title: What have we learned from recent twin studies about the etiology of neurodevelopmental disorders?
abstract: OBJECTIVE
  The relative influence of genes and environment on the liability to neurodevelopmental disorders (NDDs) can be investigated using a twin design. This review highlights the results of the most recent twin studies of NDDs.
  
  
  RESULTS
  Recent twin studies have confirmed that NDDs show moderate-to-high heritability, and that from an etiological viewpoint both autism spectrum disorder (ASD) and attention deficit hyperactivity disorder (ADHD) are best regarded as the extremes on a continuous liability distribution. Both ASD and ADHD show high heritability in childhood and a substantial drop in heritability in adulthood, which is likely explained by the use of different assessment strategies in childhood versus adulthood, or by a complex mechanism of gene-by-environment interaction. NDDs show substantial comorbidity among each other, and with other mental health problems, which is partly because of a shared genetic etiology between different disorders.
  
  
  CONCLUSIONS
  The findings of twin studies implicate substantial heritability of NDDs, and warrant large-scale molecular genetic studies for such traits.
authors: Complex Trait Genetics, Departmentof Functional Genomics, VU University Amsterdam, De Boelelaan 1085, Amsterdam,The Netherlands. d.posthuma@vu.nl
authors: Danielle
authors: D
authors: Posthuma
authors: Tinca J C
authors: TJ
authors: Polderman
mesh_terms: D001289:Attention Deficit Disorder with Hyperactivity / Q000453:epidemiology / Q000209:etiology / Q000235:genetics*; D002648:Child; D002659:Child Development Disorders, Pervasive / Q000453:epidemiology / Q000209:etiology / Q000235:genetics*; D015897:Comorbidity; D059647:Gene-Environment Interaction; D006801:Humans; D001523:Mental Disorders / Q000453:epidemiology / Q000209:etiology / Q000235:genetics*; D018433:Twin Studies as Topic