Many neuroimaging and autopsy studies have reported that subjects with autism have abnormalities in specific brain regions, but the findings have not always been repeated. These reports include increased head circumference, increased brain volumes and brain weight, and specific changes in brain areas. These changes may change as children grow into adults?as children, brain volumes may be abnormally large, but as they grow older, these volumes can decrease.
To understand how brain volumes change, a brain imaging study was conducted by Dr. Aylward and his colleagues at the University of Washington. Dr. Aylward measured total brain volumes from MRI scans in 67 non-mentally retarded children and adults with autism and 83 healthy volunteers, ranging in age from 8 to 46 years. Head circumference was also measured. The results of their study was recently published (Neurology 59:176-180, 2002).
Brain volumes were significantly larger for children with autism 12 years old and younger compared with normally developing children, when controlling for height. Brain volumes for individuals older than age 12 did not differ between the autism and control groups. Head circumference was increased in both younger and older groups of subjects with autism, suggesting that those subjects older than age 12 had increased brain volumes as children.
This study confirms previous findings that in subjects with autism, enlargement of the brain may be a feature of brain development during early childhood that normalizes with maturational processes.
Brain development in autism follows an abnormal pattern, with accelerated growth in early life that results in brain enlargement in childhood. Brain volume in adolescents and adults with autism is, however, normal. There appears to be due to a slight decrease in brain volume in children with autism at the same period that normal children are experiencing a slight increase.
The authors suggest that early increase in brain volume may reflect increase numbers of brain cells (neurons) or premature and accelerated growth of brain cell connections (synapses) as well as abnormal increases in other brain cell structures. Some studies have shown elevations in brain proteins in autistic newborns, proteins that are related to accelerated brain growth.
Premature accelerated brain growth occurs at a time when the symptoms and signs of autism are emerging?failure to develop language, social, and play skills. The implication is that this acceleration in growth disrupts the formation of the proper nerve cell structure supporting the normal functioning of language and social skills.
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