When Umesh Khot attended medical school in the early 1990s, his instructors taught him and his fellow students the four warning signs of heart disease: high blood pressure, elevated cholesterol, diabetes, and cigarette use. Large studies in the 1960s and 1970s, such as the well-known Framingham Heart Study, had established these links. However, the instructors informed the students of "the 50-percent rule."
That notion, recited in classes at many medical schools and repeated in the pages of medical journals, holds that half of all people who develop heart disease won't have any of these four warning signs in their medical charts. In other words, a lot of patients whom the young doctors would be treating for heart attacks would be the victims of some unknown, probably genetic, factor.
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