I don't think this is an April Fools' Joke. Perhaps they could call it Yosemite Sam Syndrome:
Disease underlies Hatfield-McCoy feud
By MARILYNN MARCHIONE, AP Medical Writer
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....
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....
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.
Her adoptive father, James Reynolds, said of the McCoys: "It don't take much to set them off. They've got a pretty good temper...
Still, many are dubious that this condition had much of a role in the bitter feud with the Hatfields, which played out in the hill country of eastern Kentucky and West Virginia for decades.
Some say the feud dates to Civil War days, when some members of the families took opposite sides. It grew into disputes over timber rights and land in the 1870s, and gained more notoriety in 1878, when Randolph or "Old Randal" McCoy accused a Hatfield of stealing one of his pigs. The hostilities left at least a dozen dead. ...
"The McCoy temperament is legendary. Whether or not we can blame it on genes, I don't know," said Randy McCoy, 43, of Durham, N.C., one of the organizers of the annual Hatfield-McCoy reunion. "There are a lot of underpinnings that are probably a more legitimate source of conflict."
"There was a lot of inter-marrying" that could have played havoc with the gene pool, he conceded. ...
Altina Waller, a professor of history at the University of Connecticut and author of a book about the feud, agreed.
"Medical folks like to find these kinds of explanations. Like the Salem witchcraft thing. That book came out about how that was caused by wheat that was grown that had this parasite or mold or fungus or something that caused everybody in Salem to go nuts," she said.
"How does it explain the other dozen or so feuds that I've looked at in other places?" she asked, citing disputes over coal and other issues. "The rage and violence as such was not confined to McCoys."
It sounds like a combination of the genetic and social effects of cousin marriage: bad recessive genes and excessive extended family loyalty, respectively. Update - Greg Cochran says it's a dominant genetic disease, not a recessive one.