October 29, 2001
Scientists identify new genetic mechanism for disease
Scientists at The Hospital for Sick Children (SickKids) and the University of Toronto (U of T) have identified a previously unknown genetic basis for Williams syndrome. This finding also points to a new genetic mechanism for disease. This research is published in the cover article of the November issue of the scientific journal Nature Genetics.
"We found children who manifested the characteristics of Williams syndrome, but who did not have the classic deletion on chromosome 7. Instead, they had the same segment of chromosome 7 inverted, or flipped. We also found that many of the parents of children with Williams syndrome apparently had the same inverted segment of DNA of chromosome 7. Our findings have large implications for the diagnosis of this disorder and corresponding genetic counseling," said Dr. Lucy Osborne, the study's lead author and an assistant professor in the Departments of Medicine and Molecular and Medical Genetics at the University of Toronto.
Williams syndrome is a genetic condition (estimated to occur in one in 20,000 people worldwide) which causes medical and developmental problems. Children with Williams syndrome have a developmental delay and learning disabilities, and medical problems including heart or blood vessel problems, and kidney abnormalities. Children with Williams syndrome are known for often having musical interest as well as a being extremely friendly and loving, but also demonstrating anxiety. Seventy per cent of these children also have attention deficit hyperactivity disorder. The majority of children with Williams syndrome have a deletion of about 20 genes on a segment on one chromosome 7.
"In Williams syndrome, the inversion appears to sometimes lead to symptoms of the disorder or a predisposition of the chromosome to deletion in the next generation," said Dr. Stephen Scherer, the study's senior author, a senior scientist at The Hospital for Sick Children and an associate professor in the Department of Molecular and Medical Genetics at U of T. "This research points to another genetic mechanism for disease - DNA inversion."
It seems to be holding true that the DNA in the genome of any two individuals is 99.9 per cent identical in content. However, this new discovery suggests that in some cases, the flipping of words or sentences within each individual's genetic dictionary (or genome) can contribute to their unique characteristics, and also influence their offspring. In this case, an inversion on chromosome 7 is involved in Williams syndrome. In another recent study, chromosome 15 anomalies were observed in individuals with panic and anxiety disorder.
"It is possible that the phenomena of chromosome imbalances may also be found in other neuropsychiatric conditions such as autism and schizophrenia, or perhaps even in some behavioral traits all of us have," Dr. Scherer added.
Dr. Scherer and Dr. Osborne are holders of New Investigators Awards from the Canadian Institutes of Health Research.
This research was supported by the Canadian Institutes of Health Research, the Canadian Genetic Diseases Network, The Centre for Applied Genomics at The Hospital for Sick Children, and The Hospital for Sick Children Foundation.
The Hospital for Sick Children is a health care, teaching and research centre dedicated exclusively to children; affiliated with the University of Toronto. Its mission is to provide the best in family-centred, compassionate care, to lead in scientific and clinical advancement, and to prepare the next generation of leaders in child health. For more information, please visit www,sickkids.ca.
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