title: Tryptophan hydroxylase 2 (TPH2) gene variants associated with ADHD.
abstract: Genetic and pharmacological studies have emphasised the role of serotonin 5-hydroxytryptamine (5-HT) as a possible etiologic factor in the development of attention-deficit hyperactivity disorder (ADHD). Tryptophan hydroxylase (TPH) is a rate-limiting enzyme in the biosynthesis of serotonin from tryptophan. Originally, the TPH gene was thought to be widely expressed, but a second form of TPH, TPH2, was recently identified and the TPH2 gene was found to be solely expressed in the brain. We examined eight single nucleotide polymorphisms (SNP) in the TPH2 gene for association with ADHD in 179 Irish nuclear families. Transmission disequilibrium test analysis revealed significant association between the T allele of marker rs1843809 with the disorder (chi2=12.2, P=0.0006, OR=2.36). Stratifying data by the sex of the transmitting parent showed that this association was enhanced when paternal transmission was considered (OR=3.7). In addition, several haplotypes (all including the associated marker) were associated with ADHD. These preliminary findings suggest that TPH2 is a susceptibility locus for ADHD. Further confirmation, preferably from different ethnic groups, is required to firmly implicate TPH2 in the pathophysiology of ADHD.
authors.affiliation: Department of Genetics, Trinity College Dublin, Dublin, Ireland.
authors.forename: K
authors.initials: K
authors.lastname: Sheehan
authors.forename: N
authors.initials: N
authors.lastname: Lowe
authors.forename: A
authors.initials: A
authors.lastname: Kirley
authors.forename: C
authors.initials: C
authors.lastname: Mullins
authors.forename: M
authors.initials: M
authors.lastname: Fitzgerald
authors.forename: M
authors.initials: M
authors.lastname: Gill
authors.forename: Z
authors.initials: Z
authors.lastname: Hawi
mesh_terms: D001289:Attention Deficit Disorder with Hyperactivity / Q000201:enzymology / Q000235:genetics*; D001483:Base Sequence; D017931:DNA Primers; D005260:Female; D005787:Gene Frequency; D005819:Genetic Markers; D014644:Genetic Variation; D006801:Humans; D007438:Introns; D007494:Ireland; D008297:Male; D009679:Nuclear Family; D010334:Paternity; D020641:Polymorphism, Single Nucleotide; D014365:Tryptophan Hydroxylase / Q000235:genetics*
chemical_list: D017931:DNA Primers; D005819:Genetic Markers; C494784:TPH2 protein, human; D014365:Tryptophan Hydroxylase