ebook_ADHD2019

6 Rohde, Buitelaar, Gerlach & Faraone thousands) can affect the risk for the disorder. When the ADHD polygenes were analyzed as a single set of genes, Demontis et al. 10 found that the marker SNPs mostly implicated regions of the genome known to have biological significance along with regulatory elements specific to the central nervous system. Each of the polygene variants has a very small effect so many are needed to develop ADHD. This means that everyone carries some ADHD-associated DNA variants but only a few people have enough to be affected with ADHD. You may recall from our dis- cussion of twin studies that ADHD’s heritability is 74%. The GWAS data allowed computation of the heritability due to the SNPs forming ADHD’s polygenic archi- tecture. It was 22%. This indicates that polygenes account for about one-third of ADHD’s heritability. Discovery of the polygenic risk for ADHD provides a useful tool for studying the genetic overlap between ADHD and other disorders and traits. For example, several population studies have computed ADHD genetic risk scores in youth that were also measured for ADHD symptoms. These studies show that children with a higher genetic risk for ADHD have more ADHD symptoms. This finding confirms the conclusion of twin studies that the genetic susceptibility to ADHD would be a continuously varying trait in the population leading to a wide range of symptom expression. See Faraone and Larsson, 4 for details. In addition to ADHD symptoms, Demontis et al. 10 correlated ADHD’s poly- genic risk with 220 disorders and traits. That work, along with other studies, have confirmed reports from family and twin studies suggesting that ADHD shares ge- netic risk with conduct disorder, major depression and bipolar disorder. Thus, the pervasive psychiatric comorbidity observed in ADHD patients is due, at least in part, to sharing the genetic risk factors comprising ADHD’s genetic risk score. In addition to these expected associations, Demontis et al. 10 also found that the genetic risk for ADHD was correlated with the genetic risk for other traits. Posi- tive correlations were observed for obesity and smoking and negative correlations were observed for years of education, college completion, intelligence quotient and subjective well-being. These correlations are consistent with what we have learned from clinical studies of ADHD. Several novel correlations also emerged. Link in this https://www.youtube.com/ watch?v=sfHDoD01eqc