What is CSRS discontinued service retirement?
A “discontinued service retirement” is an involuntary retirement that provides an immediate annuity to employees who are retired against their will. They have the same minimum age and service requirements as early retirement but are subject to several additional requirements or procedures. See Chapter 3, Section 5 in the Federal Employees Almanac.

CSRS retirees who retire under age 55 will have their annuities reduced by one-sixth of 1 percent for each full month they are under age 55 (2 percent per year) at retirement. The reduction is permanent. Otherwise, benefits are calculated under the same formula as for standard voluntary retirement.