An arrest of spermatogenesis at the level of spermatogonia and certain human neoplastic testicular diseases (e.g., seminoma and the germ cell neoplasia in situ, formerly known as carcinoma in situ) correlate with the absence or down-regulation of the gap-junction protein Connexin 43 (Cx43) [1–5]. This evidence concerns the gene GJA1 and seminoma.