Mo. Rev. Stat. § 461.048: Disclaimer.

If a beneficiary of a nonprobate transfer disclaims in whole or in part the nonprobate transfer in the manner provided by law, then with respect to the disclaimed transfer, the disclaimant is treated as having predeceased the owner unless the beneficiary designation provides otherwise; but the possibility that a beneficiary or descendant may disclaim a transfer shall not require any transferring entity to withhold making the transfer in the normal course of business.