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Fragile X Inheritance — RACP Paediatrics MCQ

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ModerateGenetics & MetabolicFragile X InheritanceRACP Paediatrics

A 5-year-old boy has intellectual disability, macroorchidism, a long face with prominent ears, and a family history of intellectual disability in maternal uncles. What is the inheritance pattern?

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Correct answer: E — X-linked dominant (with variable expressivity in females)

Fragile X syndrome (FMR1 trinucleotide CGG repeat expansion) is X-linked dominant with variable expressivity. Males are typically more severely affected. Carrier females may have mild cognitive difficulties. Premutation carriers are at risk of FXTAS (tremor/ataxia) and premature ovarian insufficiency.

Reference: RACP – 2024 – Paediatric Curriculum: Clinical Genetics