Mo. Rev. Stat. § 452.800: Modification of another court's determination.

Except as otherwise provided in section 452.755, a court of this state may not modify a child custody determination made by a court of another state unless a court of this state has jurisdiction to make an initial determination under subdivision (1) or (2) of subsection 1 of section 452.740 and:

(1) The court of the other state determines that it no longer has exclusive, continuing jurisdiction under section 452.745 or that a court of this state would be a more convenient forum under section 452.770; or

(2) A court of this state or a court of the other state determines that neither child, nor a parent, nor any person acting as a parent presently resides in the other state.