E, R Carper and N akshoomoff. 2003. Evidence of Brain Overgrowth
in the First Year of Life in Autism. JAMA
et al. present data linking autism to an unusual pattern
of brain growth shortly after birth. Infants who later develop autism
have a slightly reduced head circumference at birth, compared to
normal infants, but undergo a rapid spurt in growth during the first
two years of life. This growth spurt is so strong that by the age
of 3-4, when behavioral signs of autism are just beginning to show,
autistic children's brains are larger than normal.
authors conclude that the causes of autism must therefore lie in
factors that lead first to reduced head circumference in birth and
the subsequent the rapid spurt in brain growth, rather than factors
that are not experienced until behavioral signs of autism are evident,
such as exposure to mercury in vaccines.
did they do? Courchesne et al. compared the growth
patterns of autistic children's heads with those of normal children,
using data from two national studies as reference points. They also
compared measurements of body length and weight. The autistic children
had all participated in a study of their brains using a non-invasive
imaging technique called magnetic
This provided additional details about sizes of different parts
of the brain.
did they find? Several highly significant differences emerged
in comparing the autistic children with the reference data sets.
circumference at birth was smaller than normal, although body
weight and height were not.
at 1-2 months of age, the head circumferences of autistic children
began to grow substantially more rapidly than normal children.
6-14 months of age, autistic children's head circumferences were
substantially larger than normal children's. This persisted through
the age of 3-4 years.
graph to the right compares the relative head sizes of autistic
and normal children. It shows how much larger or smaller an
autistic child's head circumference would be than the average
size of a normal child's head at different ages.
birth, autistic children's head circumference is significantly
smaller. A rapid spurt of growth starts soon thereafter, so
that by age 6-14 months, the head circumference is significantly
levels shown for points that differ significantly from normal.
from Courchesne et al.
their MRI observations, Courchesne et al discovered that
the certain brain structures and tissues differed in relation to
head circumference and the spurt in growth of head size. For example,
smaller head circumference at birth was correlated with smaller
amounts of gray tissue in the cerebellum in childhood. Infants that
underwent rapid increases in head circumference were more likely
to have larger amounts of cerebral gray tissue. Larger head circumference
at 6-14 mo age was associated with larger amounts of cerebral gray
and white matter, whole brain gray and white matter, and whole brain
another important observation, the authors noted that children diagnosed
underwent more rapid increases in head circumference before 6-14
mo age than children diagnosed with a milder form of autism (known
to specialists as PDD-NOS).
does it mean? This study confirms that biological evidence
of autism can be found in the brains of autistic children before
behavioral indications are apparent, and the first signs are evident
at birth. According to the authors, this indicates that factors
experienced by children at the age when they begin to show behavioral
signs of autism are unlikely to be the cause of the disorder, for
example mercury in vaccines. The authors acknowledge that events/exposures
during childhood may be important as aggravating factors, but they
can't be responsible for its basic causation. The abnormally high
rates of brain growth they observed were seen in only 6% of nonautistic
cases but in 59% of autistic cases.
variation on their interpretation would be that the high rates of
brain growth from birth to 2 years of age are necessary antecedants
of autism, but that an additional trigger is essential to inducing
the actual expression of autism. Thus children that did not undergo
the brain growth spurt would not be vulnerable to exposure to the
trigger, whereas those that had would develop autism, once exposed
to the trigger. Hence a possible role for exposures during childhood
cannot be ruled out on the basis of these observations.
if these observations do not rule out contributions during childhood,
they clearly emphasize the need to understand what factors may be
causing autistic children to have smaller head circumference at
birth and then undergo rapid increases in brain size over the first
2 years of life.
contaminants that affect the pace and pattern of brain development
in animals, or interfere with mechanisms controlling brain development,
have become increasingly widespread in humans over the past two
decades, over the same period that autism has become more common:
disrupts the action of thyroid in directing brain development.
This contaminant is now in the drinking water of over 20 million
people in the US.
flame retardants have been found to alter the brain growth spurt
in mice; PBDE levels have increased exponential in Americans over
the past 20 years.
A activates genes involved in regulating brain growth. Exposure
to bisphenol A has become ubiquitous as a result of its use to
make polycarbonate plastic.
these clear results from Courchesne et al. showing that
brain growth patterns in the womb and postnatally differ in autistic
children, work on possible contributions by contaminants interfering
with brain development is now warranted.