The neurobiology of autism: new pieces of the puzzle.
Acosta MT, Pearl PL.
Department of Neurology, Children's National Medical Center, 111 Michigan
Avenue NW, Washington, DC 20010-2970, USA. macosta@cnmc.org
The neurobiologic basis of autism is reviewed, with discussion of evidence
from genetic, magnetic resonance imaging, neuropathology, and functional
neuroimaging studies. Although autism is a behaviorally valid syndrome, it is
remarkably heterogeneous and involves multiple developmental domains as well
as a wide range of cognitive, language, and socioemotional functioning.
Although multiple etiologies are implicated, recent advances have identified
common themes in pathophysiology. Genetic factors play a primary role, based
on evidence from family studies, identification of putative genes using
genome-wide linkage analyses, and comorbidities with known genetic mutations.
The RELN gene, which codes for an extracellular protein guiding neuronal
migration, has been implicated in autism. Numerous neuropathologic changes
have been described, including macroencephaly, acceleration and then
deceleration in brain growth, increased neuronal packing and decreased cell
size in the limbic system, and decreased Purkinje cell number in the
cerebellum. Abnormalities in organization of the cortical minicolumn,
representing the fundamental subunit of vertical cortical organization, may
underlie the pathology of autism and result in altered thalamocortical
connections, cortical disinhibition, and dysfunction of the arousal-modulating
system of the brain. The role of acquired factors is speculative, with
insufficient evidence to link the measles-mumps-rubella (MMR) vaccine with
autism or to change immunization practices.
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