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Foundation Sciences · Genetics
Down Syndrome (Trisomy 21)
Down syndrome is caused by an extra copy of chromosome 21 (95% free trisomy, 4% translocation, 1% mosaic) and is the commonest autosomal aneuploidy.
📌 Learning Objectives
- Describe the underlying mechanism of Down Syndrome (Trisomy 21).
- Identify the key clinical features and complications of Down Syndrome (Trisomy 21).
- Outline the appropriate investigations and management of Down Syndrome (Trisomy 21).
- Discuss the implications for patients and families of Down Syndrome (Trisomy 21).
📋 Overview
Features include characteristic facies, hypotonia, single palmar crease, congenital heart defects (especially AVSD), duodenal atresia, hypothyroidism, leukaemia risk and Alzheimer disease in later life.
🔬 Basic Science
Features include characteristic facies, hypotonia, single palmar crease, congenital heart defects (especially AVSD), duodenal atresia, hypothyroidism, leukaemia risk and Alzheimer disease in later life.
🏥 Clinical Relevance
Lifelong multidisciplinary care includes screening for cardiac, thyroid, hearing, vision and haematological complications.
🧪 Investigations
Investigation depends on clinical context: relevant blood tests, imaging, and specific genetic or histopathological tests as appropriate. Refer to specialist services where indicated.
💊 Management
Management is condition-specific and typically multidisciplinary, combining medical therapy, surgical intervention where appropriate, supportive care, and family/genetic counselling.
Revision Resources – expand the sections below for high-yield notes, exam pearls, key facts and further reading.
MLA High-Yield Notes & Quick Revision ⌄
Common SBA themes: recognising the underlying mechanism, identifying classic clinical features, and choosing the first-line investigation or management step. Watch for inheritance pattern and characteristic associations.
down syndrome
trisomy 21
avsd
duodenal atresia
nipt
- 95% of Down syndrome is due to free trisomy 21 from maternal meiosis I non-disjunction.
- AVSD is the most characteristic congenital heart defect in Down syndrome.
- Duodenal atresia ('double-bubble' on AXR) is more common in Down syndrome.
- Annual TFTs are recommended due to high hypothyroidism risk.
- Adults with Down syndrome have markedly increased risk of early Alzheimer disease.
Exam Pearls ⌄
⭐ High Yield
95% of Down syndrome is due to free trisomy 21 from maternal meiosis I non-disjunction.
AVSD is the most characteristic congenital heart defect in Down syndrome.
Duodenal atresia ('double-bubble' on AXR) is more common in Down syndrome.
Annual TFTs are recommended due to high hypothyroidism risk.
Adults with Down syndrome have markedly increased risk of early Alzheimer disease.
💡 Clinical Pearl
Down Syndrome: Lifelong multidisciplinary care includes screening for cardiac, thyroid, hearing, vision and haematological complications.
⚠️ Exam Tip — Common Mistakes
Confusing the mechanism of Down Syndrome (Trisomy 21) with related conditions.
Missing classic clinical features of Down Syndrome (Trisomy 21) in SBA stems.
Failing to consider Down Syndrome (Trisomy 21) in the differential diagnosis.
Key Facts ⌄
95% of Down syndrome is due to free trisomy 21 from maternal meiosis I non-disjunction.
AVSD is the most characteristic congenital heart defect in Down syndrome.
Duodenal atresia ('double-bubble' on AXR) is more common in Down syndrome.
Annual TFTs are recommended due to high hypothyroidism risk.
Adults with Down syndrome have markedly increased risk of early Alzheimer disease.
Related Topics ⌄
References ⌄
- GMC MLA Content Map
- NICE Clinical Knowledge Summaries
- BMJ Best Practice
Further Resources
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