It certainly happens. I cannot advise on medication, but I would sure check out his fatty acid consumption because that seems to be related. Lots of fish and/or cod liver oil. Fresh air and sunlight. I forget the situation, but if father is in the picture, and is non-abusive, not perfect, just non-abusive, I would look at increasing his time with his father...sometimes one on one and sometimes with his brother. Some kids, boys seem to be especially hit hard, really really need fathers....if he and his brother are very competitive or one picks on the other I would look at separate classrooms and/or afterschool activities...although for a single parent that would be quite difficult.