A Comparison of Asperger's Disorder and High Functioning Autism: Are Diagnostic Boundaries Meaningful/Useful?

Background:

The use of accurate and appropriate subtypes of pervasive developmental disorders is necessary across scientific, clinical, and educational settings. Since the inclusion of Asperger Syndrome (AS) as a diagnostic entity, a number of studies have examined the clinical presentation of AS relative to Autistic Disorder with cognitive abilities in the average range (HFA). While several studies have identified differences between AS and HFA in a variety of domains (perinatal factors, cognitive profiles, motor ability, etc), the validity of the current diagnostic subtypes remains under debate.

Objectives:

The purpose of the current study is to compare the diagnostic subtypes of AS and HFA using parent report of behavioral symptoms and neurophysiological measures of social information processing. 

Methods:

In a sample of children with continued ongoing recruitment (aged 6-18 years; mean = 10.6 years; all males) and a sample of adults (mean age = 22.3 years; all males), meeting ASD criteria on the ADI and ADOS and having a full scale IQ in the normal range, individuals were identified as AS (children: N=13; adults: N=15) or HFA (children: N=20; adults: N=13) using strict DSM-IV criteria by an experienced clinician. In the sample of children, parent report of behavior and functioning (CBCL competency scales and vineland) was examined to examine differences between diagnostic groups. In the sample of adults, EEGs were collected in response to pictures of faces and houses and in response to pictures of familiar and novel faces. To examine differences between diagnostic groups, latency and amplitude of EEG response was assessed.

Results:

In the sample of children, significant differences were found on verbal IQ between groups with the AS group performing significantly better (p<.01) than the AD group. No differences were found in the non-verbal domain. After controlling for verbal IQ, significant differences were found between groups on the school problems subscale of the CBCL with the AS group performing in the typical range and the AD group performing in the clinical range (p<.05). No differences were found between the AS and AD groups on the social and activities subscale of the CBCL competency items or Vineland scores. In the sample of adults, no differences were found on verbal and nonverbal IQ. The AS group showed faster processing of both face and house stimuli in the right hemisphere and the HFAD showed faster processing in the left hemisphere (p<.05). Further, while similar latencies were noted at an early negative going ERP component in response to familiar faces, the HFAD group showed faster processing of novel faces than the AS group (p<.05).  

Conclusions:

The preliminary findings in children suggest that meaningful differences between boys with AS and AD do exist and that despite typical school functioning and enhanced verbal IQ skills in children with AS, adaptive functioning remains significantly impaired. The findings in adults suggest processing novel social information may be different for males with AS compared to HFAD and support the conclusion that meaningful differences exist between subtypes and that these differences manifest in neurophysiological responses to social stimuli.