AQP9 and Polyhydramnios: In the present report, we describe novel phenotypes of Lrp4−/− mice and present two possible causes of polyhydramnios observed in Lrp4−/− mice: inability to swallow, which results in the disruption of a major route of amniotic fluid removal, and downregulated expression of AQP1 and AQP9, which may affect amniotic fluid clearance.