So your son stopped pooping his pants in 4th grade? Why? What was the defining moment or issue? Does he think that the way his parents handled worked? Apparently not, if it lasted that long.
Keep documented trail of medical appointments, tests, etc. When he goes elementary school this will be an issue with school officials and who could possibly bring DGS to the attention of Child Protective Services and DD will need to prove the DGS is not being abused or neglected.