dr. gahli'm just getting to the point where i'm really at my last leg. so this chance to come here to be evaluated was really a big deal for me. >> logan: four years ago, when dr. gahl created this program to help people like christine, there was nothing of its kind in the u.s. here in his lab, scientists search for links between rare, unknown diseases and genetics. as with most of his patients, he suspects christine davidson's own genetic make-up may be at the root of her illness. >> gahl: do you have a brother, sister? >> davidson: yeah, i have two brothers that are totally healthy, and two sisters that do have health problems. >> gahl: but not this? so you have four siblings, and your dad, all of them are available for blood from if we need it? >> davidson: yeah. >> logan: as part of her evaluation, christine must undergo a week of intense testing here at the clinical center of the national institutes of health. dr. gahl has a small staff and a small budget, $3.5 million out of the billions