This study is totally voluntary. Any participant may withdraw at any time by contacting one of these three people. Once notified, we will discard what blood or DNA samples may be remaining and make sure that you are not contacted in the future concerning follow-up studies. If your DNA has already been analyzed for certain DNA differences and the data have been statistically analyzed, we will not be able to remove the data from our databases, but we will not give your name and contact information to other scientists for future studies. If your name and contact information have already been passed on, we will contact those scientists and ask that your name be removed from their list.