-- The most infamous feud in American folklore, the long-running battle between the Hatfields and McCoys, may be partly explained by a rare, inherited disease that can lead to hair-trigger rage and violent outbursts.

Dozens of McCoy descendants apparently have the disease, which causes high blood pressure, racing hearts, severe headaches and too much adrenaline and other "fight or flight" stress hormones.

No one blames the whole feud on this, but doctors say it could help explain some of the clan's notorious behavior.

"This condition can certainly make anybody short-tempered, and if they are prone because of their personality, it can add fuel to the fire," said Dr. Revi Mathew, a Vanderbilt University endocrinologist treating one of the family members.

The Hatfields and McCoys have a storied and deadly history dating to Civil War times. Their generations of fighting over land, timber rights and even a pig are the subject of dozens of books, songs and countless jokes. Unfortunately for Appalachia, the feud is one of its greatest sources of fame.

Several genetic experts have known about the disease plaguing some of the McCoys for decades, but kept it secret. The Associated Press learned of it after several family members revealed their history to Vanderbilt doctors, who are trying to find more McCoy relatives to warn them of the risk.

One doctor who had researched the family for decades called them the "McC kindred" in a 1998 medical journal article tracing the disease through four generations.

"He said something about us never being able to get insurance" if the full family name was used, said Rita Reynolds, a Bristol, Tenn., woman with the disease. She says she is a McCoy descendant and has documents from the doctor showing his work on her family.

She is speaking up now so distant relatives might realize their risk and get help before the condition proves fatal, as it did to many of her ancestors.

Back then, "we didn't even know this existed," she said. "They just up and died."

Von Hippel-Lindau disease, which afflicts many family members, can cause tumors in the eyes, ears, pancreas, kidney, brain and spine. Roughly three-fourths of the affected McCoys have pheochromocytomas _ tumors of the adrenal gland.

The small, bubbly-looking orange adrenal gland sits atop each kidney and makes adrenaline and substances called catecholamines. Too much can cause high blood pressure, pounding headaches, heart palpitations, facial flushing, nausea and vomiting. There is no cure for the disease, but removing the tumors before they turn cancerous can improve survival.