Study sheds light on the function of a long-mysterious PCSK9 mutation. High LDL a leading risk factor for heart disease. Many cholesterol medications lower LDL, some of them by targeting the protein PCSK9. Scientists now report on an investigation into why experiments on PCSK9 give different results in a test tube and in liver cells. What they found may explain how a mutation in PCSK9 that has long puzzled scientists leads to heart disease. Source 2z.