What causes learning disabilities?

Up to 1 in 50 children have learning disabilities.^1,2 The reasons for their problems are often unknown. Researchers are hunting down the genetic causes of learning disabilities. They hope to give more people a clear diagnosis. This would help people access appropriate support and provide information for the entire family on how the condition is inherited.

Contents

• What's the problem and who does it affect?
• What is the project trying to achieve?
• What are the researchers' credentials?
• Who stands to benefit from this research and how?
• References

What's the problem and who does it affect?

Many people with learning disabilities lack a clear diagnosis

Up to two percent of children have learning disabilities.^1,2 The condition often runs in families, but only half of those affected have a clear diagnosis.³

Without a proper diagnosis, it can be difficult for parents, teachers and healthcare professionals to anticipate what kind of help and support a child will need as he, or she, grows up. People with severe learning difficulties can need help with all sorts of basic everyday things, such as getting dressed, washing and eating. Many suffer from other conditions as well, including cerebral palsy, epilepsy and autism. Some need round-the clock care for their entire lives. In contrast, people with mild disabilities may only need additional help at school.

Without a diagnosis, people in families affected by learning disabilities tend to worry about whether or not they will pass the condition on to any children they might have in the future. Assessing this risk can be very difficult, making pregnancy an extremely anxious time.

What is the project trying to achieve?

Hunting for genes for learning disabilities

Around 30% more boys than girls have learning disabilities.^1,3,4,5,6,7. Researchers working on this project are therefore looking for mutations in genes on the X chromosome, as it is this chromosome that differs between the sexes.

Previous studies have already identified mutations that cause learning disabilities in more than 20 different genes on the X chromosome. They involve very small changes in the coding sequences in the genes. But many people with X-linked learning disabilities do not carry these mutations, and the genetic cause of their condition remains unknown.

This project will identify whether much bigger changes in the coding sequence, known as ‘copy number’ changes, can also cause learning disabilities. Researchers suspect that these bigger changes, which involve the loss or gain of an entire copy of a gene, might be a common cause of learning disabilities. Studies of these bigger changes have only just become possible thanks to newly developed techniques.

What are the researchers' credentials?

We do not provide medical advice. If you would like more information about a condition or would like to talk to someone about your health, contact NHS Choices or speak to your GP.

The project team, based in Cambridge, has studied the genetic causes of learning disability for a number of years. They are leaders in the field, both within the UK and internationally, and have published extensively.

Dr Lucy Raymond has established a large international study, called the GOLD (Genetics of Learning Disability) study, to identify novel genes and causes of X-linked learning disability. The team’s earlier work on GOLD means they are extremely well equipped to carry out this project, as they have already collected genetic material from 600 families who all have at least two male individuals with learning disabilities. This collection is one of the two largest in the world and participating families are keen that this work should continue.

Who stands to benefit from this research and how?

A clear diagnosis for more people

The ultimate goal of this project is to ensure more people with learning disabilities get a clear diagnosis, with a full explanation as to the genetic causes of their condition.

The first people to benefit are likely to be the families who are taking part in the project. Researchers hope to reveal previously unknown mutations that cause the learning disabilities in these families.

Many more families may benefit in the future. The project team hopes to provide information needed to develop new diagnostic tests for use within the NHS.

Helping children fulfil their potential

A proper diagnosis is invaluable to families affected by learning disabilities. It explains the cause of the disabilities and helps parents of disabled children to find the best type of individualised care for their child – the right healthcare, support from social services, schooling and so on. Tailoring this support helps ensure children achieve their full potential. A clear diagnosis also means everyone in the family has the information they need to assess whether they are at risk of having a child with learning disabilities.

References

1. McLaren J, Bryson SE. Review of recent epidemiological studies of mental retardation: prevalence, associated disorders, and etiology. Am J Ment Retard 1987;92(3):243-54.
2. Boyle CA Yeargin-Alsopp M, Doernberg NS, Holmgreen P, Murphy CC, Schendel D. Prevalence of selected developmental disabilities in children 3-10 years of age: the Metropolitan Atlanta Developmental Disabilities Surveillance Program. Morbidity and Mortality Weekly Report 1991;45:1-14
3. Stevenson RE, Schwartz CE, Schroer RJ. Mental retardation in South Carolina. I Characteristics of the study population. Proc Greenwood Genet Center 1996;15:26.
4. Penrose L (1938) A clinical and genetic study of 1280 cases of mental defect. Vol 229. HMSO
5. Drillien CM. The incidence of mental and physical handicaps in school age children of very low birth weight. II. Pediatrics 1967;39(2):238-47.
6. Baird PA, Sadovnick AD. Mental retardation in over half-a-million consecutive livebirths: an epidemiological study. Am J Ment Defic 1985;89(4):323-30.
7. Stoller A. Epidemiology of mental deficiency in Victoria. Proceedings of the Fourth Interstate Conference on Mental Deficiency 1965:18-28.