Mo. Rev. Stat. § 476.517
Any judge who is or has been a commissioner or deputy commissioner of the circuit court appointed after February 29, 1972, who has received creditable service pursuant to chapter 104, RSMo, and sections 476.515 to 476.565, based on service as a commissioner or deputy commissioner shall make a one-time retirement plan election upon application to receive retirement benefits. Such judge shall elect to receive retirement benefits based on all of the judge's service as a commissioner or deputy commissioner of the circuit court pursuant to section 104.374 or 104.1024, RSMo, or sections 476.515 to 476.565.
(L. 2001 S.B. 371)