Two genes in particular, GTF2IRD1 and GTF2I, caught Korenberg's eye. Both encode transcription factors that help regulate the activity of other genes. Although their exact function is unknown, the genes are active in many body tissues and appear to be particularly important in regulating brain and skeletal muscle genes.
In earlier studies, Korenberg and her collaborators linked both GTF2I and GTF2IRD1 to deficits in visual-spatial processing, a hallmark of Williams Syndrome. The researchers are now dissecting the genes' roles even more. "Further parsing the effects of GTF2IRD1 versus GTF2I on spatial construction and social behavior was previously hampered by the small number of cases with fewer than the usual gene deletions and limited cognitive data," explains Korenberg.
To distinguish the roles of the two genes, postdoctoral researcher and study first author Li Dai, Ph.D., combed the genomes of 17 Williams Syndrome patients to identify those who had lost only one GTF2I gene. This allowed identification of a girl who had retained GTF2I but didn't fit the classical description of the disorder. "Finding this girl was very exciting," Korenberg said. "Her case had so much power to explain the role of these genes."
When the Salk researchers tested the girl to measure her IQ and social behavior, they found her scores in vocabulary, information processing, comprehension, arithmetic, and the ability to finish partially completed drawings to be substantially closer to normal than most patients with Williams syndrome.
Her full-spectrum IQ, a measure of both functional and performance intelligence, was 78, a full 18 points higher than average for someone with the disorder. Yet in two areas, the ability to assemble objects or work through a maze, the girl scored lower than average for people with the syndrome and substantially lower than normal.
These tests also confirmed that her social behavior is different than expected. While she is charming and engaging, she does not run up to people and does not maintain as much eye contact or physical proximity to others when conversing.
"Because she has the typical facial features and severe deficits in visual spatial skills, but lacks the overly social behavior, it suggested to us that GTF2IRD1 contributes to visual-spatial performance while GTF2I plays a role in social behavior," says Korenberg.
Although this work presents a major step forward in linking GTF2I to social behavior, it does not mean they are the only genes involved, Korenberg notes. Endowed with the power to control the activity of other genes, GTF2I might regulate signal pathways determining the structure and function of the brain or the production of neurohormones such as vasopressin and oxytoxin. Oxytoxin plays a key role in the desire to seek social interactions and trusting others, which might explain why for children with Williams syndrome, the world has no strangers, only friends.
Thursday, February 12, 2009
Two Genes Influence Social Behavior, Visual-spatial Performance In People With Williams Syndrome