GJA1 and Sertoli Cell-Only Syndrome: The absence of CX43 expression in human Sertoli cells is associated with Sertoli cell-only syndrome (SCO) and impaired spermatogenesis in male patients (Brehm et al., 2002; Defamie et al., 2003), but whether the deletion of CX43 directly affects the characteristics of human Sertoli cells has not been demonstrated.