INTRODUCTION

Learning disability: anintroductionGregory O’Brien

Angela Hassiotis

Abstract‘Learning disability’ is a term used in the UK that corresponds to the inter-

nationally used ‘mental retardation’. It is determined by low IQ, impaired

social adaptation and onset within the developmental period; classifica-

tion is primarily by IQ. The prevalence of learning disability is rising,

mainly due to improved longevity. Several psychiatric disorders are very

common among people with learning disability. Promoting the social

inclusion of this vulnerable group is one of the greatest challenges to

any developed society.

Keywords learning disability; mental retardation; psychiatric disorder;

social inclusion

Terminology

‘Learning disability’ is a uniquely British term that corresponds

to the condition ‘mental retardation’, as defined and described in

the two standard, internationally used classification systems, the

DSM-IV and ICD-10.1,2 The term previously used in the UK was

‘mental handicap’. In recent years, the terms ‘developmental

disability’ and ‘intellectual disability’ are also used internation-

ally. People affected by learning disability have low intelligence,

limited capacity for independence and a range of additional

physical disabilities; the latter two features being more

pronounced among individuals with more severe intellectual

disability (i.e. lower IQ).

Definition

There are three elements to the definition of learning disability:

� Intelligence level at least two standard deviations below the

population mean (intelligence quotient (IQ) <70).

� Onset of this condition ‘within the developmental period’ e

this is not further defined in ICD, but is described in DSM by

onset up to the age of 18 years.

Gregory O’Brien MA FRCPsych FRCPCH MD is Professor of Developmental

Psychiatry at the University of Northumbria and Northgate Hospital,

Morpeth, UK. His research interests include outcome studies in learning

disability and the biological basis of behaviour disorder in develop-

mental disability. Conflicts of interest: none declared.

Angela Hassiotis MA FRCPsych PhD is a Senior Lecturer in the Psychiatry of

Learning Disabilities at University College London and Honorary

Consultant Psychiatrist in the Camden Learning Disabilities Service. Her

research interests include health service research, epidemiology and

psychological interventions for mental disorders and problem behav-

iours in this population. Conflicts of interest: none declared.

PSYCHIATRY 8:10 37

� Significant associated impairment of social functioning or

capacity for independence.

Intelligence quotient (IQ) and intelligence testing

Identification of low IQ (<70) is one of the crucial elements in the

detection and assessment of learning disability. IQ is defined by

the following formula:

IQ ¼ mental age/chronological age � 100

Intelligence testing is a controversial and complex matter: low

scores can have far-reaching consequences and can be the result

of influences other than low intelligence. Variables that can affect

test performance include the following.

Cultural differences: many of the most commonly used IQ tests

are designed for use in western society, and many of the items

are culturally specific. This highlights the difficulty in testing

ethnic-minority population groups.

Language: IQ tests are written in English, and difficulties can

arise when IQ tests are administered to individuals who do not

have English as their first language. Poor test scores could be

a reflection of language difficulties rather than IQ itself.

Performance: how the individual performs on the day of the test

can influence the result (e.g. tiredness and poor concentration

can affect performance). Examiners control for such factors by

conducting the tests in a quiet location and providing rest

opportunities to avoid fatigue.

Classification

Learning disability is classified according to the severity of

intellectual disability (see Table 1). The concept of profound

learning disability is seldom used in clinical practice e such low

IQ scores have little utility because psychologists find that IQ

tests are unreliable at this level of functioning. Other approaches

have therefore employed assessments of everyday living skills to

describe the more severe degrees of learning disability. One

approach proposed by the American Psychological Association

(www.apa.org) takes this further by classifying according to the

intensity of personal support the individual requires to attain

quality of life. However, even this system relies on IQ <70 as

a base entry criterion into the overall group or condition of

learning disability e for now, it looks as though intelligence

testing is here to stay.

Classification of learning disability

Severity IQ

Mild 50e69

Moderate 35e49

Severe 20e34

Profound <20

Table 1

3 � 2009 Elsevier Ltd. All rights reserved.

INTRODUCTION

Incidence and prevalence

The incidence of learning disability in a population is primarily

a product of:

� natural variation of intelligence/IQ in the population, which

tells us that at least 2.5% of a population have an IQ <70,

based on normal distribution.

� rates of genetic and acquired causes of brain maldevelopment

and damage, which add additional cases above and beyond those

derived from the normal distribution of IQ in the population.

The prevalence of learning disability depends on the inci-

dence, and on factors such as migration and especially longevity.

The most recent estimates of prevalence according to level of

disability are:

� mild learning disability (IQ 50e69): 2.5% of population. In

England: 2.5%�48 million ¼ 1.2 million

� moderate, severe and profound learning disability in England:

>0.4%�48 million ¼ 210,000.

Overall, the UK Government estimate is that the prevalence of

learning disability is currently increasing by a factor of 1% each

year, and will do so at least until 2010 (see Table 2).

Learning disability and social inclusion

The definition of learning disability is, in a sense, a social

construct. Given that the definition includes an element of

impaired social functioning, it follows that the extent to which

society attempts to adapt or include the individual is crucial to

whether that individual falls into the definition: in essence,

whether he or she is handicapped by having a low IQ. Following

this line of thinking to its logical conclusion might lead one to

think that learning disability is entirely a social construct. But,

when one considers the situation of individuals with very severe

intellectual disability, it is clear that the two (intellectual

disability and social inclusion) interact. There have been major

advances recently in social inclusion for people with intellectual

disability, and it is now accepted that many individuals who

were previously regarded as requiring custodial care, can e with

support and help e attain more fulfilling lives. One of the most

socially excluding factors can be a person’s behaviour, whether

due to mental illness or some other cause.

Developments affecting the incidence and prevalenceof learning disability in the UK

Development Incidence Prevalence

Genetic screening Y Y

Current UK migration patterns [ [

Developments in education e Y

Improved survival

of brain-damaged children

[ [[

Improved healthcare

for adults with disabilities

e [[

Increased longevity in older

people with learning disability

e [[

Table 2

PSYCHIATRY 8:10 37

Psychiatric disorder in learning disability: introductory comments

Psychiatric problems that are more common in learning disability

include:

Attention Deficit Hyperactivity Disorder (ADHD) e this

disorder is much more common among learning-disabled adults

than in the normal population, where it is mainly a disorder of

childhood.

Autism e by far the most common psychiatric disorder

among people with learning disability, affecting 10% overall and

30% of those in the moderate-to-severe (IQ < 50) group.

Depression and bipolar disorder e these affect people with

learning disability at a rate of at least twice that of the general

population and are difficult to diagnose among severely learning-

disabled subjects.

Schizophrenia eaffects people with learning disability at a rate

of at least twice that of the general population, where it is also

difficult to diagnose among severely learning-disabled subjects.

Self injury e a common problem among severely learning-

disabled people, where it often takes the form of biting, scratching

or head-banging. It may be best understood as a self-stimulatory

behaviour, but, where these problems occur in subjects who have

no previous history, it is important to first consider and assess

a local physical health problem, and also depression.

Recent changes in policy

The UK Government published the White Paper for services and

rights of people with learning disability in England, entitled

Valuing people.3 This document aimed to achieve real change in

the lives of people with learning disabilities, increasing their

participation in the community, recognizing their equal status as

citizens, and increasing choice and opportunities. In January

2009, a revised document (Valuing people now)4 took stock of

what had occurred since the publication of Valuing People and

set out the targets for the next three years. These include:

personalization, what people do during the day, better health,

access to housing, and making sure that change happens. A

REFERENCES

1 American Psychiatric Association. Diagnostic and statistical manual of

mental disorders (DSMeIV). 4th edn. Washington, DC: American

Psychiatric Association; 1994.

2 World Health Organization. The ICD-10 classification of mental and

behavioural disorders: clinical descriptions and diagnostic guidelines.

Geneva: WHO; 1992.

3 Department of Health. Valuing people: a new strategy for learning

disability for the 21st century. London: HMSO. Also available at: http://

www.archive.official-documents.co.uk/document/; 2001.

4 Department of Health. Valuing people now: from progress to trans-

formation e a consultation on the next three years of learning

disability policy. Also available at: http://www.dh.gov.uk/en/

Consultations/Closedconsultations/DH_081014 (accessed May 2009).

4 � 2009 Elsevier Ltd. All rights reserved.

INTRODUCTION

Further reading for Learning Disability

It is, of course, impossible to cover the whole spectrum of what is an active field both in terms of research and innovative clinical practice aided by

ground-breaking government policies. This new edition of Psychiatry’s Learning Disability chapter builds on the previous edition by including

a more specific focus on mental health, including updates on psychopathology and current treatment options.

As the previous and present Chapter Editors, we recommend that you look at the articles in the previous 2006 edition of the chapter. Many of

the previously published articles provide useful background detail on aetiology of learning disability and policy context, and others complement

or offer more detailed expositions of the topics in the present edition. The previous articles on assessment and classification, and functional

analysis of behaviours, are particularly useful for trainees and medical undergraduates.

Assessment

C Assessment and classification of psychiatric disorders in adults with learning disabilities

Sally-Ann Cooper, Neill Simpson. Psychiatry 2006; 5: 306e11

C Functional analysis and challenging behaviour

Theresa Joyce. Psychiatry 2006; 5: 312e15

Presentation and comorbidityC Psychiatric morbidity in adults with Down syndrome

Vee P. Prasher, Dale Lawrence. Psychiatry 2006; 5: 316e9

C Autism spectrum disorders

Patricia Howlin. Psychiatry 2006; 5: 320e4

C Fragile-X syndrome

Manga Sabaratnam. Psychiatry 2006; 5: 325e30

C Behavioural phenotypes in adulthood

Gregory O’Brien. Psychiatry 2006; 5: 331e6

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