Missing genetic information key to severe learning disorders

13 August 2006

Scientists have discovered a genetic anomaly responsible for severe learning difficulties. Using a new technique for detailed examination of human chromosomes, researchers at the Wellcome Trust Sanger Institute in Cambridge have identified a missing piece of genetic information, which they believe may be a common cause of learning difficulties. The results are published online today in 'Nature Genetics'.

"It seems that people with some forms of severe learning difficulties have a small but important section of chromosome 17 missing, which appears to have been deleted during meiosis, the process by which the egg and sperm are produced," explains Dr Charles Shaw-Smith, a University of Cambridge researcher based at the Institute. "The deletion occurs in a region of the genome known for its complexity of organisation, and also for its association with neurodegenerative disorders, including rare heritable forms of dementia. However, this is the first time that the region has been associated with learning difficulties in children."

During meiosis, chromosomes are copied before lining up to exchange material. However, if the copying mechanism goes wrong, the chromosomes line up out of synch and the genetic material gets mispaired. Dr Shaw-Smith likens this to lining up the buttons and holes wrongly on a shirt so that they don't pair up properly. It is during this process that genetic material can get deleted.

Dr Shaw-Smith's team, led by Dr Nigel Carter at the Wellcome Trust Sanger Institute, used a technique known as 'array-based comparative genomic hybridisation' to identify the missing piece of genetic information. This technique allows human chromosomes to be studied at much higher resolution than was previously possible. Identification of patients with this condition was greatly helped by the DECIPHER online database, developed through a second Cambridge University/Sanger Institute collaboration, whereby information about patients with rare chromosome disorders is logged and made available to the international clinical genetics community. This led to the identification of the deletion of part of chromosome 17, also identified by groups in the USA and the Netherlands.

"We believe that the loss of genetic material on chromosome 17 may prove to be a relatively common cause of learning difficulties," says Dr Shaw-Smith.

Scientists have previously managed to decode the human genome, often referred to as 'the book of life'. Since completion of the Human Genome Project, which enabled this decoding and was part-funded by the Wellcome Trust, researchers at the Sanger Institute have been exploiting the new knowledge and applying new techniques to better understand the complexities of the human genome and how variations can lead to diseases and disorders.

Contact

Mike Findlay
Media Officer
Wellcome Trust
T 020 7611 8612

M 07973 481485
E c.brierley@wellcome.ac.uk

Notes for editors

1. The Wellcome Trust is the most diverse biomedical research charity in the world, spending about £450 million every year both in the UK and internationally to support and promote research that will improve the health of humans and animals. The Trust was established under the will of Sir Henry Wellcome, and is funded from a private endowment, which is managed with long-term stability and growth in mind.

2. The Wellcome Trust Sanger Institute, which receives the majority of its funding from the Wellcome Trust, was founded in 1992 as the focus for UK sequencing efforts. The Sanger Institute is responsible for the completion of the sequence of approximately one-third of the human genome as well as genomes of model organisms such as mouse and zebrafish, and more than 90 pathogen genomes. In October 2005, new funding was awarded by the Wellcome Trust to enable the Institute to build on its world-class scientific achievements and exploit the wealth of genome data now available to answer important questions about health and disease. These programmes are built around a faculty of more than 30 senior researchers. The Wellcome Trust Sanger Institute is based in Hinxton, Cambridge, UK.

3. 'Microdeletion encompassing MAPT at chromosome 17q21.3 is associated with developmental delay and learning disability' is scheduled for advance online publication (AOP) on the 'Nature Genetics' website on 13 August at 18.00 London time/13.00 US Eastern time. (Please note that this link will not work until the paper is published.)