UGT2B17 encodes the protein UDP glucuronosyltransferase
[PMID 18334593] Deletion of both copies of this gene alters testosterone metabolism making steroid use undetectable.
The first page of this thesis claims that the deletion allele has a frequency of 4.8% in Swedes but is completely absent in Koreans. While its abstract claims "it is a common polymorphism with an allele frequency of 29 % in Swedes and 78 % in Koreans." It is interesting to note that this was included in User:Watson snp data despite it's 100% CEU frequency.