I mentioned epilsepy in my essay and again in the additional information section (it impacted my attendance during my junior year). It was also mentioned by my GC and possibly in one of my letters of recommendation. So far I’ve received very positive results from the colleges I’ve applied to and one college began my acceptance letter by praising my tenacity as I overcame illness. So no I don’t think it will negatively impact your son’s chances.
Best of luck to your son and you in the transition to college!