skip to main content

Fragile X Syndrome — RACP Paediatrics MCQ

Instant feedback + full explanation. One question, done properly.

ModerateGenetics & MetabolicFragile X SyndromeRACP Paediatrics

A 5-year-old boy presents with a broad forehead, prominent jaw, large ears, macroorchidism, intellectual disability, and social anxiety. His maternal uncle has a similar phenotype. What is the most likely inheritance pattern and diagnosis?

Educational content. Not a substitute for clinical judgement or local policy.

Reveal the answer and explanation

Correct answer: D — X-linked dominant – Fragile X syndrome

Fragile X syndrome is the most common inherited cause of intellectual disability. It is caused by a CGG trinucleotide repeat expansion in the FMR1 gene on the X chromosome. Inheritance is X-linked dominant with reduced penetrance. Features include a long face, prominent ears, macroorchidism (post-pubertal), intellectual disability, ADHD, and autism spectrum features. Affected maternal uncles are a characteristic family pattern.

Reference: RACP – 2024 – Paediatric Curriculum: Clinical Genetics