No causal role for the G482T and G689T polymorphisms in translation regulation of serotonin transporter (SLC6A4) or association with attention-deficit-hyperactivity disorder (ADHD)

Abstract

Purpose of the study: The G482T and G689T polymorphisms in the 3'-UTR of serotonin transporter (SLC6A4) are implicated in translational regulation and allelic variants may mediate susceptibility to attention-deficit-hyperactivity disorder (ADHD). Accordingly, we examined influence of allelic variation on stable secondary structure formation and on seed sequences necessary for microRNA-binding. Furthermore, 90 ADHD cases from India were genotyped for these markers and tested for association with ADHD.

Methods: The Mfold software was used for secondary structure predictions and miRNA-binding sequences were obtained from the PicTar database. Using a family-based study design we assessed genetic association by means of the haplotype-based haplotype relative risk (HHRR) and transmission disequilibrium test (TDT) statistics. With respect to G689T, previously published TDT data were included in pooled analysis.

Result: Secondary structure analysis reveals that G482, U482, G689 and U689 conformers are energetically similar. Unlike G482, the U482 change maps within a loop and this conformer differs in free energy by approximately 4.4kcal/mol. While G482T is proximal to various miRNA-binding sequences, it is not part of the seed sequence for any of them. Thus, G482T and G689T polymorphisms do not regulate SLC6A4 translation in cis. From the HHRR (chi(2)=0.860, p=0.353; R.R.=1.11; 95% C.I.=0.89-1.65 for G482T; chi(2)=0.902, p=0.342; R.R.=1.17; 95% C.I.=0.83-1.32 for G689T), TDT (chi(2)=1.33, p=0.25; O.R.=1.35; 95% C.I.=0.94-1.94 for G482T; chi(2)=1.45, p=0.23; O.R.=1.44; 95% C.I.=0.94-2.22 for G689T) and pooled TDT (chi(2)=0.52, p=0.47; O.R.=1.05; 95% C.I.=0.96-1.15) statistics we infer that these polymorphisms are not associated with risk of ADHD.