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ABD Photodermatology and UV Effects Flashcards

6 cards from real ABD practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

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  1. Porphyria cutanea tarda (PCT) is caused by deficiency of which enzyme in the heme biosynthesis pathway?

    Answer: Uroporphyrinogen decarboxylase (UROD)

    PCT results from deficiency of uroporphyrinogen decarboxylase (UROD), causing accumulation of uroporphyrins that absorb light and generate reactive oxygen species in the skin.

  2. Erythropoietic protoporphyria (EPP), the most painful photosensitivity disorder, is classically caused by mutations in which gene?

    Answer: FECH (ferrochelatase)

    Classic autosomal recessive EPP is caused by loss-of-function mutations in FECH (ferrochelatase), the terminal enzyme of heme synthesis, causing protoporphyrin IX accumulation.

  3. Which SPF value blocks approximately 97% of UVB radiation?

    Answer: SPF 30

    SPF 30 blocks approximately 97% of UVB radiation; SPF 15 blocks 93%, SPF 50 blocks 98%, and SPF 100 blocks 99%, showing diminishing returns at higher values.

  4. Chronic actinic dermatitis (CAD) is characterized by which predominant lymphocyte subset on histopathology?

    Answer: CD8+ cytotoxic T cells

    CAD characteristically shows a CD8+ cytotoxic T-cell predominant infiltrate, which distinguishes it from other eczematous dermatoses that are predominantly CD4+.

  5. UVB radiation (280-315nm) is primarily responsible for photocarcinogenesis through which mechanism?

    Answer: Direct DNA damage forming cyclobutane pyrimidine dimers (CPDs) and 6-4 photoproducts

    UVB causes direct DNA damage by forming cyclobutane pyrimidine dimers (CPDs) and 6-4 photoproducts between adjacent pyrimidines, producing C→T transition mutations.

  6. Phytophotodermatitis is caused by which class of photosensitizing compounds found in plants like lime and celery?

    Answer: Furocoumarins (psoralens)

    Phytophotodermatitis is caused by furocoumarins (psoralens) from plants in the Apiaceae and Rutaceae families, which upon UVA exposure cause phototoxic inflammation.