An abnormal gamma-aminobutyric acid B receptor composed of gamma-aminobutyric acid type B receptor 1 (GABBR1) and gamma-aminobutyric acid type B receptor 2 (GABBR2) can provoke seizures. This study was designed to assess the contribution of GABBR1 and GABBR2 in mesial temporal lobe epilepsy (MTLE). Two tag single-nucteotide polymorphisms (SNPs) of GABBR1 and four tag SNPs of GABBR2 were selected and genotyped in 318 MTLE patients and 315 non-epileptic individuals. The rs967932 A-allele of GABBR2 increased the risk of MTLE in an additive and a dominant genetic model,, respectively (P = 0.018, OR = 1.305, 95% CI 1.048-1.624 and P = 0.003, OR = 1.667, 95% CI 1.186-2.343, respectively). rs'1999501 and rs944688 of GABBR2, and rs29259 of GABBR1 were thought to be associated with MTLE; however, after a Bonferroni correction, these associations were not observed and only the rs967932 A-allele was found to increase the risk of MTLE in the dominant model (P = 0.036). The frequency at which the haplotype G-C-A-C (rs3780428-rs1999501-rs967932-rs944688) occurred in MTLE patients was significantly higher compared to the controls (12.26% vs. 6.51 %, P = 0.0004) and patients carrying this haplotype exhibited an earlier onset of MTLE (P = 0.028). No evidence of significant allelic, genotypic, or haplotypic associations were identified in the tag SNPs of the GABBR1 gene in patients with MTLE, and the polymorphism at G1465A was not observed in our samples. Our results provide the first evidence that common genetic variations in the GABBR2 gene contribute to the risk of MTLE. Moreover, the present results do not support the hypothesis that common variants of GABBR1 contribute substantially to the epileptogenic effect during MTLE in the Han Chinese. (C) 2008 Elsevier B.V. All rights reserved.