CHAPTER 1: WHAT
IS LEARNING DISABILITY?
David Clarke
In
early1990s the Department of Health adopted the term learning disability as the
successor to terms such as learning difficulty (which is still used with regard
to the education of children), mental handicap, mental subnormality, and mental
deficiency. The term disability is preferable to handicap, because it describes
the effect of lower than average intelligence in a manner consistent with the
World Health Organisation definitions of impairment, disability and handicap
(WHO,1980).
An
impairment is a loss or abnormality of structure or function including
psychological functioning, a disability a restriction or lack of ability to
perform an activity within the range considered normal for a human being, and
a handicap a disadvantage
resulting from an impairment or disability that limits or prevents the
fulfilment of a normal role (WHO,1981). In other words, a handicap is something
which is imposed on a disability which makes it more limiting than it must
necessarily be, just as weight or score handicap is added in horse racing or
golf. The example of Lesch- Nyhan syndrome can be used to illustrate these
concepts further. This is an X- linked genetic disorder, caused by a deficiency
of an enzyme called hypoxanthine-guanine phosphoribosyl transferase. The enzyme
deficiency (the disease) causes altered neuronal functioning (the impairment),
resulting in learning disability and neuromuscular problems such as muscular
stiffness and movement problems (the disability). The enzyme lack also results
in a very unusual and severe form of self injury in which affected men bite
their fingers and lips, causing severe self injury. They often try to prevent
such injury by self restraint. As a result, other people may avoid affected men
in social situations, and have low expectations of them (creating a handicap).
The
term Learning Disability is also preferred by some users of services. Others
dislike most or all of the terms used. Some service users and carers feel that
terms such as “learning difficulty” and “learning disability” understate
their problems, many of which have nothing to do with the ability to learn. One
of the reasons for change in terminology over the years is that in time they
acquired pejorative overtones, in a similar way to the term ‘spastic’.
In the
international scientific literature the term mental retardation is used. This
term has been defined as an intellectual impairment, arising in the early
developmental period, which may lead to disability (if it significantly affects
social functioning) or handicap (if the individual is totally dependent on
special services).
Mental
retardation is the preferred term in North American countries, and has been
adopted by the World Health Organization in the Tenth Revision of the
International Classification of Diseases (ICD-10; World Health Organization,
1992). Here it is defined as a condition of arrested or incomplete development
of the mind, which is especially characterised by impairment, during the
developmental period, of skills which contribute to the overall level of
intelligence, i.e., cognitive, language, motor and social abilities. People with
learning disability have an overall pattern of intellectual functioning
that is significantly lower than that of the general population, with
associated impairments in social functioning. The cognitive impairment must have
occurred during the period of cognitive development (in practice often taken to
mean before the age of 18). This means that, if they were assessed using a
standardised intelligence test, they would
A typical IQ
test for adults such as the Wechsler Adult Intelligence Scale - Revised (WAIS-R)
quantifies different types of mental ability and groups them as verbal and
non-verbal scales. The sub-scales allow effects related to dysfunction of
specific brain areas, educational underachievement, etc., to be assessed. The
full scale IQ score resulting from a WAIS-R test has been designed to compare
the person tested with scores obtained from testing a large population of people
of varying abilities. Intelligence is normally distributed, like other
attributes such as height and weight. This means that, in a typical population,
most people will have scores close to average, with few people achieving very
high or very low scores (Figure 1). IQ tests such as the WAIS-R are therefore
constructed and scored so that the average (mean) score is 100 and the standard
deviation is 15 points. Anyone with a score greater than 2 standard deviations
below the average (i.e. an IQ less than 70) can be said to have a statistically
significantly low IQ if the test used is appropriate to the person tested, and
properly conducted and scored. In some circumstances IQ tests do not reflect
"real" abilities. It would, for example, be inappropriate to test a
person who did not speak English with verbal IQ test items in English. Similar,
but more subtle considerations apply to other aspects of testing, such as the
influence of cultural values and expectations. In spite of these potential
difficulties, IQ tests are the most accurate method of comprehensively assessing
cognitive ability. They are widely used to decide, for example, whether people
facing criminal charges should be dealt with through the criminal justice system
or within the health service. They are not routinely used to assess cognitive
ability in nursing, psychological or psychiatric practice, because less formal
methods of assessing abilities and problems are usually more straightforward,
less time consuming and less costly, and just as effective.
The approach
adopted in ICD-10 is to describe the typical abilities of people with a
particular severity of learning disability to allow a comparison with the person
being assessed. This approach assumes uniformity in the severity of problems
(e.g. in self-care skills and language development), whereas some people with
learning disability will inevitably have some areas of relative strength, and
others of relative weakness. Table 1 summarises the clinical descriptions of
different severities of learning disability as outlined in ICD-10, and shows how
these relate to the accepted categories of mild, moderate, severe and profound
learning disability. Thus adults
with mild learning disability will have a mental age from 9 to under 12 years.
They are likely to have had learning difficulties at school. Many adults will be
able to work and maintain good social relationships and contribute to society.
Adults with moderate learning disabilities may have a mental age from 6
to under 9 years. They are likely to have had marked developmental delays in
childhood but most often can learn to develop some degree of independence in
self care and acquire adequate communication and academic skills. Adults will
need varying degrees of support to live and work in the community. Adults with
severe learning disabilities may have a mental age between about 3 and 6 years
and are likely always to need support. Those with profound learning disabilities
have a mental age below 3 years in adulthood. They have severe limitations in
self care, continence , communication and mobility (World Health Organization,
1992).
In
most post-industrial societies people with an IQ of less than 70 are placed at a
relative economic (and hence social) disadvantage, and anyone with an IQ below
50 would be most unlikely to be able to live independently or obtain employment.
For people with IQs between 50 and 70, much depends on other factors such as
their personality, coping abilities and strategies, family support, etc. Some
people with mild learning disability do not receive health or social services.
The degree to which someone is disadvantaged or “handicapped” by a learning
disability therefore depends on social and cultural factors (and the nature of
any associated problems), and not just on the severity of their global cognitive
impairment.
Another
disadvantage of a label such as "learning disability" is that it
encompasses people with very different problems and needs. Some will have a
genetic or chromosomal disorder associated with particular physical (and
sometimes behavioural) problems. Others will only have learning problems. Some
have learning problems, but their quality of life is dependent on factors such
as the control of epileptic seizures rather than receipt of services to help
with learning problems. Labels such as learning disability (and diagnoses such
as autism or Down syndrome) are, however, helpful in many ways. They provide an
"explanation" of problems, may lessen feelings of guilt, may allow
appropriate services to be received, and may assist communication between
professionals.
HOW COMMON IS LEARNING DISABILITY?
The
frequency of occurrence of conditions among populations of people is often
described in terms of incidence (the number of people newly identified as having
a condition) or prevalence (the number of people identified as having the
condition at a particular time or over a defined length of time). For learning
disability, the incidence is often described for specific disorders (such as
Down syndrome) as the proportion of live born infants who have the condition.
The incidence of Down syndrome in the United Kingdom is around 1 in 500 live
born infants. However, such figures may be misleading, or not convey important
information. For example, almost all babies with Down syndrome are identified at
birth or shortly afterwards. Some other conditions (notably non-specific mild
learning disability) will not be detectable at birth, but may become apparent
during childhood. Similarly, the incidence of 1 in 500 live births for Down
syndrome is an average figure; the likelihood of having a baby with Down
syndrome rises with increasing maternal age and is about 1 in 32 for women who
are 45 years old (Udwin & Dennis, 1995).
Only
the most severe and obvious conditions, or those for which there is a screening
test, are detected at birth. The frequency of learning disability is therefore
usually described as a prevalence at a point in time for a defined group of
people. In spite of the difficulties (e.g. that mildly learning disabled people
may not be identified) there is reasonable agreement from studies in European
countries over the past 20 years that about 2% of the population have a mild
learning disability and about 0.35% of the population have a severe learning
disability (figures vary between about 2% and 3% for mild learning disability,
and 0.25% and 0.4% for severe learning disability). This roughly coincides with
the expected proportion of people with learning disability (i.e. an IQ less than
70) expected on the basis of the normal distribution of intelligence.
ASSOCIATED PROBLEMS
Problems
with learning are often not the most taxing difficulties faced by someone with a
"learning" disability. Conditions commonly associated with learning
disability include physical disabilities (especially neurological and
orthopaedic disorders), sensory impairments (visual or hearing impairments or
both), epilepsy (about a third of people with severe learning disability have
epilepsy, the proportion of people with seizures increasing with increasing
severity of learning disability), and psychiatric disorders (including mental
illness, behaviour disorders, autism and related conditions, and behaviours
associated with syndromal causes of disability). People with learning disability
are also vulnerable to medical problems such as thyroid disease and
gastrointestinal problems, but these vulnerabilities are much more pronounced in
some disorders than others. People with Down syndrome, for example, are
especially vulnerable to thyroid disease and are more likely than other people
to develop a dementia of Alzheimer type in middle age.
It is
important to be aware of the vulnerabilities associated with particular
conditions,
The
nature and severity of associated problems often determine the services that are
necessary to allow someone with learning disability to lead as normal a life as
possible. A careful balance may have to be struck between risks and benefits. In
the treatment of epilepsy, for example, some risk of seizures may be preferable
to unsteadiness or cognitive slowing resulting from high doses of anticonvulsant
medication. With the advent of newer anticonvulsant drugs, the benefit/risk
ratio is improving, but compromises and careful judgements will still be
necessary.
MULTI-AXIAL CLASSIFICATORY
SYSTEMS
Because
learning disability is often associated with physical or behavioural disorders,
a system of describing the diagnoses or problems faced by the individual is
often more appropriate than a single “diagnosis”.
Such a multi-axial system has been developed by the World Health
Organisation. It includes axes to describe:
The severity
of learning disability (“mental retardation” in ICD-10)
Physical
disorders (including the cause of the learning disability)
Psychiatric
and behavioural disorders
Impact of
disability on functioning
Psycho-social
factors (such as a history of abuse during childhood).
Although
designed primarily for use by mental health workers, such a system allows anyone
to structure their knowledge about a patient, client or resident and communicate
this knowledge to others in a succinct format.
Severity of
learning disability and associated problems.
Learning disability, associted IQ, approximate abilities
Mild 50 - 70
Hold conversation.
Moderate
35 - 50 Limited language.
Severe 20 - 35
Use of
words/gestures
Profound less than 20 Cannot understand
requests.
REFERENCES
Udwin, O.
& Dennis, J. (1995) Psychological and behavioural phenotypes in genetically
determined disorders: a review of research findings. In G. O’Brien & W.
Yule (eds) Behavioural Phenotypes. London: Mac Keith Press. World
Health Organization (1980) International Classification of Impairments, Disabilities, and Handicaps. A manual relating to the consequences of disease.
WHO:Geneva. World
Health Organization (1992) The ICD-10 Classification of Mental and FURTHER READING Harding, L.
& Beech, J.R. (eds) (1990) Testing people: a practical guide to
psychometrics. NFER-Nelson: Windsor.
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