In the mountain villages of northwestern Colombia, an overwhelming number of people from an extended family are afflicted with Alzheimer's disease, struck in their prime by an illness known as "La Bobera," the foolishness, a condition whose origin has been attributed in hushed rumors to everything from touching a mysterious tree to the revenge of a wronged priest.   Over three centuries, many in this clan of 5,000 people have inherited a single genetic mutation that guarantees they will develop Alzheimer’s. With the help of Fransicso Lopera, a doctor in Medellin who has been studying this family lineage for more than 20 years, family members will now be able to join a study which could diagnose the disease earlier and ultimately slow the effects of the disease through drugs.  In Angostura, families gathered as the doctors announced these trials, giving them a renewed sense of hope.