Intellectual disability - Burton

Question 1

What is the ICD-10 definition of intellectual disability (mental retardation)?

Answer 1

A condition of arrested or incomplete development of the mind, which is especially characterised by impairment of skills manifested during the developmental period, skills which contribute to the overall level of intelligence, i.e. cognitive, language, motor, and social abilities.

Question 2

What three things does the DSM-IV stipulate are required to diagnose intellectual disability?

Answer 2

1. IQ of 70 or less
2. Significant limitations in adaptive functioning in at least two areas
3. Onset before the age of 18

Question 3

What are the four subtypes of intellectual disability?

Answer 3

Mild (85% of cases)
Moderate (10%)
Severe and Profound (5%)

Question 4

What is mild intellectual disability?

Answer 4

Needs only limited assistance and support
Can otherwise become self-sufficient and live independently
IQ 69-50

Question 5

What is moderate intellectual disability?

Answer 5

Needs variable degrees of assistance or support
Can live in a supervised environment such as a group home, and work in a sheltered workshop
IQ 49-35

Question 6

What is severe intellectual disability?

Answer 6

CAn master basic self-care and communication skills, but nonetheless needs continuous care
IQ 34-20

Question 7

What is profound intellectual disability?

Answer 7

Not capable of self-care, needs continuous care.

IQ <20

Question 8

What is the prevalence of intellectual disability?

Answer 8

2-3%

Question 9

What are some common specific causes of intellectual disability?

Answer 9

Genetics
Pre-natal
Peri-natal
Post-natal

Question 10

What are the pre-natal causes of ID?

Answer 10

Pre-eclampsia
Placental insufficiency
Hydrocephalus
Myelomeningocoele 
Congenital hypothyroidism
Infection (rubella, toxoplasmosis, cytomegalovirus, syphilis, HIV
Foetal alcohol syndrome

Question 11

What are the peri-natal causes of ID?

Answer 11

Brain trauma and hypoxia
Intraventricular haemorrhage
Hyperbilirubinaemia
Infections

Question 12

What are the post-natal causes of ID?

Answer 12

Head injury
Brain infections
Brain tumours
Hypoxia
Chronic lead poisoning
Neglect and abuse
Malnutrition and general poverty

Question 13

What are the genetic causes of ID?

Answer 13

Trisomy 21 (Down's syndrome)
Fragile X syndrome (Martin-Bell syndrome)
Other chromosomal abnormalities
Single gene disorders (phenylketonuria)
Other metabolic disorders
Neurofibromatosis 
Tuberous sclerosis

Question 14

What is the most common and second most common cause of ID and what is its incidence?

Answer 14

Most common:
Down’s syndrome
1 in 700 births

Second most common:
Fragile X syndrome
1 in 1500 births

Question 15

What are the causes of Down’s syndrome and what percentage do they cause?

Answer 15

Trisomy 21 (95%)
Robertsonian translocations (4%)
Mosaicism (1%)

Question 16

What are the physical abnormalities of Down’s syndrome?

Answer 16

Oblique or almond-shaped palpebral fissures
Brushfield spots on the irises
Flat nasal bridge
Protruding tongue
Short neck and shortened limbs
Single transverse palmar creases

Question 17

What risk factors are associated with Down’s syndrome?

Answer 17

Deafness
Cataracts
Respiratory infections
Cardiovascular malformations
GI abnormalities
Haematological abnormalities
Hypothyroidism
Epilepsy
Early onset Alzheimer's disease

Question 18

What is the cause of fragile X syndrome?

Answer 18

CGG trinucleotide repeats in the FMR1 gene on the long arm of chromosome X, so commoner in males

Question 19

What are the physical abnormalities of fragile X syndrome?

Answer 19

Elongated face
Large or protruding ears
Prognathism (extension of jaw)
Macro-orchidism
Hypotonia

Question 20

What do all trinucleotide repeat disorders (Huntington’s, Lesch Nyhan…) have in common?

Answer 20

Anticipation (disease severity increases in successive generations)

Question 21

What is the most common metabolic disorder?

Answer 21

Phenylketonuria

1 in 10000 births

Question 22

What is the pathophysiology of phenylketonuria?

Answer 22

Autosomal recessive inheritance of a defect in the phenylalanine hydroxylase enzyme results in a high serum phenylalanine.

Question 23

What are the physical abnormalities of phenylketonuria?

What is the treatment?

Answer 23

Short stature
Hyperactivity
Irritability
Epilepsy
Lack of pigment
Eczema

Diet control (avoid protein rich foods; eggs, milk etc)

Question 24

Mental disorders are all more common in ID than in the normal population: how could schizophrenia present in ID?

Answer 24

Deterioration from previous level of functioning
Behaviour that seems out of character
Indirect evidence of hallucinations and delusions

Question 25

How could hypomania present in ID?

Answer 25

Giggling
Overactivity
Disinhibition

Question 26

How could depressions present in ID?

Answer 26

Loss of appetite
Sleep disturbance
Speech and motor retardation
Anhedonia