The Philly singer sang on some of the greatest disco tracks of all time.

Joni Sledge, a founder member of disco troupe Sister Sledge, has died aged 60. She 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.

“Yesterday, numbness fell upon our family,” said a statement on Facebook. “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.”

Sledge formed Sister Sledge with her three siblings in 1971, but the Philadelphia group struggled to break into the industry for several years until meeting Nile Rodgers and Bernard Edwards of Chic, who wrote and produced the sisters’ debut album We Are Family.

The troupe had their first major hit with ‘He’s the Greatest Dancer’ and went on to achieve worldwide success with a string of classic disco singles including 1979’s million-selling ‘We Are Family’, ‘Lost in Music’ and ‘Thinking of You’.

After sister Kathy left the group for a solo career, the trio of sisters continued to perform and record. Sledge, who is survived by her adult son, last performed with the band in October.

Nile Rodgers paid tribute to Sledge on Twitter, saying “we did something pretty amazing together.”