Genetic causes of DD/ID

 

Chromosomal conditions

(see Chromosomal conditions)

  1. Aneuploidy, eg trisomy 21 (Down syndrome)
  2. Chromosome deletion syndromes, eg Wolf-Hirschhorn syndrome, 5p- syndrome (Cri-du-chat syndrome)
  3. Chromosome microdeletion syndromes, eg Williams syndrome, Prader-Willi syndrome, Angelman syndrome
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Single gene conditions

  1. Autosomal dominant inheritance, eg tuberous sclerosis
  2. Autosomal recessive inheritance, eg metabolic conditions, including phenylketonuria (PKU)
    (see Newborn screening)
  3. X-linked inheritance, eg fragile X syndrome, Rett syndrome, X-linked lissencephaly, ARX gene mutations
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Congenital infections/ teratogens

  1. Congenital cytomegalovirus, congenital HIV
  2. Fetal alcohol syndrome
  3. Fetal anticonvulsant syndrome
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Individuals with conditions that can cause developmental delay
may present at different ages:

 

Prenatally

  1. Detected by ultrasound, eg fetal brain abnormality
  2. Detected by chorionic villus sampling or amniocentesis, eg Down syndrome (see Testing and
    pregnancy    )
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At birth or during the neonatal period

  1. Dysmorphic features/birth defects, eg many chromosomal conditions or genetic syndromes
  2. Neurological abnormality, eg hypotonia in Prader-Willi syndrome
  3. Identified by newborn screening, eg PKU (see Newborn screening)
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In infancy

  1. Marked delays, eg congenital brain malformations, Rett syndrome
  2. Regression in psychomotor skills
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During early childhood

  1. Mild/moderate ID/DD with speech or language delay and/or behavioural difficulties, eg fragile X syndrome, Williams syndrome
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During school age years

  1. Learning/socialisation problems
  2. Mild ID or borderline ability or specific learning disability, eg velocardiofacial syndrome with 22q11 deletion
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