Men-tal research

Sita Dinanauth - Science Editor 8 June 2009

Collaborative research involving 70 researchers worldwide, including geneticists from Cambridge University, have found nine brand new genes on the X chromosome which are inextricably linked to learning disabilities.

The findings, published by the science journal Nature Genetics, define mental retardation as a disability characterized by ‘‘significant limitations both in intellectual functioning and in adaptive behaviour as expressed in conceptual, social and practical adaptive skills” with onset before the age of 18 years.
The study used DNA sequencing technology to detect as many new ‘abnormal’ genes as possible.

Professor Mike Stratton from the Wellcome Trust Sanger Institute said,”this is the largest sequencing study of complex disease ever reported.”
He then explained, “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.”

In the future similar strategy will be used to find disease causing sequence variants implicated in other complex genetic diseases.

Mental retardation is more common in males than females as males have only one X chromosome and a gene mutation on the X chromosome is more likely to be compensated for by another X Chromosome present in females. X linked disorders have been well studied by geneticists over the past decade.

The study also produced other interesting findings: “As well as these important new gene discoveries relating to mental retardation, 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. It is remarkable that so many protein-coding genes can be lost without any apparent effect on an individual’s normal existence.”

Dr Lucy Raymond, Reader in Neurogenetics at the University of Cambridge Institute for Medical Research, who was also an author of the paper said, “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 comprehensive genetic counselling in the future, allowing parents and the extended family to make the most informed family planning decisions.”

Sita Dinanauth – Science Editor