Abstract
BackgroundTryptophan hydroxylase-2 (TPH2) is a potential candidate gene for screening tic disorder (TD).MethodsA case–control study was performed to examine the association between the TPH2 gene and TD. The Sequenom® Mass ARRAY iPLEX GOLD System was used to genotype two single nucleotide polymorphisms (SNPs) of the TPH2 gene in 149 TD children and in 125 normal controls.ResultsFor rs4565946, individuals with the TT genotype showed a significantly higher risk of TD than those with TC plus CC genotypes [odds ratio (OR) =3.077, 95% confidence interval (CI): 1.273–7.437; P = 0.009], as did male TD children with the TT genotype (OR = 3.228, 95% CI: 1.153–9.040; P = 0.020). The G allele of rs4570625 was significantly more frequent in TD children with higher levels of tic symptoms (Yale Global Tic Severity Scale, YGTSS) than those in controls among the male children (OR = 1.684, 95%: 1.097–2.583; P = 0.017]. TD children with severe tic symptoms had significantly higher frequencies of rs4546946 TT genotype than did normal controls in boys (OR = 3.292, 95% CI: 1.139–9.513; P = 0.022). We also found that genotype distributions of both SNPs were different between the Asian and European populations.ConclusionsOur results indicated that the TT genotype of rs4565946 is a potential genetic risk factor for TD, and the allele G of rs4570625 might be associated with the severity of tic symptoms in boys. These polymorphisms might be susceptibility loci for TD in the Chinese Han population. Because of the confounding of co-existing attention deficit hyperactivity disorder (ADHD),these findings need to be confirmed by studies in much larger samples.
Highlights
Tryptophan hydroxylase-2 (TPH2) is a potential candidate gene for screening tic disorder (TD)
Genotype and allele frequencies of TPH2 polymorphisms Genotype information was successfully obtained from 274 participants (149 cases and 125 controls)
Both single nucleotide polymorphisms (SNPs) were found to be in Hardy-Weinberg equilibrium (HWE) in controls
Summary
Tryptophan hydroxylase-2 (TPH2) is a potential candidate gene for screening tic disorder (TD). Data from pharmacological studies indicate the use of serotonin reuptake inhibitors (SRIs) is effective in tic reduction in some TD children [16,17]. It was thought that there was only one gene encoding TPH, referred to as tryptophan hydroxylase isoform (TPH1). TPH knockout mice exhibited no significant differences in 5-HT-related behaviors. This observation confirmed the hypothesis of the existence of a second TPH isoform (TPH2) [19]. Several studies demonstrate that in humans TPH2 is exclusively expressed in serotonergic neurons of the brain, with the predominant expression in the Raphe nuclei of the midbrain, whereas TPH1 is mostly expressed in peripheral tissues [20]. TPH2 is located on chromosome 12q21.1; it spans a region of 93.5 kb and harbors 11 exons [20]
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