On the role of Nature and Nurture in psychiatric traits.
The ‘Psychiatric Etiology’ group studies the role of nature and nurture, including their interaction, in psychiatric traits. ‘Why do certain individuals develop a disorder, and others not?’ Is it nature or nurture, or a combination of both?
Nature or Nurture
The ‘Psychiatric Etiology’ group studies the role of nature and nurture, including their interaction, in psychiatric traits. ‘Why do certain individuals develop a disorder, and others not?’ Is it nature or nurture, or a combination of both? My main focus has been on the etiology of Attention Deficit/Hyperactivity Disorder (ADHD), and the co-occurrence with other psychiatric traits, such as Autism Spectrum Disorders (ASD) and aggression. Recently I extended my heritability studies on ADHD to a huge heritability study on all human traits that was published in ‘Nature Genetics’.
Heterogeneity of psychiatric traits
Like most psychiatric disorders, ADHD is characterized by a heterogeneous manifestation of problems such as inattention, hyperactivity and impulsivity. This heterogeneity is predominantly neglected, blurring the window to causal factors. More homogeneous phenotypes might be obtained by investigating dimensions of disorders. Evidence for dimension specific etiological factors comes from twin studies on ADHD that reported etiological overlap but also specificity for the three core dimensions inattention, hyperactivity and impulsivity. Moreover, several of my studies pointed to dimension specific associations between for instance ADHD and ASD, signifying the importance of the dimension specific approach.
Where are the genes?
Numerous studies have shown that genetic variation (nature) explains a large part of the variation in ADHD symptoms, and other psychiatric traits. The identification of genes related to psychiatric traits has been proven to be difficult. Apart from a focus on more homogeneous manifestations of problems, new gene finding strategies are crucial as well. One way to elucidate genetic pathways is to focus on functional gene networks, instead of single genes or genetic variants. In addition, the parallel investigation of brain measures and genetic information (‘imaging genetics’) in relation to psychiatric traits is a promising approach.
Gene by environment interaction
Apart from genetic effects alone, the interaction with environmental factors likely plays a role as well. Environmental risk factors that have been suggested for ADHD, ASD and aggression are in utero exposure to nicotine, alcohol, and medical drugs. We aim to investigate the role of potential environmental risks on ADHD and aggression while controlling for genetic risk, using recently available polygenic risk scores for ADHD and other psychiatric traits.
*Tielbeek JJ, Karlsson Linnér R, Beers K, Popma A, Posthuma D, Polderman TJC (2016). Meta-analysis of the Serotonin Transporter Promoter Variant (5-HTTLPR) in relation to adverse environment and antisocial behavior. American Journal of Medical Genetics Part B: Neuropsychiatric Genetics, e-pub
*Polderman TJC, Benyamin B, De Leeuw CA, Sullivan PF, van Bochoven A, Visscher PM & Posthuma D (2015). Meta-analysis of the heritability of human traits based on fifty years of twin studies. Nature Genetics, May 2015, doi:10.1038/ng.3285
* Polderman TJC, Hoekstra RA, Posthuma D & Larsson H (2014). The co-occurrence of autistic and ADHD dimensions in adults: an etiological study in 17 779 twins. Translational Psychiatry, doi: 10.1038/tp.2014.84