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For the past 15 years, Debra Mills has been investigating a mysterious
genetic disorder called Williams syndrome. This syndrome is puzzling to
scientists because, although individuals with Williams have cognitive
deficits, they also retain some normal cognitive functioning, specifically
in the areas of language and face recognition.
The similarities among individuals who have Williams syndrome are also
remarkable. In addition to the similar cognitive abilities, they also
share similar facial features, such as a turned-up nose that gives them
an elfin-like appearance. They are also characterized as being very social:
warm, friendly and making a lot of eye contact.
The disorder is caused by a microdeletion on chromosome 7 and is associated
with abnormalities in the posterior regions of the brain, especially the
smaller parietal lobes. The accompanying cognitive deficits are related
to spatial abilities, such as difficulty drawing and getting around town.
Individuals with Williams syndrome also have general mental retardation
and usually are unable to live on their own or go through regular schooling.
Although much can be learned from the deficits caused by this syndrome,
Mills, associate professor of psychology, is particularly interested in
the brain systems that mediate the preserved cognitive functions of these
individuals.
“Are these relatively spared cognitive functions normally organized
in the brain?” Mills asked. “Or do they show abnormal organization
because of, or perhaps as a consequence of, the other abnormal brain structures.
Are those also abnormally organized? To what extent is there plasticity
for these functions?”
Mills’ research, done in collaboration with colleagues such as the
Salk Institute’s Ursula Bellugi, has used the Event Related Potential
(ERP) technique to record the electrical activity of the brain. This technique
is useful in detecting activity in response to a particular stimulus because
it is time-locked to specific events and averaged across many trials.
That means extraneous brain activity is averaged out, leaving only the
activity for the particular stimulus under examination, such as an image
of a face or a word in a sentence.
Mills has found that in individuals with the disorder, the early part
of the ERP wave form (first 200 milliseconds after stimulus) has a characteristic
signature for both faces and language. “It’s almost like a marker
for abnormal brain function,” she said.
The abnormal ERP is intriguing because it also is present in the spared
processes; the signature ERP has been found in every subject with Williams
syndrome tested in the study, which includes 60 adults and 20 children,
and not in any other population that has been tested (normal adults, patients
with brain lesions, individuals with Down syndrome, and both language-impaired
and normally functioning children).
Working with Julie Korenberg, a geneticist at UCLA, Mills is using specific
cases to form a picture of Williams syndrome. “One way we are trying
figure out this puzzle is by looking at individuals that have a partial
deletion of the area on chromosome 7 associated with Williams and then
look at their cognitive profiles and the brain structures,” Mills
said.
They have studied one person who has only part of the deletion typical
of Williams Syndrome. This man is interesting because, although he has
several features in common with other people with Williams (facial features,
increased sociability), he has preserved spatial abilities.
Using magnetic-resonance imaging to monitor this man’s brain, another
of Mills’ collaborators, Allan Reiss at Stanford University, found
that the posterior regions of his brain—those associated with spatial
abilities—are relatively normal, but areas associated with auditory-language
processing are abnormally large, just like those in other individuals
with Williams. Interestingly, they showed the ERP pattern characteristic
of Williams syndrome for language, but the ERP pattern he displayed for
face processing was normal.
Mills explained: “So all that information hangs together to say that
this area of the gene [that he retains] is probably responsible for the
abnormal spatial abilities in Williams.”
Mills, who arrived on campus this fall, and her colleagues are funded
by a grant from the National Institutes of Health. Most of the testing
has been and will be performed at the University of California-San Diego.
However, Mills also will test subjects in her newly outfitted lab at Emory,
as well as analyze data and write up results. This work will be highlighted
in the PBS show “Scientific American Frontiers,” hosted by Alan
Alda, on Nov. 13.
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