I am looking on PubMed right now. Marked reduction in the corpus callosum has been observed in people who were abused as children (I'll try and find the paper that talks about that) and there may be some other problems with having a thin corpus callosum. With a complete absence and a probable genetic cause coupled with normal behavior, there is likely a compensation in the brain for communication between left and right hemispheres (that's my hypothesis at least.).
Corpus Callosum Volume in Railroad Workers With Chronic Exposure to Solvents.
Emotional arousal in agenesis of the corpus callosum.
Prenatal diagnosis of agenesis of corpus callosum: what is the neurodevelopmental outcome?
Corpus Callosum and Cocaine
Reduced area of the corpus callosum in posttraumatic stress disorder.
I'll stop now.