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Foundation Sciences · Biochemistry

Homocysteine Metabolism

⏱️ 45–60 minutes read 📖 Biochemistry

Remethylation (B12/folate) and transsulphuration (B6, cystathionine β-synthase) pathways of homocysteine.

📌 Learning Objectives

  • Describe the key principles of homocysteine metabolism.
  • Explain the clinical relevance of homocysteine metabolism.
  • Recognise common conditions linked to homocysteine metabolism in MLA-style scenarios.

📋 Overview

Remethylation (B12/folate) and transsulphuration (B6, cystathionine β-synthase) pathways of homocysteine. This topic integrates with pathology, pharmacology and clinical medicine and is frequently tested in UK medical school exams and the MLA.

🔬 Basic Science

Remethylation (B12/folate) and transsulphuration (B6, cystathionine β-synthase) pathways of homocysteine. Detailed mechanisms, regulation and molecular interactions underpin both normal physiology and disease.

🏥 Clinical Relevance

Homocystinuria treated with B6, betaine, low-methionine diet.

🧪 Investigations

Relevant laboratory tests, imaging or histological examination are used as appropriate to the clinical context.

💊 Management

Management is condition-specific; principles include addressing the underlying biochemical/structural derangement, supportive care and targeted therapy where available.

Revision Resources – expand the sections below for high-yield notes, exam pearls, key facts and further reading.

🎯 MLA High-Yield Notes & Quick Revision ⌄
High-yield topic for the UK MLA — frequently appears in SBA questions linking biochemistry concepts to clinical presentations and management decisions.
Applying biomedical science to clinical practice Diagnosis and investigation Pathophysiology of common conditions
  • Remethylation (B12/folate) and transsulphuration (B6, cystathionine β-synthase) pathways of homocysteine.
⭐ Exam Pearls ⌄
⭐ High Yield
CBS deficiency → homocystinuria (Marfanoid, lens dislocation downward, thrombosis)
Hyperhomocysteinaemia is a CVD/VTE risk factor
Methionine synthase requires B12
💡 Clinical Pearl
: Homocystinuria treated with B6, betaine, low-methionine diet.
⚠️ Exam Tip — Common Mistakes
Confusing homocysteine metabolism with related but distinct mechanisms.
Memorising pathways without linking to clinical disease.
🔑 Key Facts ⌄
CBS deficiency → homocystinuria (Marfanoid, lens dislocation downward, thrombosis)
Hyperhomocysteinaemia is a CVD/VTE risk factor
Methionine synthase requires B12
📚 References ⌄
  1. BMJ Best Practice
  2. Robbins Basic Pathology
  3. Lippincott Illustrated Reviews: Biochemistry
  4. Wheater's Functional Histology
  5. NICE guidance where applicable.

Further Resources

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