A 6 yrs old boy is having recurrent apthous ulcer. He also has episodes of high grade fever associated with  pain abdomen. No organomegaly, no lymphadenopathy.

All the investigations like CBC, Typhidot, ps for mp, urine, usg abdomen is normal. Bowel habits are more or less normal. Earlier he used to have few episode of loose stools.poor weight gain What could be the cause of recurrent apthous ulcer with fever a/c pain abdomen?