This appears to be the study according to its date. It didn't give any population numbers by race. Here's an article about the earlier Russian study.
bttt
--New imaging technology suggests an experimental drug for Alzheimer's reduces clumps of plaque in the brain by around 25 percent, lifting hopes for a medicine that disappointed in clinical tests two years ago.
---Bapineuzumab being developed by Pfizer Inc, Irish drugmaker Elan Corp. and Johnson & Johnson is a potential game-changer because it could be the first drug to treat the underlying cause of the degenerative brain disease.