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."
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