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OBJECTIVES: Three studies to date have found evidence (or a trend for evidence) of linkage and association between the long allele of the 44 base pair repeat insertion/deletion 5-HTT functional polymorphism (5-HTTLPR) and attention deficit hyperactivity disorder (ADHD). In an attempt to replicate these findings, we examined this polymorphism and a variable number tandem repeat in the second intron of 5-HTT for association with ADHD. METHODS: One hundred and fifty children who met diagnostic criteria for ADHD and their parents (where available) were genotyped for these polymorphisms. Analysis was undertaken using the transmission disequilibrium test and haplotype analysis, as well as case-control comparisons using a control group of 121 individuals. RESULTS: No association between either the 5-HTTLPR or the variable number tandem repeat (VNTR) in ADHD was found (extended transmission disequilibrium test; P=0.37 and P=0.62, respectively). Haplotype analysis was also non-significant. Further analysis revealed no evidence of association in the subgroups of those without conduct disorder and in medication non-responders. CONCLUSIONS: Failure to replicate findings from previous studies may be due to a lack of statistical power. However, given recent findings by Kent et al. (2002) of association with another polymorphism in the 5HTT gene, we hypothesise that previous positive findings may have arisen by the LPR and VNTR being in linkage disequilibrium with the true susceptibility polymorphism.

OBJECTIVES: There has been a recent resurgence in interest in the role of autoimmunity in childhood neuropsychiatric disorders. Significant association between HLA-DRB1 and attention deficit hyperactivity disorder (ADHD) in a case-control study of 31 subjects has been reported but there have been no other published studies following up these results. We attempted to replicate these findings. METHODS: In a well-characterized sample of 173 children with ADHD, using a fully automated sequence-specific oligonucleotide method for HLA genotyping, association between ADHD and HLA-DRB1 was tested for using the Transmission Disequilibrium Test and case-control analysis. RESULTS: Transmission Disequilibrium Test analysis yielded a chi-square of 10.694 with a simulated global P value of 0.1641 for the full sample, and a chi-square value of 11.307 with a simulated global P value of 0.1323 for the complete trios only. CONCLUSION: There was no evidence of association of HLA-DRB1 and ADHD.

Objectives: Psychopathy-related traits, especially those tapping the 'emotional dysfunction' aspect of psychopathy that is characterized by lack of emotional responsiveness, are thought to be of genetic origin, but molecular genetic studies are yet to be undertaken. Gene variants that affect COMT, MAOA and 5HTT activity have previously been linked to antisocial behaviour. The aims of this study were to test whether these gene variants are linked to psychopathy traits in attention-deficit hyperactivity disorder (ADHD). Methods: Adolescents were followed up 5 years after an initial diagnosis of ADHD. Psychopathy trait scores were assessed [total scores and 'emotional dysfunction' (also referred to as 'affective') scores] and the MAOA 30-bp variable number of tandem repeats, SLC6A4 44-bp insertion/deletion and COMT Val158Met variants were genotyped. Results: All three gene variants were associated with 'emotional dysfunction' scores. MAOA and 5HTT variants were associated with total psychopathy scores. The results were not explained by associated conduct disorder. Conclusion: The results suggest that specific gene variants influence psychopathy traits in ADHD.