Joni Sledge, a founding member of the R&B vocal group Sister Sledge, was found dead Friday in her home in Phoenix, publicist Biff Warren told CNN on Saturday. She was 60 years old.

The Sledge family was shocked by her death as she had not been ill, Warren said. The cause of death was unknown.

The group of sisters were best known for the 1979 dance anthem "We Are Family." Other hits were "He's the Greatest Dancer" and "My Guy."

"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. Please pray for us as we weep for this loss. We do know that she is now eternally with Our Lord," the band said Saturday in a statement posted on their website and Facebook page.

Joni Sledge was born in 1957 in Philadelphia, according to the Internet Movie Database. She came from a musical family and her parents were entrepreneur/actress Florez Sledge and Broadway performer Edwin Sledge, the official Sister Sledge website says.

The sisters Joni, Debbie and Kim made up Sister Sledge. Kathy, a fourth sister, was another original member but left the ensemble in 1989, according to the group's website.

The group became famous in 1979 with the Grammy-nominated "We Are Family," written by Bernard Edwards and Nile Rodgers of Chic. The song celebrated familial bonds, became a staple at weddings and was adopted as an unofficial anthem by the Pittsburgh Pirates during their 1979 championship season.

"We Are Family" peaked at No. 2 on the Hot 100 and topped the R&B and disco charts, Billboard said. The album of the same name reached No. 3 on the Billboard 200.

A younger generation became familiar with the group's song, "He's the Greatest Dancer," when it was famously sampled in Will Smith's 1998 hit "Gettin' Jiggy Wit It."

Though their hit-making days were behind them, Sister Sledge remained active. Their next show had been scheduled for March 18 and a series of European performances was planned.