Analysis of claudin genes in pediatric patients with Bartter's syndrome

Missense mutation at CLDN8 associated with a high plasma interferon gamma-inducible protein 10 level in methadone-maintained patients with urine test positive for morphine

We previously reported a high plasma chemokine interferon gamma-inducible protein 10 (IP-10) level and prolonged electrocardiography QT-interval in methadone maintenance treatment (MMT) patients with HIV or HCV infection. The purpose of this study was to evaluate the genetic association of high plasma IP-10 level in the MMT patients. The gene-based and pathway-based association analyses were conducted using a genome-wide association study dataset in 344 MMT patients for identifying genes and pathways associated with plasma IP-10 level. We found that plasma IP-10 level was significantly associated with a pathway in the tight junction (P = 1.01x10-5), where the claudin 8 (CLDN8) gene had the most significant association (P = 6.8x10-5). A functional single nucleotide polymorphism (SNP) rs686364 at exon 1 of CLDN8 showed strong association with plasma IP-10 levels, in the MMT subjects with positive urine test for morphine (dominant model, P = 0.00004). The minor allele type carriers had higher plasma IP-10 levels than the major allele type carriers. Our data support that the tight junction protein claudin 8 exon 1 is a predictor for the plasma levels of IP-10 in MMT patients with urine test positive for morphine.

Tight junctions: molecular structure meets function

Tight junctions of epithelial and endothelial cells form selective barriers that regulate paracellular transport of solutes, immune cells, and drugs. Tight junctions consist of proteins that physically "seal" the tight junction but also form channels that allow for permeation between the cells, resulting in epithelial surfaces of different tightness. The tight junction proteins occludin, tricellulin, and at least 24 members of the claudin family are characterized by four transmembranal domains and two extracellular loops that, like teeth of a zipper, contact the appropriate loops from opposing cell membranes. Tight junctions are regulated in their molecular composition, ultrastructure, and function by intracellular scaffolding proteins and the cytoskeleton; such regulation serves normal, physiologic adaptation but also occurs in numerous diseases.