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Language in genetic syndromes, intellectual disability and selective mutism
In intellectual disability language develops in the usual order but slowly, and each syndrome creates its own profile — in Down syndrome syntactic expression is weaker than comprehension, in Williams syndrome vocabulary and social drive are relatively strong — while selective mutism is an anxiety disorder in which the child speaks at home and is silent elsewhere.
Why it matters in the exam
Exam questions ask you to match a profile to a syndrome: what will be hard for a child with Down syndrome (producing a long noun phrase with an embedded clause); what characterises a child with Williams syndrome (good vocabulary and social drive, with visuospatial difficulty); and which of the syndromes once grouped under "pervasive developmental disorders" has a known genetic basis (Rett). You are also asked that in mild to moderate intellectual disability language develops in the usual order, more slowly, and that different syndromes affect language in different ways.
Selective mutism is presented as a preschool girl whose home videos show normal, fluent talk, while at kindergarten she has stayed silent for many months, even with staff she knows. The diagnosis is selective mutism, and treatment is team-based with gradual exposure. For differential diagnosis you may also be asked about an 18-month-old who does not respond to speech: think of severe hearing loss and of autism.
Key points
- Intellectual disability: same order, slow pace, profile by syndrome.
- Down syndrome: weak expression and syntax; hearing checks.
- Williams syndrome: strong words and social drive, weak visuospatial skills.
- Rett syndrome: regression and hand movements; a known genetic basis.
- Selective mutism: anxiety, normal language, gradual exposure.
Summary table
| Condition | Language and communication profile | Exam point |
|---|---|---|
| Mild to moderate intellectual disability | The usual order of acquisition, but slow | The profile depends on the syndrome |
| Down syndrome | Expression and syntax weaker than comprehension and vocabulary; low intelligibility; hypotonia | High rate of middle ear fluid — check hearing |
| Williams syndrome | Good vocabulary and strong social drive, visuospatial difficulty | A profile "opposite" to Down syndrome in some areas |
| Fragile X syndrome | Perseveration, fast disorganised speech, gaze avoidance, social anxiety | More common in boys |
| Rett syndrome | Regression in communication and hand use, repetitive hand movements | A known genetic basis (MECP2), mainly in girls |
| Selective mutism | Speaks freely in one place and is silent in others over time, normal language | An anxiety disorder; team and gradual exposure |
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Sources
- Abbeduto, Warren & Conners, Mental Retardation and Developmental Disabilities Research Reviews, 2007 — Language development in Down syndrome
- Mervis & John, American Journal of Medical Genetics, 2010 — Cognitive and behavioural characteristics of Williams syndrome
- American Psychiatric Association, DSM-5, 2013 — Selective mutism
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-02. The text may contain errors; when in doubt, check the source.