Alzheimer's patients have buildups of insoluble "plaques" in the brain, which mostly consist of proteins formed by APP. "We showed that if you take away presenilin-1 you can get rid of the amyloid peptides," said Bart De Strooper, of the Flemish Institute of Biotechnology in Belgium.
Mr De Strooper and Paul Saftig of the University of Goettingen in Germany discovered the link between the two genes by breeding transgenic mice without PS1. Mice lacking PS1 usually die before birth, but the researchers used embryonic nerve cells to study how the genes react.
The work is published today in Nature. PS1 has an important role in embryo development - which is why mice without it die before birth - but might have no useful function in adults. Drug treatments which suppressed it in adults might therefore be useful.