ROBO2 and hydronephrosis: To determine if these abnormally located UVJs in Robo2-deficient mice lead to VUR or urinary obstruction, we performed noninvasive echo-enhanced ultrasonic cystography with a microbubble ultrasound contrast agent (UCA) in four 6-week old Robo2 female mosaic mice that had been diagnosed with unilateral antenatal hydronephrosis and four age-matched wild-type controls.