allele'.