The regulation of Sox9 expression requires the intervention of two additional testis-determining genes: Sry and Fgf9. Recent data in the mouse have demonstrated a cell autonomous role for SRY in the upregulation of Sox9 transcription by binding to its gonadal ridge enhancer, TESCO.7,18 However, analysis of human TESCO sequences in 66 cases of 46,XY gonadal dysgenesis (GD; Swyer syndrome) revealed no mutations in two cohorts, suggesting that TESCO mutations are not a common cause of 46,XY GD in humans.54 In mouse, SRY cooperates with NR5A1 in binding to TESCO. This evidence concerns the gene SOX9 and gonadal dysgenesis.