Joni Sledge of Philadelphia's 'We Are Family' group Sister Sledge has died

Joni Sledge of the Philadelphia sibling group Sister Sledge, best known for "We Are Family," the 1979 sing-along anthem of female and familial solidarity, has died. She was 60.

Ms. Sledge died of unknown causes at her home in Phoenix on Friday, according to her publicist, Biff Warren, who said she had not been ill.   

Sister Sledge was formed in 1971 with Joni, the second eldest of four siblings, together with sisters Debbie, Kim, and Kathy. They came from a family of performers: father Edwin Sledge was a tap dancer and mother Florez an actress, and they studied music with their grandmother Viola Williams, an opera singer with whom they sang at the Williams Temple Christian Methodist Episcopal Church in the Grays Ferry section of South Philadelphia as children.

Sister Sledge struggled though the '70s, scoring minor hits in Europe. "We'd been working in Atlantic City, 4 in the afternoon to 4 in the morning, six sets, opening for everybody that came through – the Emotions, Bill Withers, the Pointer Sisters," Joni Sledge told the Guardian last year. "And they were all really encouraging: 'You girls are really good, you should stick with it.' "