Early-onset IBD, possibly due to inheritance of a greater number of susceptibility genes and/or earlier exposure to environmental triggers, differs from that occurring in adults. In children, inflammation occurs most commonly in the colon complicating differentiation between CD and UC. Early-onset CD is more common in boys (whereas adult-onset disease occurs more commonly in females) and tends to be more extensive with greater involvement of the upper intestine. Colonic inflammation in children with UC also tends to be more extensive than in adults.