Mo. Rev. Stat. § 404.430

The incapacitation of a beneficiary who has transferred property to a personal custodian does not terminate the personal custodianship, directions given by the beneficiary to the personal custodian, the designation of a successor personal custodian, any of the powers or authorities of the personal custodian or the immunities of third persons acting on directions of the personal custodian. When a beneficiary becomes incapacitated, the personal custodian shall hold and administer the custodial property in accordance with the provisions of sections 404.400 to 404.650 applicable to incapacitated beneficiaries and the provisions of any written agreement between the beneficiary and the personal custodian.