New learning disability genes identified
24 April 2009
An international team of researchers, including scientists from the Wellcome Trust Sanger Institute, showed that damage or disruption to the genes - all located on the X chromosome - was the likely cause of mental retardation.
Learning disabilities are significantly more common in men than women. Since men have only one X chromosome (the other sex chromosome being Y), genetic links have long been suspected.
In the study, the researchers recruited men from 208 families with signs of X-linked mental retardation and sequenced 720 of the 800 or so genes known on the X chromosome.
The nine genes with the strongest links to the condition are involved in a wide range of biological processes suggesting that disruption to many cellular functions can cause damage to the nervous system.
"This new research uncovers yet more genes that can be used to improve diagnostics for families with learning disabilities and allow us to develop more comprehensive genetic counselling in the future," said Dr Lucy Raymond, from the Cambridge Institute for Medical Research at the University of Cambridge, one of the researchers on the study.
Along with the new genes, the study also revealed that disruption to about 1 to 2 per cent of X chromosome genes seem to have no effect on an individual.
"It is remarkable that so many protein-coding genes can be lost without any apparent effect on an individual's normal existence,” said Professor Mike Stratton from the Wellcome Trust Sanger Institute. "This is a surprising result and further research will be necessary in this area."
Image: Brothers with Fragile X syndrome, an X chromosome-linked condition with symptoms including varying degrees of mental retardation; Wellcome Library, London
References
Tarpey P S et al. A systematic, large-scale resequencing screen of X-chromosome coding exons in mental retardation. Nature Genetics 19 April 2009, published online before print.