Paper I
Question
Morphologic features in Trisomy 21
Answer
Trisomy 21 (Down syndrome) results from an extra copy of chromosome 21.
Craniofacial features
- Flat facial profile with a small nose and flat nasal bridge
- Upward slanting (oblique) palpebral fissures
- Epicanthic folds
- Brushfield spots (speckled iris)
- Small, low-set ears
- Protruding tongue (relative macroglossia) with an open mouth
- Small head (microcephaly) with a flat occiput (brachycephaly)
Limb/hand features
- Single transverse palmar crease (simian crease)
- Short, broad hands with a short, incurved fifth finger (clinodactyly)
- Wide gap between the first and second toes (“sandal gap”)
- Hypotonia (generalized poor muscle tone)
Systemic associations
- Congenital heart defects (most commonly atrioventricular septal defect) — present in about 40% of cases
- Duodenal atresia/other GI malformations
- Increased risk of acute leukaemia (both ALL and AML, including transient myeloproliferative disorder in neonates)
- Early-onset Alzheimer disease (due to triplication of the APP gene on chromosome 21)
- Intellectual disability
- Increased susceptibility to infections (immune dysfunction)
- Hypothyroidism