WASHINGTON — Researchers have identified a gene underlying Elephant Man’s disease, which afflicts 100,000 Americans and can cause grotesque tumors, crippling and learning defects.

Discovery of the gene, experts said Thursday, is a vital step toward developing therapy for the now-untreatable genetic disorder that has puzzled doctors for decades.

Researcher Dr. Francis Collins said it might be years before the discovery results in drugs or other direct treatment, but that diagnostic tests to identify those who carry the defective gene may be developed rather quickly.

Scientists at the University of Michigan and the University of Utah, working independently, found the neurofibromatosis, or NF, gene at virtually the same time.

For Collins, leader of the Michigan group, it was the second major gene discovery in 11 months. He was a co-discoverer of the cystic fibrosis gene in August.

“We have pried open the black box of neurofibromatosis and are peering inside,” Collins said at a news conference.

The University of Utah co-discoverer of the gene is Dr. Raymond White, whose paper will be published Friday in the journal Cell. Collins is publishing Friday in Science, the journal of the American Association for the Advancement of Science.

Neurofibromatosis is a genetic disorder that strikes about one in every 4,000 newborns.

For two-thirds of the patients, the symptoms are mild skin discoloration. For the rest, NF causes tumors that can pop up anywhere in the body, but always on nerve tissue.

The tumor growth can raise large globular masses on the face, trunk or limbs, and can distort growing bones, causing crippling or misalignment of the skull.