ABSTRACT
Attention deficit hyperactivity disorder (ADHD) is a highly heritable and common disorder thought to arise, in part, from alterations in dopamine function. NR4A2, or Nurr1, is an orphan nuclear receptor implicated in the development of dopaminergic cells of the ventral tegmental area (VTA) and the substantia nigra (SN). Dopaminergic cells of the VTA provide innervation to the prefrontal cortex, believed to be of major importance in the etiology of ADHD, suggesting that NR4A2 is a potential candidate gene for ADHD susceptibility. This study aimed to identify polymorphisms in NR4A2 and test their association to ADHD. Database analysis revealed a CA repeat polymorphism in the 3' UTR of NR4A2 that was confirmed by PCR. SSCP screening revealed a common DeltaC polymorphism, 254 bp 5' to the transcriptional start site. These polymorphisms were tested for an association with ADHD in both a case control study of individuals from the Milwaukee Longitudinal Study of ADHD (103 cases and 66 controls), and in 35 families composed of trios or affected sib pairs (ASP) with ADHD. Functional effects of the promoter polymorphism were tested in vitro. The non-deleted allele was significantly more active in undifferentiated SK-N-MC cells compared to differentiated SK-N-MC and HeLa cells while a trend for increased activity for the DeltaC allele was observed in undifferentiated SK-N-MC cells. Identification of these polymorphisms may aid future candidate gene studies in disorders with altered dopamine signaling, such as schizophrenia Parkinson's disease and ADHD.
Subject(s)
Attention Deficit Disorder with Hyperactivity/genetics , DNA-Binding Proteins/genetics , Polymorphism, Genetic , Transcription Factors/genetics , Base Sequence , Cell Line, Tumor , Child , Child, Preschool , DNA/chemistry , DNA/genetics , DNA Mutational Analysis , Gene Expression , Genotype , Haplotypes , HeLa Cells , Humans , Linkage Disequilibrium , Luciferases/genetics , Luciferases/metabolism , Nuclear Receptor Subfamily 4, Group A, Member 2 , Polymorphism, Single-Stranded Conformational , Promoter Regions, Genetic/genetics , RNA, Messenger/genetics , RNA, Messenger/metabolism , Recombinant Fusion Proteins/genetics , Recombinant Fusion Proteins/metabolism , Reverse Transcriptase Polymerase Chain Reaction , Sequence Homology, Nucleic Acid , TransfectionABSTRACT
Attention deficit hyperactivity disorder (ADHD) is a highly heritable and common disorder that partly reflects disturbed dopaminergic function in the brain. Recent genetic studies have shown that candidate genes involved in dopamine signaling and metabolism contribute to ADHD susceptibility. We have initiated genetic studies in a unique cohort of 158 ADHD and 81 control adult subjects who have been followed longitudinally since childhood in the Milwaukee study of ADHD. From this cohort, genetic analysis was performed in 105 Caucasian subjects with ADHD and 68 age and ethnicity-matched controls for the DRD4 exon 3 VNTR, the SLC6A3 (DAT1) 3' UTR VNTR, dopamine beta hydroxylase (DBH) TaqI A polymorphism, and the DBH GT microsatellite repeat polymorphism that has been quantitatively associated with serum levels of DBH activity, but not previously studied in ADHD. Results indicate a significant association between the DBH TaqI A1 allele and ADHD (P = 0.018) with a relative risk of 1.33. The DBH GT repeat 4 allele, which is associated with high serum levels of DBH, occurred more frequently in the ADHD group than controls, but the difference did not reach statistical significance. Associations were not found with the SLC6A3 10 repeat or DRD4 7 repeat alleles. These results indicate that the DBH TaqI A allele, or another polymorphism in linkage disequilibrium with this allele, may confer increased susceptibility towards ADHD.
