When Pris and Roy seek out the genetic designer J. F. Sebastian, they discover that he has a glandular condition called "Methuselah Syndrome," which causes him to age prematurely. Naturally, they see that he's in the same boat as they are—since they also have a set time limit on their lifespans—and they try to leverage that for aid and empathy. Sebastian ends up helping them, though probably more out of fear than anything else. It doesn't work out well for him, in the end: Roy kills him, off-screen.
The fact that Sebastian's disease is called "Methuselah Syndrome" fits in with some of the biblical echoes in Blade Runner, since Methuselah is the character in the Hebrew Bible who is said to have lived the longest, hitting the ripe old age of 969. This makes the title of the disease somewhat ironic, since it involves dying sooner rather than later.