The Gamma 7A system was a solar system located in Sector 39J with billons of inhabitants until 2268.
This year, while the system was investigated by the USS Intrepid, both the system and the Intrepid were attacked by the space amoeba and all life was wiped out. As contact with the system therefore ceased, nearby Starbase 6 ordered the USS Enterprise (NCC-1701) to investigate; the ship was finally able to destroy the amoeba. (TOS: "The Immunity Syndrome")