Genetic Syndromes and Developmental Risk for Autism Spectrum and Attention Deficit Hyperactivity Disorders: Insights From Fragile X Syndrome

Many genetic markers are associated with atypical developmental outcomes. In this article, we review evidence from studies on the most common inherited cause of intellectual disability, fragile X syndrome ( FXS ). We aim to highlight general developmental consequences as well as specific implications for autism spectrum disorder ( ASD ) and attention deficit hyperactivity disorder ( ADHD ), including the complexity of characterizing ASD and ADHD symptoms in FXS . We address three issues: First, links among genes, brain, and cognition need to be situated in a developmental context, even in a monogenic disorder like FXS . Second, the comparatively early age of diagnosis of FXS offers the opportunity to study developmental trajectories of risk and resilience for a complex, behaviorally defined disorder highly associated with FXS but diagnosed later: ASD . Third, the high occurrence of both ASD and ADHD in FXS allows for a novel investigation of their comorbidity, with important caveats.