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Foundation Sciences · Genetics

Trinucleotide Repeat Disorders

⏱️ 30 mins read 📖 Genetics 🎯 MLA Relevance: High

Trinucleotide repeat disorders are caused by unstable expansion of repeat sequences and often show anticipation (worsening with each generation).

📌 Learning Objectives

  • Describe the underlying mechanism of Trinucleotide Repeat Disorders.
  • Identify the key clinical features and complications of Trinucleotide Repeat Disorders.
  • Outline the appropriate investigations and management of Trinucleotide Repeat Disorders.
  • Discuss the implications for patients and families of Trinucleotide Repeat Disorders.
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Curriculum Mapped
UK MLA Curriculum

📋 Overview

Examples include Huntington disease (CAG in HTT), myotonic dystrophy (CTG in DMPK), Fragile X (CGG in FMR1) and Friedreich ataxia (GAA in FXN).

🔬 Basic Science

Examples include Huntington disease (CAG in HTT), myotonic dystrophy (CTG in DMPK), Fragile X (CGG in FMR1) and Friedreich ataxia (GAA in FXN).

🏥 Clinical Relevance

Predictive testing in autosomal dominant adult-onset conditions like HD requires careful genetic counselling.

🧪 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.
trinucleotide repeat anticipation huntington myotonic dystrophy friedreich
  • Huntington disease: CAG repeats in HTT (autosomal dominant, anticipation via father).
  • Myotonic dystrophy: CTG repeats in DMPK (autosomal dominant, anticipation via mother).
  • Fragile X: CGG repeats in FMR1 (X-linked).
  • Friedreich ataxia: GAA repeats in FXN (autosomal recessive).
  • Anticipation involves earlier onset and increased severity in successive generations.
⭐ Exam Pearls ⌄
⭐ High Yield
Huntington disease: CAG repeats in HTT (autosomal dominant, anticipation via father).
Myotonic dystrophy: CTG repeats in DMPK (autosomal dominant, anticipation via mother).
Fragile X: CGG repeats in FMR1 (X-linked).
Friedreich ataxia: GAA repeats in FXN (autosomal recessive).
Anticipation involves earlier onset and increased severity in successive generations.
💡 Clinical Pearl
Trinucleotide Repeat: Predictive testing in autosomal dominant adult-onset conditions like HD requires careful genetic counselling.
⚠️ Exam Tip — Common Mistakes
Confusing the mechanism of Trinucleotide Repeat Disorders with related conditions.
Missing classic clinical features of Trinucleotide Repeat Disorders in SBA stems.
Failing to consider Trinucleotide Repeat Disorders in the differential diagnosis.
🔑 Key Facts ⌄
Huntington disease: CAG repeats in HTT (autosomal dominant, anticipation via father).
Myotonic dystrophy: CTG repeats in DMPK (autosomal dominant, anticipation via mother).
Fragile X: CGG repeats in FMR1 (X-linked).
Friedreich ataxia: GAA repeats in FXN (autosomal recessive).
Anticipation involves earlier onset and increased severity in successive generations.
🔗 Related Topics ⌄
🔬 Fragile X Syndrome Foundation Sciences → 🔬 Huntington Disease Foundation Sciences → 🔬 Autosomal Dominant Disorders Foundation Sciences →
📚 References ⌄
  1. GMC MLA Content Map
  2. NICE Clinical Knowledge Summaries
  3. BMJ Best Practice

Further Resources

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