1. ¹Department of Psychiatry, Hospital Universitari Vall d'Hebron, Barcelona, Catalonia, Spain
2. ²Department of Psychiatry and Legal Medicine, Universitat Autónoma de Barcelona, Barcelona, Catalonia, Spain
3. ³Child and Adolescent Mental Health Unit, Department of Psychiatry, Hospital Mútua de Terrassa, Barcelona, Catalonia, Spain
4. ⁴Unitat de Neuropediatria, Hospital de Sabadell, Corporació Sanitària Parc Taulí, Barcelona, Catalonia, Spain
5. ⁵Genes and Disease Program, Center for Genomic Regulation (CRG), UPF, Barcelona, Catalonia, Spain
6. ⁶Centro Nacional de Genotipado (CeGen), Barcelona, Catalonia, Spain
7. ⁷CIBER Epidemiología y Salud Pública, Instituto de Salud Carlos III (CRG), Barcelona, Catalonia, Spain
8. ⁸Departament de Genètica, Facultat de Biologia, Universitat de Barcelona, Barcelona, Catalonia, Spain
9. ⁹CIBER Enfermedades Raras, Instituto de Salud Carlos III, Barcelona, Catalonia, Spain
10. ¹⁰Institut de Biomedicina de la Universitat de Barcelona (IBUB), Barcelona, Catalonia, Spain

Correspondence: Dr M Bayés, Genes and Disease Program, Center for Genomic Regulation (CRG), Dr Aiguader 88, Barcelona, 8003, Spain. E-mail: monica.bayes@crg.es

¹¹These authors contributed equally to this work.

Received 21 March 2007; Revised 14 June 2007; Accepted 25 July 2007; Published online 16 October 2007.

Abstract

Attention-deficit/hyperactivity disorder (ADHD) is a common psychiatric disorder in which different genetic and environmental susceptibility factors are involved. Several lines of evidence support the view that at least 30% of ADHD patients diagnosed in childhood continue to suffer the disorder during adulthood and that genetic risk factors may play an essential role in the persistence of the disorder throughout lifespan. Genetic, biochemical and pharmacological studies support the idea that the serotonin system participates in the etiology of ADHD. Based on these data, we aimed to analyze single nucleotide polymorphisms across 19 genes involved in the serotoninergic neurotransmission in a clinical sample of 451 ADHD patients (188 adults and 263 children) and 400 controls using a population-based association study. Several significant associations were found after correcting for multiple testing: (1) the DDC gene was strongly associated with both adulthood (P=0.00053; odds ratio (OR)=2.17) and childhood ADHD (P=0.0017; OR=1.90); (2) the MAOB gene was found specifically associated in the adult ADHD sample (P=0.0029; OR=1.90) and (3) the 5HT2A gene showed evidence of association only with the combined ADHD subtype both in adults (P=0.0036; OR=1.63) and children (P=0.0084; OR=1.49). Our data support the contribution of the serotoninergic system in the genetic predisposition to ADHD, identifying common childhood and adulthood ADHD susceptibility factors, associations that are specific to ADHD subtypes and one variant potentially involved in the continuity of the disorder throughout lifespan.