Sister Sledge was a Philadelphia quartet with some fine singles (but limited success) behind them when the Chic Organization’s Nile Rodgers and Bernard Edwards took up their case. In early 1979, as Chic themselves rode high with “Le Freak” and “I Want Your Love,” We Are Family slipped into the racks. With the band’s percolating rhythm section behind them, Kathy, Debbie, Kim, and Joni Sledge leapt into the best music of their careers. “We Are Family” itself was an ode to sisterly closeness that was immediately picked up as an anthem by an ever more visible gay culture and the Pittsburgh Pirates, who rode it to a World Series championship in 1979. “He’s the Greatest Dancer,” originally slated for Chic, caught that group’s take on sex and style perfectly, while “Lost in Music” was the smartest kind of dance-floor escapism.