In a study published in the February 2003 issue of Nature Medicine, a group of collaborators from across the globe reports that abnormalities in vascular endothelial growth factor, or VEGF, is a cause of DiGeorge syndrome. The syndrome can cause a wide range of heart defects, many of which are vascular in nature, as well as problems with the thymus and parathyroid gland, craniofacial abnormalities and mental retardation.
"We have found one of the downstream target genes," said Dr. Simon J. Conway, developmental biologist at the Medical College of Georgia and a senior author on the Nature Medicine paper along with Dr. Peter Carmeliet, director of The Center for Transgenic Technology at Katholieke Universiteit Leuven in Belgium. One next step would be to find why these VEGF defects occur with an ultimate goal of trying to prevent them, Dr. Conway said.
Researchers found this target "downstream" of human chromosome 22, which is known to be deleted in 60 to 70 percent of people with DiGeorge syndrome. Deletion of chromosome 22 removes a group of 24 genes as well, many of which are transcription genes known to control many downstream targets. Although the targets remain largely unknown, it's believed that these 24 genes control hundreds, maybe thousands, of downstream genes, which helps explain the complexity of the syndrome that can result when the chromosome is deleted, Dr. Conway said.
One of those 24 genes is Tbx1, which is widely considered the primary gene involved in DiGeorge syndrome, he said. In 2001, several research groups published their findings on mice models lacking Tbx1; those mice had some, but not all, the defects found in humans. In fact, although Tbx1 seems to have a role in DiGeorge and it may be
Contact: Toni Baker
Medical College of Georgia