Autism spectrum disorder (ASD) and fetal alcohol spectrum disorders (FASD) may share characteristics, such as strong sensory interests and aversions, cognitive delays, and deficits in executive functioning and adaptive skills. [Bishop: 2007] The patterns of symptom expression, however, are more unique to each disorder.
Children with ASD and FASD both struggle in social interactions, but in different ways. While children with ASD often appear aloof and uninterested in social interactions, children with FASD tend to not only be interested in social interactions, but also indiscriminately friendly with poor boundaries and no sense of “stranger danger” (a pattern seen in the disinhibited social engagement disorder subtype of reactive attachment disorder). Furthermore, when children with FASD do approach others or engage socially, they often lack the interpersonal skills necessary to move the interaction forward in a positive way. Such behaviors might include inappropriate statements or questions; difficulties with compromising, cooperating or taking different roles with other children; difficulty with sharing; and hyperactive or impulsive behavior that is difficult to manage from the standpoint of their interaction partner. Children with FASD struggle with social cues and often misunderstand or misinterpret facial expressions and eye gazes from other people. They also tend not to understand information conveyed by speech prosody. [Stevens: 2013]
Children with FASD were better able to use gestures and nonverbal communication to interact; demonstrate empathy and sharing enjoyment in social overtures; use a greater range of facial expressions during social interactions when compared with ASD children who demonstrated a characteristically restricted pattern of use of facial expressions and gestures to communicate emotions. Thus, “shared affect behaviors” were relatively less impaired in FASD children when compared with ASD counterparts.

ASD and FASD also differ in their characteristic patterns of cognitive disability. One study comparing ASD with FASD children found that 79% of ASD children had a higher nonverbal than verbal IQ. The opposite was true for children with FASDs, with the majority demonstrating a higher verbal than nonverbal IQ.

Finally, it is important to note that an FASD diagnosis does not preclude a diagnosis of ASD, if the child in question meets criteria for both disorders. For this small minority of children, treatment will be more complex due to the need to address (sometimes overlapping) problems with behavior and social interactions associated with both disorders.