RT Journal A1 Hoeft F, Walter E, Lightbody AA, et al T1 NEuroanatomical differences in toddler boys with fragile x syndrome and idiopathic autism JF Archives of General Psychiatry JO Archives of General Psychiatry YR 2011 FD March 7 VO 68 IS 3 SP 295 OP 305 DO 10.1001/archgenpsychiatry.2010.153 UL http://dx.doi.org/10.1001/archgenpsychiatry.2010.153 AB Currently, lists of inclusion and exclusion criteria form the basis of all DSM -based diagnoses. One prevalent developmental disorder, autism (AUT), is characterized by a suite of altered behaviors including difficulties with social interactions, impairments in language, and repetitive and restrictive interests.1 Interestingly, many individuals with fragile X syndrome (FXS), a condition arising from mutations of a specific gene on the X chromosome, also exhibit behaviors on the AUT spectrum, making FXS the most common known single-gene cause of AUT. Because of the broad similarity in behavioral phenotype, researchers have hoped that characterization of the morphological brain changes in FXS may lead to a helpful neuroanatomical model for idiopathic AUT (iAUT) as well. However, aberrant behaviors are likely the result of a complex interplay of brain changes, and the correspondence between behavior and brain change may not necessarily be one-to-one. That is, a behavior that looks similar to an outside observer may potentially be caused by any of a number of different brain states. There is still little evidence supporting the idea that the similarly aberrant behaviors exhibited by those with FXS and iAUT are the result of similar brain changes. Thus, it is possible that the behaviors exhibited by FXS and iAUT, although similar on the surface, are the result of differing morphological brain changes. Although we are operating within the framework just outlined, the utility and validity of the diagnostic taxonomy of AUT and the (dis)similarities between symptoms of AUT seen in FXS and iAUT are currently topics of active discussion.2