Fragile X Syndrome

⏱️ 30 mins read 📖 Genetics 🎯 MLA Relevance: High

Fragile X syndrome is the commonest inherited cause of intellectual disability, caused by CGG trinucleotide repeat expansion in FMR1 on the X chromosome.

📌 Learning Objectives

Describe the underlying mechanism of Fragile X Syndrome.
Identify the key clinical features and complications of Fragile X Syndrome.
Outline the appropriate investigations and management of Fragile X Syndrome.
Discuss the implications for patients and families of Fragile X Syndrome.

📋 Overview

Features include intellectual disability, long face, large ears, macroorchidism (post-pubertal), autism spectrum features and joint hypermobility. Premutation carriers may develop FXTAS or POI.

🔬 Basic Science

Features include intellectual disability, long face, large ears, macroorchidism (post-pubertal), autism spectrum features and joint hypermobility. Premutation carriers may develop FXTAS or POI.

🏥 Clinical Relevance

Genetic counselling is essential for premutation carriers.

🧪 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.

fragile x fmr1 cgg repeat fxtas fxpoi

Fragile X is due to CGG repeat expansion in the FMR1 gene (>200 = full mutation).
It is the commonest inherited cause of intellectual disability.
Premutation females may develop primary ovarian insufficiency (FXPOI).
Premutation males may develop fragile X tremor/ataxia syndrome (FXTAS).
Anticipation occurs through the maternal line.

⭐ Exam Pearls ⌄

⭐ High Yield

Fragile X is due to CGG repeat expansion in the FMR1 gene (>200 = full mutation).

It is the commonest inherited cause of intellectual disability.

Premutation females may develop primary ovarian insufficiency (FXPOI).

Premutation males may develop fragile X tremor/ataxia syndrome (FXTAS).

Anticipation occurs through the maternal line.

💡 Clinical Pearl

Fragile X: Genetic counselling is essential for premutation carriers.

⚠️ Exam Tip — Common Mistakes

Confusing the mechanism of Fragile X Syndrome with related conditions.

Missing classic clinical features of Fragile X Syndrome in SBA stems.

Failing to consider Fragile X Syndrome in the differential diagnosis.

🔑 Key Facts ⌄

Fragile X is due to CGG repeat expansion in the FMR1 gene (>200 = full mutation).

It is the commonest inherited cause of intellectual disability.

Premutation females may develop primary ovarian insufficiency (FXPOI).

Premutation males may develop fragile X tremor/ataxia syndrome (FXTAS).

Anticipation occurs through the maternal line.

🔗 Related Topics ⌄

📚 References ⌄

GMC MLA Content Map
NICE Clinical Knowledge Summaries
BMJ Best Practice

Further Resources

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