Heme Mnemonics
The porphyrinogens following PBG conversion into Uroporphryinogen 3 cause photosensitivity because ONLY these react with oxygen on excitation by UV light.
Therefore deficiency of any of the following enzymes -
But between answer choices B & C, C is right because of it's association with Hep C, raised AST ALT as @neonem said.
If you struggle with Biochem and haven't heard of Moof Universitry, I would highly recommend checking it out. The below information I got from this video: https://courses.moofuniversity.com/courses/take/medical-biochemistry-for-usmle-step-1-exam/lessons/4363869-porphyrias-porphyria-cutanea-tarda-pct and it's great.
Porphryia cutanea tarda = AD mutation of uroporphyrinogen decarboxylase, this is the MCC of porphyria, and it presents in 40s-50s.
Main symptom of photosensitivity leading to skin lesions/blisters/bullae due to skin porphyrinogens being oxidized by light to prophryins that damage the skin, and other skin findings of hypertrichosis/hyperpigmentation.
A key feature is possible liver problems due to associated precipitating factors. MCC precipitating factors = excessive EtOH and OCPs because of CYP450 inducers reducing serum heme levels to be utilized in the new CYP450 enzymes, thus stimulating ALA synthase due to decreased heme inhibition. Other precipitating factors include viral hepatitis, especially hepatitis C, and excess iron as in hemochromatosis. These can lead to elevated AST and ALT levels.
Another sign is dark "port-wine" colored urine which pink fluoresces under Wood light. Absent symptoms = abdominal pain and CNS problems because ALA and PBG do not accumulate. Accumulated products = uroporphyrin III, uroporphyrinogen III, uroporphyrin I, and uroporphyrinogen I.
Treatment = sun exposure avoidance, removal of precipitating factors, phlebotomy, chloroquine (which can bind and lead to excretion of accumulations). Prognosis = excellent.
OCPs is associated with Porphyria cutanea tarda as well. in the stem the patient was on OCPs for 15 years.!
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1947755/
https://porphyria.eu/sv/content/hormonal-contraception
submitted by โneonem(630)
This is a case of porphyria cutanea tarda. The way I remember this is that it's the only high-yield porphyria that has skin manifestations due to UV. I remember this by "After U (uroporphyrin), it's UV". Apparently it's also associated with Hepatitis C, which could be the reason why there's increased AST & ALT, or it could be due to toxic buildup of intermediates in heme synthesis.