CLDN1 and diffuse astrocytoma: Karnati et al. observed a significant reduction in CLDN1 expression in glioblastoma (grade 4) and anaplastic astrocytoma (grade 3) tumor samples, compared to pilocytic astrocytoma (grade 1) and diffuse astrocytoma (grade 2) samples, in which CLDN1 expression was elevated (33).