Los Angeles, March 12 (IANS) Joni Sledge, the singer best known for the disco anthem "We are family", has died. She was 60.Sledge, who formed Sister Sledge with her three siblings in 1971, was found unresponsive by a friend at her home in Phoenix, Arizona, her publicist said.She had not been ill and the cause of death is unknown, reports bbc.com. Sledge, who is survived by her adult son, last performed with the band in October.Her death was announced on social media on Saturday -- a week before the group were due to perform in Los Angeles.A statement released on Facebook read: "Yesterday, numbness fell upon our family. We are saddened to inform you that our dear sister, mother, aunt, niece and cousin, Joni passed away yesterday. We miss her and hurt for her presence, her radiance, and the sincerity with which she loved and embraced life."Aside from the Grammy-nominated "We are family", the hit which sold more than a million copies after it was released in 1978, the group also was known for "He's the greatest dancer", "Lost in the music" and a cover of the Motown classic "My guy".