Abstract
Autism spectrum disorder (ASD) is a common comorbid condition in people with fragile X syndrome (FXS). It has been assumed that ASD symptoms reflect the same underlying psychological and neurobiological impairments in both FXS and non-syndromic ASD, which has led to the claim that targeted pharmaceutical treatments that are efficacious for core symptoms of FXS are likely to be beneficial for non-syndromic ASD as well. In contrast, we present evidence from a variety of sources suggesting that there are important differences in ASD symptoms, behavioral and psychiatric correlates, and developmental trajectories between individuals with comorbid FXS and ASD and those with non-syndromic ASD. We also present evidence suggesting that social impairments may not distinguish individuals with FXS with and without ASD. Finally, we present data that demonstrate that the neurobiological substrates of the behavioral impairments, including those reflecting core ASD symptoms, are different in FXS and non-syndromic ASD. Together, these data suggest that there are clinically important differences between FXS and non-syndromic ASD that are masked by reliance on the categorical diagnosis of ASD. We argue for use of a symptom-based approach in future research, including studies designed to evaluate treatment efficacy.
Highlights
Autism spectrum disorder (ASD) is a common comorbid condition in people with fragile X syndrome (FXS)
The most important implication of the findings considered in this article is that the use of the categorical diagnosis of ASD in FXS masks important differences within the syndrome and between the syndrome and non-syndromic cases of ASD
Individuals with fragile X syndrome (FXS) who are diagnosed with Autism spectrum disorder (ASD) have less severe impairments in several of the social and communication symptoms that are diagnostic of ASD than do individuals with non-syndromic ASD, and these differences have emerged in a number of analyses and cohorts and across a variety of matching strategies
Summary
Autism spectrum disorder (ASD) is a common comorbid condition in people with fragile X syndrome (FXS). The prevalence of ASD in FXS has been estimated at 50%, there is considerable variability across studies (Demark et al, 2003; Kaufmann et al, 2004; Harris et al, 2005; Budimirovic and Kaufmann, 2011) This high rate of co-occurrence has led many researchers to suggest that FXS, being an etiologically “simpler” (i.e., a single-gene) disorder, will provide insights into the etiology of non-syndromic ASD (Belmonte and Bourgeron, 2006). We present evidence suggesting that ASD in FXS and non-syndromic ASD may differ in important ways
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