Serotonin transporter gene (5-Htt): Association analysis with temporal lobe epilepsy

Abstract

Two functional polymorphisms, a 44bp insertion/deletion polymorphism in the 5' regulatory region and a variable number of tandem repeat polymorphisms in the second intron of the serotonin transporter gene (5-HTT), were previously identified and suggested to modulate transcription. The current study was designed to determine the contribution of these polymorphisms in the 5-HTT gene to susceptibility to temporal lobe epilepsy (TLE). Two hundred and seventy six patients with TLE, and 309 age- and sex-matched healthy controls from Calabria (Southern Italy) were studied. Patients and controls were genotyped using the WAVE TM DNA Fragment Analysis System for the insertion/deletion polymorphism in the promoter region (5-HTTLPR), and the GENESCAN TM System for the variable number tandem repeat (VNTR) in the second intron of the 5-HTT gene (5-HTTVNTR). The program UNPHASED was used to compare genotype, allele and haplotype frequencies between cases and controls, including age and gender as covariates in the model. No significant differences between cases and controls were observed for 5-HTTLPR, but a significant association was obtained for the 5-HTTVNTR polymorphism, both modeling genotypes (P-value=0.0145) or alleles (P-value=0.0086). Patients with TLE showed lower frequencies of the 10 repeat at 5-HTTVNTR than the controls (26.2% in patients versus 40.8% in controls). The frequency of homozygous individuals for the 10 allele was observed to be lower among patients than the controls (5.2% of patients were 10/10 versus 18.8% of controls). Haplotype analysis did not increase the evidence for association. These results suggest that the serotonin transporter gene may play a role in the etiology of TLE.