Providing that the individual with Mosaic Down's syndrome has at least near normal cognitive and intellectual development, it's entirely possible to fulfill the criterion for a diagnosis of Asperger's syndrome, and the same diagnostic rule would be applicable to those with the genetic disorder known as Fragile X syndrome (mutation of the FMR1 gene within the X chromosome); however, it's quite likely that physicians may hesitate to formally diagnose a high functioning form of autism amongst individuals with DS (including the Mosaic type), presumably due to the statistical correlation of the prevalence of significant intellectual disabilities, and incidence of moderate developmental delays being extremely high within the DS population.
If the assessment was conducted by a multidisciplinary team (psychological, psychiatric, pediatric, or a combination of 2 or all three of the medical professions), there may dissentious conflict amongst the collaborative physicians to determine whether the diagnosis should be attained by the person with Down's syndrome. For example, some clinicians are so adherent to the DSM IV guidelines (adaptive behavior, speech acquisition, linguistic, and intellectual development) that may get the generalized supposition that the coexistence of DS+AS is oxymoronic, as it's construed as an extreme rarity. The upcoming merger of Asperger's syndrome, Classical autism, and high-functioning autism, into one ASD severity category, and the revoking of the language delay criterion in the DSM V may alleviate diagnostic bias, and help psychologists as-well as psychiatrists to disambiguate any uncertainties throughout an ASD assessment for well adapted, and cognitively able individuals with Down's syndrome. The prevalence of ASD's in DS is estimated at approximately 7%, making it fairly more common than in the general population not living with DS.
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Diagnosed with "Classical" Asperger's syndrome in 1998 (Clinical psychologist).
Alexithymia Questionnaire Score: 158/185
Ritvo Autism Asperger Diagnostic Scale-Revised (RAADS-R): 231/240
Aspie score: 186 out of 200
Neurotypical (non-autistic) score: 12 out of 200
AQ: 48/50 EQ: 9/80