Contents

18 November 2009
Vol 1, Issue 7

About The Cover

Cover image expansion

ONLINE COVER Three copies of human chromosome 21. People that carry an extra copy of chromosome 21 have Down syndrome, a disorder characterized by learning and cognitive difficulties, among other symptoms. Mice with a similar genetic abnormality also have learning difficulties and, as shown by Salehi et al., degeneration in a brain nucleus that uses norepinephrine as a neurotransmitter. Restoration of neurotransmitter concentrations can also restore the learning difficulties, suggesting that a similar approach in individuals with Down syndrome may prove therapeutically useful. [CREDIT: C. BICKEL/AAAS]