A new treatment shows promise in removing cholesterol and a discovery that flips Alzheimer’s research on its head. CLEVELAND — A single shot at preventing heart disease A single infusion. A dramatic drop in bad cholesterol. And results that may last a lifetime. An experimental gene-editing treatment is turning heads in the medical world — and researchers say it could one day change the way heart disease is prevented for millions of Americans. The treatment, published in The New England Journal of Medicinetargets a gene in the liver called PCSK9. A tiny molecular machine, wrapped in a fat coating so…