(1) A member who meets the service requirements of section 23(1)(a) but not the age requirements of section 23(1)(b), a member who does not meet the requirements of section 23(10)(b), or a deferred vested member may receive a retirement allowance if the board has received a certification by not less than 2 licensed physicians appointed by the board stating that the member or deferred vested member is disabled from engaging in any substantial gainful activity by reason of a medically determinable physical or mental impairment that can be expected to result in death, or can be expected to last for a continuous period of 12 months or more.

  (2) A member or deferred vested member who is determined eligible to receive a retirement allowance under subsection (1) shall receive the retirement allowance applicable to that member or deferred vested member provided for in section 23(4), (5), or (6).

  (3) A member who is currently receiving compensation as a legislator or lieutenant governor shall not receive a retirement allowance under this section.

  (4) The board may provide for the examination by 1 or more licensed physicians designated by the board at least once a year of a person who is receiving a retirement allowance under this section during the continuance of the disability. The board shall not provide for an examination after the member attains 55 years of age.