Haemophilia A inheritance — MRCPCH TAS MCQ

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ModerateGeneticsHaemophilia A inheritanceMRCPCH TAS

A 10-month-old boy has extensive bruising after immunisation. APTT is prolonged, PT is normal and factor VIII activity is very low. His maternal grandfather had a bleeding disorder. What is the most likely inheritance pattern?

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Correct answer: A — X-linked recessive

Haemophilia A is usually X-linked recessive, producing affected males and carrier females in the maternal line. Autosomal recessive bleeding disorders affect males and females more equally and may be associated with consanguinity. The pearl is that an isolated prolonged APTT with normal PT points towards intrinsic pathway factor deficiency.

Reference: Nelson Textbook of Pediatrics; RCPCH Theory examination syllabi; Lissauer's Illustrated Textbook of Paediatrics