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Prompt
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Stem
A 4-year-old from a consanguineous family burns severely after minutes outdoors. Exposed skin shows dense freckling and poikiloderma; covered skin is relatively spared. There is photophobia. An older cousin died of metastatic skin cancer in adolescence.
Questions
a) What is the most likely diagnosis and the core molecular mechanism? (2 marks)
b) How are complementation groups organised, and which clinical axes differ between groups? (3 marks)
c) Detail lifelong management including photoprotection, surveillance, and multi-disciplinary care. (3 marks)
d) What genetic counselling points and differential diagnoses must you cover? (2 marks)
Model outline
- a) XP; defective NER of UV photoproducts (or POLH in XP-V).
- b) XPA–G NER steps; XP-V POLH; skin-cancer vs neurologic predominance varies (e.g. XPA neuro, XPC/XP-V skin-predominant).
- c) SPF50+/UPF/eyewear/window films; frequent skin checks; early excision/Mohs; ophthalmology; neurology if indicated; vitamin D; adherence support.
- d) AR 25% recurrence; cascade testing; differentiate Cockayne, TTD, porphyria, albinism.