Nine new genes on the X chromosome linked to learning impairment have been unearthed by an international team of 70 researchers.
Learning disability is significantly more common in males than in females and genetic causes have long been sought on the X chromosome because males have only one X chromosome and so a gene mutation on the X is more likely to have an effect in males than in females.
"We sequenced 720 out of the approximately 800 known genes on the X chromosome in more than 200 families affected by X-linked learning disabilities," Nature Genetics quoted Professor Mike Stratton, from the Wellcome Trust Sanger Institute as saying.
"This is the largest sequencing study of complex disease ever reported," he added.
The new genes play roles in a wide range of biological processes suggesting that disruption to many cellular machines can damage the nervous system.
"As well as these important new gene discoveries relating to learning disability, we have also uncovered a small proportion - 1% or more - of X chromosome protein-coding genes that, when knocked out, appear to have no effect on the characteristics of the individual," said Stratton.
"It is remarkable that so many protein-coding genes can be lost without any apparent effect on an individual's normal existence - this is a surprising result and further research will be necessary in this area."
Same genetic variants have been linked to some characteristics in common cold.
Researchers suggest that a similar strategy can be used to find disease causing sequence variants implicated in other complex genetic diseases.
"This new research uncovers yet more genes that can be incorporated to improve the provision of diagnostics to families with learning disabilities and allow us to develop more omprehensive genetic counselling in the future, allowing parents and the extended family to make the most informed family planning decisions," said Dr Lucy Raymond, Reader in Neurogenetics, Cambridge Institute for Medical Research at the University of Cambridge.