Mo. Rev. Stat. § 104.050: Years of service used in calculating annuity — noncompensated absences for illness and injury, effect — withdrawal before entitled to deferred annuity, relinquishes all rights — reinstatement of forfeited creditable service, when.

1. Years of service and twelfths of a year are to be used in calculating any annuity. Absences taken by an employee without compensation for sickness or injury of the employee of up to but not more than twelve months or for leave taken by such employee without compensation pursuant to the provisions of the Family and Medical Leave Act of 1993 shall be counted as membership service.

2. Any member who withdraws from service before he is entitled to deferred benefits under section 104.035 forfeits, waives, and relinquishes all accrued rights in the fund, including all accrued creditable service.

3. If a former employee has forfeited creditable service for any period he shall have the period of creditable service restored only upon the completion of one continuous year of service after he again becomes an employee.