Vesicoureteral reflux can develop in two types, primary and secondary: Primary vesicoureteral reflux. Children with primary vesicoureteral reflux are born with a defect in the valve that normally prevents urine from flowing backward from the bladder into the ureters. Primary vesicoureteral reflux is the more common type.
https://www.mayoclinic.org/diseases-conditions/vesicoureteral-reflux/symptoms-causes/syc-20378819

