An eight-year-old boy had abdominal pain, fever with bloody diarrhea for 18 months. His height is 100 cm and weight is 14.5 kg. Stool culture was negative for known entero-pathogens. The sigmoidoscopy was normal. During the same period child had an episode of renal colic and passed urinary gravel. The Mantoux test was 5 x 5 mm. The most probable diagnosis is: