Mark is hyperactive, often flaps his arms wildly about, and will bang his head against a wall over and over for no apparent reason. he cannot relate to his peers very well and uses very bizarre language. his doctors have excluded him from a diagnosis of autism, because genetic testing revealed that damage to a chromosome can account for his symptoms. mark probably has

Fragile X Syndrome

Explanation:

According to my research on studies conducted by medical professionals, I can say that based on the information provided within the question Mark is probably suffering from Fragile X Syndrome. This is a syndrome that causes mild to severe intellectual disability, some symptoms may include delays in talking, anxiety and hyperactive behavior. Which is why it may sometimes be mistaken for Autism.

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answer; criterion validity