Table 5 Some microdeletion and microduplication syndromes
SyndromeChromosomal location and key genes (if identified)Typical size of deletion/duplicationEstimated incidence among live-birthsTypical phenotypic features (not exhaustive, and not all these features are seen in all cases)
Di George syndrome/22q11 deletion syndrome22q11.2
TBX1, COMT
3 Mb deletion (90% of cases)1/4000Congenital heart defects, cleft palate, developmental delay, learning difficulty, increased risk of mental illness, recurrent infections
Williams syndrome/Williams–Beuren syndrome7q11.3
CLIP2, ELN, GTF2I, GTF2IRD1, LIMK1
1.5–1.8 Mb deletion1/7500 to 1/10000Supravalvular aortic stenosis, joint problems and loose skin, mild to moderate intellectual disability, characteristic ‘elfin’ facial appearance
Smith–Magenis syndrome17p11.2
RAI1
Approximately 3.6 Mb deletion1/15000 to 1/25000Mild to moderate intellectual disability, disturbed sleep patterns, behaviour problems including aggression and self-harm
Cri-du-chat syndrome5p15.2
CTNND2
Approximately 5–40 Mb deletion1/15000 to 1/50000Cat-like cry, microcephaly, severe psychomotor problems and severe intellectual disability
Wolf–Hirschhorn syndrome4p16.3
NSD2, LETM1, MSX1
Approximately 5–18 Mb deletion1/50000Characteristic ‘Greek warrior helmet’ facial appearance, delayed growth and development, mild to severe intellectual disability
Potocki–Lupski syndrome17p11.2
RAI1
Approximately 3.6 Mb duplication1/25000Developmental delay, mild to moderate learning disability, behavioural problems
Cat eye syndrome/Schmid–Fraccaro syndrome22q11
ADA2, CECR2
2–5 Mb duplication or triplication1/50000 to 1/150000Preauricular skin tags or pits, ocular coloboma, anal atresia with fistula, heart and renal malformations
  • Where specific genes have been identified as associated with particular features of the syndrome these are noted, but this does not exclude a role for additional genes in the region. Extent of the deletions/duplications often varies between patients but in general larger imbalances are associated with greater severity of symptoms.