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...