nephew with downs syndrome, and i'm looking on the alzheimer's.org web site, and they mentioned how virtually 100% of adults with downs syndrome by age 40 will have evidence of the tangles associated with alzheimer's. >> uh-huh. >> now, what are the issues regarding -- wow, this is a group of kids, adults who are at risk, 100% at risk for a terrible condition. >> right. >> but there's other issues involved as well. what are your thoughts about this? how do we make stuff available for folks credibly at risk for such a terrible disease? >> yes. well, with alzheimer's there are a number of problems. the basic rob is we still don't -- problem is we still don't understand the disease well enough and the interventions that have been tried when people are already demeanted have failed to work. >> as i gather, though, the problem is predicting at an earlier stage those at risk, correct? >> that's correct. if you want to intervene early. we recently issued a draft guidance saying, okay, if you want to intervene earlier, we would accept an end point that is cog thinktive testing. >> i accept that, but how do you decide which population is such at high risk? if you had a control group, only