The thing about a genetics lab is, you're never "done" with a family. If you find a mutation, you follow it through the generations and the far-flung third cousins. If you don't, you retest that family every time a new gene comes up that might be involved somewhere somehow in the pathology that led the family to you in the first place.
For these new genes, it's often important to know 'Yes, we looked for it. No, you don't have it.' Most of those results just stay in the family file. No need to be calling them in each time some negative result comes up.
More rarely, the result is 'Hey, there's this new gene out that we thought might be relevant, and it turns out...' Those are the ones that keep you interested as a scientist. There are families we've studied for ten years before hitting on the right gene.
Just recently, there was an unusual mutation in one of the major genes we study found in the Portugese, a mutation that could be missed by our standard techniques. So we developed a specific test for it, and then it was time to make the rounds of every case we had ever studied for that gene and gotten a negative result. Not just our patients of Portugese origin, but everyone. You never can be sure what happened generations ago. They're a traveling people, the Portugese.
1063 'yes we looked, no you don't have its' later, I'm finally done writing reports! I've been writing reports on DNAs we received twenty years ago. Reports for people who are now surely gone, but whose families are still concerned.
And yes, there was one positive result. One family for which we could finally figure out who's really at risk of breast cancer and whose risk is low. Yea!