Increased brain size in autism--what it will take to solve a mystery.

摘要

The past decade has witnessed an explosion of research into the neurodevelopmental origins of autism spectrum disorders (ASD). Magnetic resonance imaging (MRI) studies support the hypothesis that an increased brain size (BS) is the underlying cause of macrocephaly that develops in approximately 20% of patients with ASD within the first 2 years of life (see [1] for a review). As compared with both typically developing subjects and nonautistic individuals with mental retardation, individuals with ASD have a 5%-10% enlargement in total brain volume at 18 months-4 years of age. The increased BS was attributed to an increase in both the gray and white matter volumes (WMVs). Differences in BS and head circumference appear most robust in early childhood. Whether the brain enlargement persists in ASD after age 5 is not clear, although several studies have reported a 6%-12% increase in gray matter volume (GMV) in adolescents and adults with ASD (see [1] for a review). Although there are many unanswered questions regarding how the neuroanatomical perturbations seen in ASD lead to the cognitive and behavioral manifestations of the disease, it is becoming increasingly clear that the altered trajectory of brain development in ASD is probably the most reliable biomarker in this disorder.