<s>[INST] <<SYS>> This is a medical question of type : causes <</SYS>> What causes Prune belly syndrome ? [/INST] What causes prune belly syndrome? The underlying cause of prune belly syndrome is unknown. The condition may occur if there is a blockage preventing the flow of urine through the urinary tract. The blockage can cause the urine to flow back into the bladder, enlarging it. </s>