TTR and Alzheimer disease: Since the evidence indicates that TTR can bind many forms of Aβ it is also possible that TTR exerts its salutary effect on AD, particularly when it is over-expressed in the APP23 mice, by enhancing the hypothesized "plasma sink" by which Aβ-binding molecules in the circulation shift the equilibrium of newly generated Aβ from the brain, where the aggregates may be cytotoxic to the peripheral circulation, where they can be degraded.