Biology 202
2003 First Web Paper
On Serendip

To understand the human brain, looking at behavior as an indicator of brain function has led researchers to focus on individuals with Williams syndrome (1). The limitations as well as highly developed features in behavior found in people with this syndrome have attracted investigators. The unique behavior displayed has led many to believe that it may be possible to unravel brain organization by locating the damaged areas in individuals with Williams syndrome and connect them to the behavior observed in these individuals (1).

Individuals with Williams syndrome are all unique in their behavior, but most share common features. When given IQ tests they tend to receive scores that are below the average (1). The most common feature in is mental retardation, with about 95% with IQs in the mild to moderate range of retardation (3). Along with low IQ scores, these individuals tend to have limited writing and arithmetic skills. Some individuals display developed abilities to compose stories. They seem to be comfortable narrating and manipulating their voice to express their story (3). They are known for their musical talents and spoken language abilities as well as their sociable tendencies (1).

Research on individuals with Williams syndrome has led to many discoveries. One of the biggest puzzle pieces uncovered is the genetic cause of the disorder (4). A small piece missing in one of the chromosome 7 copies was found to be the cause of Williams syndrome (4). Individuals lose about 15 to more genes contained in this missing piece. About 95% of the individuals with Williams syndrome display this deletion (1). Some features of the disorder include problems with the heart, blood vessels, kidney, as well as dental problems (4). Connecting genes to physical brain abnormalities and ultimately to the observed behavior could produce an explanation as to how the developing brain is organized.

When comparing "normal" children with children with Williams syndrome behavioral differences can be observed (2). Along with the behavioral differences, brain structure differences have also been observed (2). Physically, the brain of an individual with the syndrome is discovered to be about 80% of the volume of the "normal" brain (2). The Williams syndrome brain is also characterized by a reduction of cerebral gray matter and lower cell density (2).

Knowing that there are physical differences in brain structure developments, how can we assume that the brain of a child with the disorder is simply a damaged version of the normal child with the normal brain if their genetic information is different (2) ?

The difference in genetic information leads to different a development (2). There must be a difference in the growth of the brain in the womb as well in childhood. With a set of different instructions for development in an individual with Williams syndrome, is it really surprising that their brains are different?

Williams syndrome is a disease marked by the deletion of a section of chromosome 7 that may involve several more genes (4). Individual genes don't explain the whole story leading to behavioral differences. Genes code for proteins, but not necessarily for the behavior displayed in a person (2). Recognizing that there are multiple genes involved in one function as well as the observation that one gene may also be part of many functions makes it harder to explain that the symptoms due to the deletion of a small piece of chromosome are to be entirely blamed for the condition (2). Keeping in mind the contribution of the genetic information, a person with Williams syndrome has a different developmental path than that of a person with the normal brain.

When comparing the brain of adults with Williams syndrome and that of "normal" adults, there is an assumption that the relationship between behavior and brain structure can be compared between the two. If we were to suppose that behavior is a product of the brain, but not of single divisions of the brain, then it could be that the brain of a person with Williams syndrome is producing similar behaviors as the normal brain. The behavior may not be the product of the same regions in a normal brain because we have observed that their brain is different (2).

"In other words, researchers cannot use the end state of development to make claims about the start state (5)."

This might mean that we are dealing with a brain that is not necessarily damaged, but has simply physically developed differently. We cannot simply compare a "normal" brain with an abnormal brain when they are defined by different genetic information. The brain is much more complex. The same behavior can be produced without having the same brain.

References

1) Lenhoff, Howard M. Wang, Paul P., Frank Greenberg and Ursula Bellugi. (1997, December). Williams Syndrome and the Brain. Scientific American. 68-73. from http://www.sciamarchive.org

2)Institute of Child Health, Crucial Differences Between Developmental Cognitive Neuroscience and Adult Neuropsychology, by Annette Karmiloff-Smith.

3)Center for Research in Language, Williams Syndrome: An Unusual Neuropsychological Profile by Ursula Bellugi, Paul P. Wang, and Terry L. Jernigan.

4)National Center for Biotechnology Information, Genes and Disease information

5)Guardian Unlimited newspaper, Summary of lecture by Annette Karmiloff-Smith.


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