Our present data, by demonstrating that Abcg4 can efflux Aβ through the mouse BBB, provides an explanation for the observation that 3-months’ aged 3xTg-AD mice could efflux more Aβ than WT, off-setting the increased RAGE-mediated influx of Aβ observed at the same time in 3xTg-AD mice51, in the face on an unchanged Clup of [3H]Aβ1–40 compared with WT mice51. The gene discussed is ABCG4; the disease is Alzheimer disease.