One of the kallikrein genes (KLK3) encodes Prostate Specific Antigen, a key biomarker for prostate cancer. A number of factors, both genetic and non-genetic, determine variation of serum Prostate Specific Antigen levels in the population. We have found KLK3 deletions in individuals with very low Prostate Specific Antigen levels, suggesting a link between abnormally reduced kallikrein gene 3 expression and deletions of kallikrein gene 3 (Rodriguez et al., 2013, Clin Chem. 59(1):234-44). We have also identified common deletions in the KLK3 gene in the 1958BC, and have also found in silico evidence for KLK3 deletions in the NBS cohort (Al-Ghamdi et al., 2013 [PhD thesis]), Rodriguez et al., (submitted).