From a new study:
"Patients homozygous for the rs4680 low-activity met allele (met/met), known to have high levels of dopamine, had the greatest placebo response. The high-activity val allele homozygous (val/val) patients had the lowest placebo response."
Met/met is AA. Val/val is GG.
Here's a link to the article.
http://www.cell.com/trends/molecular-me ... 71-4914(15)00043-X