What is Intellectual Disability?
Causes and Presentations
Dr Simon Bonell
Consultant Psychiatrist in Intellectual Disabilities
Plymouth Community Healthcare (CIC)
MRCPsych Course
Overview
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Definition of ID
Epidemiology of ID
Causes of ID
Cause of ID and relevance to psychiatric
disorders
Pathoplastic effect of ID on psychopathology
Assessment and diagnostic challenges
DC-LD approach to diagnosis
First a note on terminology
First a note on terminology
What is the definition of ID?
What is the definition of ID?
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Reduced level of intellectual functioning
Reduced ability to adapt to the daily
demands of a normal social
environment
Manifested during the developmental
period
How do you diagnose ID?
How do you diagnose ID?
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Clinical assessment
Adaptive behaviour
Psychometric test performance
Clinical assessment
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Developmental history
Family history
Childhood / educational history
Occupational history
Social history
Level of functioning
Past medical and psychiatric history
Forensic history
Pre-morbid personality
Clinical assessment
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Appearance and Behaviour
Speech
Mood
Thoughts
Perceptions
Cognition
Insight
The role of IQ
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Intelligence Quotient (IQ) measures a
range of different intellectual abilities
In most people skills develop to a
similar level
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Large discrepancies can occur esp. in ID
IQ scores summated to give verbal and
performance score and a full scale IQ
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Normal distribution
The role of IQ
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Mean IQ of population is 100
IQ of 70 represents 2 standard
deviations from the mean
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Mild ID: 50 – 69
Moderate ID: 35 – 49
Severe ID: 20 – 34
Profound ID: <20
Epidemiology
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2.27% of the population have IQ<70
Add those with specific causes
Overall prevalence rate between 2 – 3%
75 – 90% have mild ID
A note on “mental age”
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Adult with profound ID has an
equivalent mental age of 0 – 3 years
Unable to understand abstract concepts
However, has lifelong experiences, skills
development and adult biological urges
and drives
“Mental age” should not be used for
adults
Clinical descriptors of ID
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Mild ID
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The majority of people with ID
Verbal communication usually reasonable but note
receptive / expressive mismatch and
overestimation of understanding and abilities
Usually only minimal support with basic self care
but some deficits in more complex aspects of
social functioning (finance / employment)
Support level ranges from none to very high levels
(if significant risks are present)
Clinical descriptors of ID
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Moderate ID
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Verbal communication more reduced. Can
generally understand short simple
sentences
Higher levels of support with self care
usually required. Difficulties in adapting to
new situations (e.g. may learn to use a bus
independently but not able to work out a
new route)
Moderate to high levels of support required
Clinical descriptors of ID
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Severe / profound ID
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Little expressive verbal ability but note
understanding may be better
Needs high levels of support with basic self
care
Increasing rates of sensory deficits and
physical disabilities
Why do we label a group of
people as having “ID”
Vulnerability
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To mental illness
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40% of people with ID have “mental
disorder”
To physical illness
To poor treatment by society
Causes of ID
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“Idiopathic” ID accounts for 30 – 50%
of cases
Most common inherited cause of ID:
Fragile X
Most common chromosomal defect:
Down Syndrome
Why is the cause of ID relevant to the
psychiatrist?
Behavioural phenotypes
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Prader-Willi:
Lesch-Nyhan:
Smith-Magenis:
22q11.2 deletion
Rett:
Angelman:
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5p- (Cri du chat):
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Hyperphagia, food ideation
Extreme self mutilation
Objects in orifices, self hugging
Psychotic illness
Stereotypic hand movements
Puppet-like gait, attraction to
water
Inappropriate laughter, cat-cry
during infancy
Causes of ID
Prenatal
Inherited disorders (such as phenylketonuria,
Tay-Sachs disease, neurofibromatosis, tuberous
sclerosis, hypothyroidism, and fragile X
syndrome)
Chromosome abnormalities – Down syndrome
[Trisomy 21, mosaic, translocation], PraderWilli, Klinefelter’s syndrome, Cri-du-chat etc
Causes of ID
Intra-uterine
Severe maternal malnutrition
Infections (HIV, cytomegalovirus, herpes simplex,
toxoplasmosis, rubella virus)
Toxins (such as alcohol, lead, and mercury)
Drugs (such as phenytoin, valproate, chemotherapy)
Abnormal brain development (such as porencephalic cyst,
grey matter heterotopia, hydrocephalus, neural tube
defects and encephalocele)
Pre-eclampsia and multiple births
Placental dysfunction (IUGR, toxaemia)
Causes of ID
Perinatal
Birth asphyxia/Hypoxic brain damage
Extreme prematurity
Kernicterus
Causes of ID
Postnatal
Brain infections (such as meningitis and
encephalitis)
Severe head injury
Malnutrition of the child
Severe emotional neglect or abuse
Toxins (such as lead and mercury)
Brain tumours and their treatments
Down Syndrome
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Trisomy 21
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95% caused by non-disjunction
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2-3% Robertsonian translocation
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88% maternal non-disjunction
Long arm chromosome 21 attached to chromosome 14
Not linked to maternal age
1-2% Mosaic
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Some cells have normal karyotype and others have
trisomy 21
Down Syndrome
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Typical physical appearance
Congenital heart disease
Haematological malignancies
Thyroid disorder
Eye and hearing disorders
Gastrointestinal abnormalities
Average IQ 50
Down Syndrome
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Increased risk of Alzheimer’s type
dementia
Increased risk of autism
Possible increased risk of depressive
disorder
Conduct disorder in childhood
Prader Willi syndrome
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Results from failure of expression of
paternally derived gene on chromosome
15
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15q11-13
Failure of maternally derived gene leads
to Angelman syndrome
PWS genetics
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Interstitial deletions
70%
Uniparental disomy
25%
Imprinting centre
defects <5%
Chromosomal
translocations 1%
Clinical features
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Infant
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Lethargy
Hypotonia
Poor feeding / failure to thrive
Childhood
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Short stature
Hypogonadism
Hyperphagia and obesity
Clinical features
Psychosis and PWS
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Case reports of cyclic affective disorders
and psychosis
Boer et al (2002) Lancet
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Identified all people with PWS in
Oxford/Anglia
25 adults with genetic confirmation of PWS
15 had detailed psychiatric assessment
Psychosis and PWS
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Boer 2002
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28% of adults with PWS have severe affective disorder +
psychotic symptoms
8% of adults with deletion
62% of adults with uniparental disomy
Later study (Soni 2007)
Psychotic illness
BPAD with psychotic
symptoms
Psychotic depression
Non-psychotic depression
0
5
10
15
20
25
30
35
40
45
50
mUPD
Deletion
Medication in PWS
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Those on antipsychotic or
antidepressant medication significantly
less likely to have relapse
Those on mood stabilising medication
more likely to have a relapse
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Sodium valproate & carbamazepine may
not be effective for people with PWS
Mood stabilisers only used in more severe,
relapsing conditions (BPAD)
Diagnostic and Assessment
Issues in ID
Diagnostic Challenges in ID
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ICD-10 assumes a certain level of
cognitive / verbal ability
Level of ID important in assessment of
possible mental health problems
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Short, simple questions
Risk of suggestibility
Repeat and check answers
Use time anchors
Diagnostic challenges in ID
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Same range of psychopathology is not
experienced in people with ID as
general population
ICD/DCM weighted heavily towards
verbal items and intellectually complex
concepts (guilt, body image etc.)
Diagnostic Challenges in ID
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Darren is a 35 year old man with severe
intellectual disability and longstanding
self-injurious behaviour (hand biting
and banging his head against walls). He
is taken to the GP due to increased self
injurious behaviour. The GP starts
risperidone and refers him to the LD
psychiatrist due to his behaviour.
Diagnostic Challenges
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Diagnostic overshadowing:- behaviour /
presentation is attributed to ID rather than a
diagnosable condition
Baseline exaggeration :- high levels of
unusual behaviour prior to the onset of a
condition make it difficult to recognise the
onset of a new disorder
Loss of skills and impairment of
communication may also be signs of mental
illness
Diagnostic Challenges in ID
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Mike is a 48 year old man with
moderate learning disabilities. He is
referred to the psychiatrist after being
seen outside his new home waving at
passing cars and making gestures. His
support staff are concerned about him
talking to himself and think he might
have developed psychosis.
Impact of ID on MH
presentations
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Psychosocial masking
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Cognitive disintegration
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Impoverished social skills and life experiences result in
unsophisticated presentation of a disorder or misdiagnosis of
unusual behaviour as a psychiatric disorder
Decreased ability to tolerate stress leading to anxietyinduced decompensation (often misdiagnosed as a psychotic
illness)
Misdiagnosis of developmentally appropriate
phenomenon
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Developmentally appropriate behaviours that are
inappropriate for chronological age are misdiagnosed as
psychiatric disorder (solitary play, talking to oneself and
imaginary friends taken as evidence of psychosis)
Impact of functional impairment
on mental health presentations
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Implications for mental state examination
Assessment of decline in abilities
Working with carers
Sensory impairments
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Common (deafness 40 x more common and
blindness 8.5 x more common than general
population)
Diagnostic classificatory systems
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DC-LD
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Provides operationalised diagnostic criteria
for psychiatric disorders in people with ID
Works in a complementary way with ICD-10
Developed by the RCPsych
Hierarchical system to reach diagnoses
DC-LD
Axis I
Axis II
Axis III
Level
Level
Level
Level
Level
Level of ID
Cause of ID
Psychiatric disorders
A
B
C
D
E
Developmental disorders
Psychiatric illnesses
Personality disorders
Problem behaviours
Other disorders
Example of DC-LD hierarchical
approach
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Jane is a 24 year old lady with
moderate ID and excessive over eating
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Use the hierarchical approach to consider
the differential diagnosis
Example of DC-LD hierarchical
approach
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Jane is a 24 year old lady with moderate ID and
excessive over eating
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Axis I: level of ID does not account for the over eating
Axis II: ascertain cause of ID. If Prader-Willi syndrome present
then eating a feature of this. If not continue to Axis III
Axis III:
Level A: does Jane have a developmental disorder? Eg. is the
over-eating a ritual associated with autism?
Level B: is there evidence of a psychiatric illness (e.g.
depression or an eating disorder)
Level C: is a personality disorder present? Does this account for
her over-eating?
Summary
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ID is defined as a significant impairment in cognitive
abilities and adaptive social functioning that arises
during the developmental period
Increased risk of physical and mental disorders
The cause of ID can shed light on MH presentation
Assessment must include consideration of the
biological, psychological, social and developmental
issues
The DC-LD provides a hierarchical structure to reach
psychiatric diagnoses in people with ID
Reading
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Books
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Intellectual Disability Psychiatry: a practical
handbook 2009 Eds Hassiotis, Barron & Hall
DC-LD 2001 Royal College of Psychiatrists
Psychiatric and Behavioural Disorders in
Intellectual and Developmental Disabilities 2007
Eds Bouras and Holt
Intellectual Disability and Ill Health 2010 Eds.
O’Hara, McCarthy and Bouras
Reading
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Papers
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Cooper et al (2007) Mental ill-health in adults with
intellectual disabilities: prevalence and associated
factors BJPsych
Boer et al (2002) Psychotic illness in people with
Prader Willi syndrome due to chromosome 15
maternal uniparental disomy The Lancet 350
Soni et al (2007) The course and outcome of
psychiatric illness in people with Prader–Willi
syndrome: implications for management and
treatment JIDR 51
Questions
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Email: s.bonell@nhs.net