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Novel and functional norepinephrine transporter protein variants identified in attention-deficit hyperactivity disorder.

ABSTRACT: Attention-deficit hyperactivity disorder (ADHD) is a highly heritable disorder of impaired behavioral inhibition, increased motor activity, and inattention. The norepinephrine transporter (NET, SLC6A2) represents an important candidate gene for contribution to ADHD because it regulates catecholamine extracellular and tissue concentrations and contributes to executive functions disrupted in ADHD, and NET is a target for most effective ADHD therapeutics. We identified four NET coding single nucleotide polymorphisms (SNPs) in two ADHD sample sets; two SNPs produce protein variants (T283M, V245I), one of which, T283M, is a novel variant. Examination of the maternal family members through whom the T283M mutation was transmitted, provided no additional ADHD diagnoses. Given the previous identification of a NET mutation that contributes to a familial tachycardia syndrome, we examined autonomic function to reveal in the proband the highest standing-induced increase in heart rate among the ADHD subjects examined. We measured [3H]NE and [3H]dopamine transport for T283M, V245I, and a previously identified NET variant, T283R. T283M and V245I demonstrated decreased substrate transport, as did T283R, suggesting that the T283 residue is sensitive to mutation. Identification of polymorphic sites within NET, specifically those that produce functional consequences, is one critical step in elucidating the genetic variation contributing to the heritable component of diseases such as ADHD.

SUBMITTER: Hahn MK

PROVIDER: S-EPMC2801604 | biostudies-literature | 2009 Dec

REPOSITORIES: biostudies-literature

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Novel and functional norepinephrine transporter protein variants identified in attention-deficit hyperactivity disorder.

Hahn Maureen K MK Steele Angela A Couch R Steven RS Stein Mark A MA Krueger Jessica J JJ

Neuropharmacology 20090819 7-8

Attention-deficit hyperactivity disorder (ADHD) is a highly heritable disorder of impaired behavioral inhibition, increased motor activity, and inattention. The norepinephrine transporter (NET, SLC6A2) represents an important candidate gene for contribution to ADHD because it regulates catecholamine extracellular and tissue concentrations and contributes to executive functions disrupted in ADHD, and NET is a target for most effective ADHD therapeutics. We identified four NET coding single nucleo ...[more]

PMID: 19698724

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Project description:Individuals with attention deficit hyperactivity disorder (ADHD) show gray matter volume (GMV) reduction in the putamen. KTN1 variants may regulate kinectin 1 expression in the putamen and influence putamen structure and function. We aim to test the hypothesis that the KTN1 variants may represent a genetic risk factor of ADHD. Two independent family-based Caucasian samples were analyzed, including 922 parent-child trios (a total of 2,757 subjects with 924 ADHD children) and 735 parent-child trios (a total of 1,383 subjects with 613 ADHD children). The association between ADHD and a total of 143 KTN1 SNPs was analyzed in the first sample, and the nominally-significant (p < .05) risk SNPs were classified into independent haplotype blocks. All SNPs, including imputed SNPs within these blocks, and haplotypes across each block, were explored for replication of associations in both samples. The potential biological functions of all risk SNPs were predicted using a series of bioinformatics analyses, their regulatory effects on the putamen volumes were tested, and the KTN1 mRNA expression was examined in three independent human putamen tissue samples. We found that fifteen SNPs were nominally associated with ADHD (p < .05) in the first sample, and three of them remained significant even after correction for multiple testing (1.3 × 10-10 ≤ p ≤ 1.2 × 10-4 ; α = 2.5 × 10-3 ). These 15 risk SNPs were located in five haplotype blocks, and 13 SNPs within four of these blocks were associated with ADHD in the second sample. Six haplotypes within these blocks were also significantly (1.2 × 10-7 ≤ p ≤ .009) associated with ADHD in these samples. These risk variants were located in disease-related transposons and/or transcription-related functional regions. Major alleles of these risk variants significantly increased putamen volumes. Finally, KTN1 mRNA was significantly expressed in putamen across three independent cohorts. We concluded that the KTN1 variants were significantly associated with ADHD. KTN1 may play a functional role in the development of ADHD.

Project description:BACKGROUND:Attention Deficit Hyperactivity Disorder (ADHD) can lead to drastic problems for the patient and its worldwide prevalence is 5%-12%. It also has many comorbidities with other disorders, and the genetic contribution seems the most significant cause. OBJECTIVES:The current study was conducted to investigate the association between norepinephrine transporter-3081 (A/T) polymorphisms and ADHD in Iranian population. PATIENTS AND METHODS:Participants were chosen from children and adolescents diagnosed with ADHD referred to Imam Hoseyn Hospital. A child and adolescent psychiatrist confirmed the diagnosis using the Kiddie-Sads-Present and Lifetime Version (K-SADS-PL) semi-structural interview. The control group was from pupils of schools in Tehran (capital city of Iran) who had no history or presence of psychiatric and medical complications. Also, a child and adolescent psychiatrist confirmed their health using the K-SADS-PL semi-structural interview. Genetic examinations were DNA distraction, Polymerase Chain Reaction (PCR), and Restricted Fragment Length Polymorphism (RFLP), which were conducted according to standard protocols. The statistical analysis was performed using chi-square and Fisher's exact test in SPSS version 21. RESULTS:The percentages of ADHD subtypes for combined, inattentive, and hyperactive/impulsive were 72.2%, 17.2%, and 11.9%, respectively. There was no significant association between norepinephrine transporter polymorphism and ADHD (P = 0.81). Moreover, no significant relationship was found between gender [male (P = 0.92) and female (P = 0.63)] and polymorphism. No significant association was found between subtypes of ADHD [combined (P = 0.46), inattentive (P = 0.41), hyperactive/impulsive (P = 0.32)] and polymorphism SCL6A2. This lack of association can also be seen in gender in every subtype. CONCLUSIONS:The results of the study show no significant association between norepinephrine transporter polymorphism SCL6A2 and ADHD.

Dataset Information

Novel and functional norepinephrine transporter protein variants identified in attention-deficit hyperactivity disorder.

Publications

Novel and functional norepinephrine transporter protein variants identified in attention-deficit hyperactivity disorder.

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