Based on all these samples, the frequency of the protective 504lys allele was 14% (overall population estimate) but varied widely across different populations and disease statuses: high in the Asian normal populations 23% (1% – 53%), lower in affected subjects, 7% (0 – 23%); very low in Mexican Americans (1%); and undetected in the European-ancestry populations. Of the 53 studies included, 52 studies showed lower 504lys allele frequency in cases than in controls. Drug dependence as a primary diagnosis and non-Asian samples were considered as extra information for comparison (i.e., allele frequency calculation), and thus excluded from the following meta-analysis.
