Intellectual Disability 233assessment generates a useful profile of the child’s cognitive strengths
and weaknesses. For children and adolescents of school age, the Wechsler
Intelligence Scale for Children, fourth edition (WISC IV), or the British
Ability Scale, third edition (BAS3) provide a suitably wide-ranging battery
of verbal and visual spatial tests. The Vineland test of adaptive functioning
is a useful index of social functioning, particularly since there are extensive
population norms.
Diagnosis of the underlying cause of intellectual disability is based on:
1 a thorough history, with particular attention to family history, prenatal
infections and prenatal alcohol exposure;
2 a careful physical examination, particularly for neurological signs, dys-
morphic features and the skin signs of the neurocutaneous syndromes
(see Chapter 1);
3 selected special investigations, particularly for the fragile X syndrome,
chromosomal abnormalities and metabolic diseases.
Although very few treatable causes will be found, the search for a cause
is valuable for genetic counselling and because many parents are relieved
by a diagnostic label (partly because this opens the way to joining the
relevant parent self-help group). In Britain, diagnosis and counselling are
usually undertaken by paediatricians rather than psychiatrists.
Prevention of intellectual disability
Many approaches can reduce the prevalence of the organic syndromes
that sometimes or always result in intellectual disability. Thus, widespread
rubella vaccination can prevent congenital rubella. Neural tube defects
can be reduced by folic acid supplementation given around the time of
conception and in early pregnancy. Advice on alcohol consumption in
pregnancy can prevent the fetal alcohol syndrome. Prenatal diagnosis of
organic syndromes is increasingly possible on the basis of blood tests,
ultrasound scans, chorionic villous sampling and amniocentesis. Specific
treatments are rarely available, but parents may opt for termination
of pregnancy. Continuing advances in obstetric and neonatal care may
further reduce the rate of early brain damage, for example, by reduc-
ing the rate and complications of premature birth. Neonatal screening
for phenylketonuria, galactosaemia and hypothyroidism permits early
treatment before irreversible brain damage has occurred. Immunisation
can protect children against diseases that cause meningitis (for example,
Haemophilus influenzae type b) and encephalitis (for example, pertussis).
Measures to reduce the rate of domestic accidents, road traffic accidents
and physical abuse can reduce brain damage secondary to head injury.
Less progress has been made in reducing the rate of normal-variant
intellectual disability. Some interventions have targeted the infants of
mothers who themselves have an intellectual disability and live in socially
deprived neighbourhoods. These programmes can result in significant
increases in scholastic achievement and measured IQ, at least in the