Social Processing in Autism Spectrum Disorder versus Agenesis of the Corpus Callosum

Background: Imaging studies in autism have reported a reduction in the size of the corpus callosum, suggesting it is a disorder of connectivity among brain regions, in particular between hemispheres.  An interesting group of individuals to compare with autism are those with agenesis of the corpus callosum (AgCC), where the corpus callosum has failed to develop either completely or partially in utero.  AgCC is a rare condition, with a recent estimate of 2.6 per 10,000 live births (1.8 per 10,000 for isolated AgCC unaccompanied by additional neurological abnormalities or genetic syndromes).  AgCC is associated with a wide range of behavioural and cognitive difficulties from severe to mild learning difficulties or no developmental delay.  Recent evidence suggests that even when cognitive or intellectual impairments are not obvious, subtle deficits in socio-communicative functioning may still be present.
Objectives: The aim of this study is to see whether individuals with isolated AgCC share some of the social deficits of individuals with autism spectrum disorder (ASD) due to problems in theory of mind and/or emotion processing.  The ultimate aim is to contribute to understanding the brain basis of social comprehension.
Methods: 16 individuals with partial (N = 7) or complete (N = 9) AgCC (aged 6 to 51 years; IQ 69-111) were compared on a battery of tasks assessing social understanding and emotion recognition to 16 individuals with ASD and 16 typically developing controls, matched individually for age, gender and IQ.  Where available, information was also collected from parents about participants’ social functioning and adaptive abilities.
Results: A subgroup of individuals with AgCC was found to have a cognitive profile characteristic of individuals on the autism spectrum.  However, social functioning can be intact in the absence of the corpus callosum: half the individuals with AgCC were unimpaired across tasks of emotion processing and representing the mental states of others. 
Conclusions: Individuals with AgCC present a complex picture and the social difficulties encountered in some individuals include a difficulty recognising others’ thoughts and feelings.  Further studies, including for example DTI, are needed to establish why some individuals with AgCC show ASD-like social impairments while others do not.  The present findings, however, with a sample size that is large in the study of AgCC, do suggest that even complete absence of the corpus callosum is not in itself sufficient to cause ASD.