Attention-deficit/hyperactivity disorder (ADHD) is a highly prevalent neurodevelopmental disorder, the most common mental disorder in children. The disorder is associated with severe impairments throughout the lifespan, and with many different adverse outcomes.
Danish registers allow long prospective follow-up studies of all individuals in Denmark, without attrition. This is especially important when studying ADHD, because the disorder is associated with a high drop out in follow-up studies. Register-based studies can provide a follow-up of 100 % of the original sample, even after 30 years.
For instance, researchers at NCRR were the first to document that ADHD is associated with an increased risk of premature death. In addition, NCRR has contributed to other long-term follow-up studies, documenting that persons with ADHD have an increased risk of developing other mental disorders later in life, including substance use disorders, affective disorders, and psychosis; and also that children with ADHD have an increased risk of injuries and emergency ward visits, teenage parenthood, and criminality in adulthood.
Moreover, NCRR was first-mover in studies that included large samples of females with ADHD, providing important information on sex differences in ADHD, such as patterns of treatment, comorbidity and other characteristics and long-term prognosis. Finally, NCRR has also performed studies, investigating associations between ADHD and prenatal exposure to asthma-medication, maternal autoimmune diseases, and risk factors in early childhood, such as social adversities, febrile seizures and epilepsy.
Although the exact etiology of ADHD is still unknown, we know that both genetic and environmental risk factors are important: In a meta-analysis of 20 twin studies, the heritability of ADHD was 75 %. Currently, Denmark is probably the only place, where it is possible to perform prospective studies using nationwide cohorts, including large samples of patients with ADHD and random controls, on whom both genetic and environmental data is available.
Recently, NCRR contributed to a study identifying SNP’s in 12 loci genome-wide significantly associated with ADHD. These molecular genetic data now allow direct measurements of genetic liability of ADHD, by for instance a polygenic risk score (PRS). NCRR researchers will combine PRS for ADHD and environmental data to learn more about the etiology and outcome of ADHD.
Currently, NCRR is involved in projects that examine questions like:
For further reading:
Gundel LK, et al (2017) “Longitudinal association between mental disorders in childhood and subsequent depression - a nationwide prospective cohort study. J. Affect. Disord: https://doi.org/10.1016/j.jad.2017.10.023
Liang H, et al (2017) “In utero exposure to beta-2-adrenergic receptor agonist and attention-deficit/hyperactivity disorder in children. Eur Child Adolesc Psychiatry: https://doi.org/10.1007/s00787-017-0956-4
Demontis D, et al (2017) “Discovery Of The First Genome-Wide Significant Risk Loci For ADHD.” bioRxiv: https://doi.org/10.1101/145581
Nielsen PR, et al (2016) “Associations Between Autoimmune Diseases and Attention-Deficit/Hyperactivity Disorder: A Nationwide Study” J Am Acad Child Adolesc Psychiatry: https://doi.org/10.1016/j.jaac.2016.12.010
Riglin L, et al (2016) ”Investigating the contribution of genetic risk variants to Attention Deficit/Hyperactivity Disorder trajectories in the general population” JAMA Psych: https://doi.org/10.1001/jamapsychiatry.2016.2817
Butt JH, et al (2016) “Beta-blockers for Exams Identify Students at High Risk of Psychiatric Morbidity.” J Child Adolesc Psychopharmacol: https://doi.org/10.1089/cap.2016.0079
Bertelsen EN, et al (2016) “Childhood Epilepsy, Febrile Seizures, and Subsequent Risk of ADHD. Pediatrics: https://doi.org/10.1542/peds.2015-4654
Ottosen C, et al (2016) Gender differences in associations between attention-deficit/hyperactivity disorder and substance use disorder. J Am Acad Child Adolesc Psychiatr: https://doi.org/10.1016/j.jaac.2015.12.010
Dalsgaard S, et al (2015) “Effect of Drugs On the Risk of Injuries in Children with Attention-Deficit/Hyperactivity Disorder - A Prospective Cohort Study.” Lancet Psychiatry. https://doi.org/10.1016/S2215-0366(15)00271-0
Dalsgaard S, et al (2015). Mortality in Children, Adolescents and Adults with Attention Deficit Hyperactivity Disorder - a nationwide cohort study. Lancet Psychiatry: https://doi.org/10.1016/s0140-6736(14)61684-6