CLDN1 and Familial prostate cancer: In a study exploring the connection between abnormal expressions of claudin-1, claudin-3, claudin-4, and claudin-7 and prognostic factors in prostate cancer, Sheehan et al. determined that, like claudin-1, reduced claudin-7 expression correlated with poorly differentiated histological tumors (Sheehan et al., 2007).