Kimberly Doheny, lab director at the Center for Inherited Disease Research at Johns Hopkins University, poses next to a DNA scanner, Friday, March 21, 2008, in Baltimore. The scanners, blue boxes each about twice as big as a desktop printer, will reveal what DNA 'letter' appears in more than 580,000 spots in the genetic material, said Doheny. (AP Photo/Rob Carr)AP - Scientists are scanning human DNA with a precision and scope once unthinkable and rapidly finding genes linked to cancer, arthritis, diabetes and other diseases.