INTRODUCTION

Learning disability: an introductionGregory O’Brien

AbstractLearning disability is a UK term corresponding to ‘mental retardation’ in

international usage. Definition depends on low IQ, impaired social adapta-

tion and onset within the developmental period; classification is primarily

by IQ. The prevalence of learning disability is rising, mainly due to improved

longevity. A number of psychiatric disorders are very common among peo-

ple with learning disability. Promoting the social inclusion of this vulnerable

group is one the greatest challenges to any developed society.

Keywords learning disability; mental retardation; psychiatric disorder;

social inclusion

Terminology

‘Learning disability’ is a uniquely British term, which 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 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 intellec-tual disability (i.e. lower IQ). The term for learning disability used previously in the UK was ‘mental handicap’.

Definition

There are three elements of the definition of learning disability/mental retardation. • Intelligence level at least two standard deviations below the population mean (intelligence quotient (IQ)  <  70). • Onset of this condition ‘within the developmental period’ – this is not further defined in ICD, but is described in DSM by onset up to the age of 18 years. • Significant associated impairment of social functioning or capacity for independence.

Intelligence quotient (IQ) and intelligence testingIdentification of low IQ (<70) is one of the crucial elements in the detection and assessment of learning disability. IQ is defined using the following formula:

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

developmental disability.

PSYCHIATRY 5:9 29

IQmental 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 oppor-tunities to avoid fatigue.

Classification

Learning disability is classified according to the severity of intel-lectual disability (see Table 1). The concept of profound learn-ing disability is seldom used in clinical practice – such low IQ scores have little utility because psychologists find that IQ tests are unreliable at this level of functioning. Other approaches have there-fore employed assessments of everyday living skills to describe the more severe degrees of learning disability. One new approach proposed by the American Psychological Association takes this further, by classifying according to the intensity of personal sup-port the individual requires to attain quality of life. However, even this system relies on IQ under 70 as a base entry criterion into the overall group or condition of mental retardation – for now, it looks as though intelligence testing is here to stay.

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.

Classification of learning disability

Severity IQ

Mild 50–69

Moderate 35–49

Severe 20–34

Profound < 20

Table 1

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INTRODUCTION

• 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 incidence, and on factors such as migration and especially longevity (see below).

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 func-tioning, 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 con-clusion 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 (intel-lectual disability and social inclusion) interact. There have been major advances recently in social inclusion for people with intel-lectual disability, and it is now accepted that many individuals who were previously regarded as requiring custodial care, can – with support and help – 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. These issues are introduced in the following section and dis-cussed at greater length on pages 331–336.

Psychiatric disorder in learning disability: introductory comments

Psychiatric problems that are more common in learning disabil-ity include:

Attention Deficit Hyperactivity Disorder (ADHD) – this disor-der is much more common among learning disabled adults than in the normal population, where it is mainly a disorder of childhood.

Autism – 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.

Conduct disorder – disruptive, noisy, disorganized and gen-erally overactive behaviour is very common, especially in the severely learning disabled group, where it is often referred to as ‘challenging behaviour’.

Depression and bipolar disorder – 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.

Pica – the consumption of either non-food materials or of inappropriate foods (e.g. dry coffee powder; uncooked meats) is a common problem among severely learning disabled indi-viduals, where it often has a compulsive quality.

Schizophrenia also affects 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 – a common problem among severely learning dis-abled 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

PSYCHIATRY 5:9 294

no previous history, it is important to first consider and assess a local physical health problem, and also depression.

Sleep disorders – unstable sleep rhythm is a common fea-ture of people with learning disability, particularly among certain aetiologies of learning disability, notably tuberous sclerosis.

Valuing People and learning disability

The UK Government has recently produced a White Paper for services and rights of people with learning disability in England, entitled Valuing People.3 This document reviews the changing epidemiology of learning disability, highlighting recent and cur-rent changes (parallel documents for Scotland and Wales are Same as You and Meeting the Challenges, respectively).

The most recent estimates of prevalence are: • mild learning disability (IQ 50–69): 2.5% of population. In

England: 2.5%  ×  48 million  =  1.2 million • moderate, severe and profound learning disability in England:

>0.4%  ×  48 million  =  210,000. Significant changes are occurring concerning the incidence and prevalence of learning disability (see Table 2 and also pages 302–305). 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. ◆

RefeRenCeS

1 American Psychiatric Association. Diagnostic and statistical manual

of mental disorders (DSM–IV). 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, 2001. Available

at: http://www.archive.official-documents.co.uk/document/

cm50/5086/5086.htm

Developments affecting the incidence and prevalence of learning disability in the UK

Development Incidence Prevalence

Genetic screening ↓ ↓Current UK migration patterns ↑ ↑Developments in education – ↓Improved survival of

brain-damaged children

↑ ↑↑

Improved healthcare for adults

with disabilities

– ↑↑

Increased longevity in older

people with learning disability

– ↑↑

Table 2

© 2006 Elsevier Ltd. All rights reserved.