Associative studies are quite popular and yet logically they merely present odds and not cause and effect in the individual case. A study some years ago by Joe De Risi the acclaimed scientist in his San Francisco laboratory showed that a missing enzyme that suppresses viruses correlated to the prostate cancer he was finding in samples he used to test his sophisticated device that can spot any virus from one tissue sample. (Available for viewing on the TED network online) My point is that a test showing a familial lack of this enzyme  is a real biological linkage and that type of group needs to be tested for progression evidence not a random large group with varied biological backgrounds and profiles.