Mo. Rev. Stat. § 169.574: Members may designate trust as beneficiary.

Notwithstanding any other law to the contrary, in addition to any options available to members or retired members pursuant to this chapter, any such member or retired member may at any time designate an existing revocable or irrevocable trust or any other legal entity as the beneficiary to receive any accumulated contributions payable at the death of the member, the retired member or a beneficiary receiving monthly benefits under this chapter. Such designation shall be in writing and shall comply with rules of the board of trustees of the affected retirement system.