NBME 24 Tyrosine (NBME Answers)

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submitted by ∗zelderonmorningstar(96)

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Can someone explain why the answer couldn’t be phenylalanine?

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donutsnduodenums The kid has albinism, which is due to decreased tyrosinase activity. If he has a problem metabolizing Phenylalanine, he would be presenting with the PKU sx like intellectual disability, musty body odor, etc., in addition to his fair complexion. +22

zelderonmorningstar I see, so if it was PKU he wouldn’t just be presenting for a routine examination. It would be one of those “oh crap what’s wrong with my baby” ones. +16

wowo FA2019 p83 +

nbme4unme Just a note that UWorld says phenylketonuria patients ALSO have albinism, it's just that the neuro sx and musty order are giveaways. +4

pathogen7 Technically, albinism is a problem processing DOPA, and not tyrosine, no? I always associated "tyrosine processing defect" with ochronosis, which is why I didn't choose tyrosine. Guess I'm wrong. +5

cmun777 @pathogen7 you're not wrong it is specifically DOPA but would any of the other answer choices make any sense over tyrosine? +5

qiss @pathogen7 also yes- you can't make DOPA because of a defective tyrosinase enzyme. This enzyme also metabolizes tyrosine into DOPA before it metabolizes DOPA https://www.google.com/search?q=tyrosinase&sxsrf=ALeKk021WaFQzRNr99BZVujxqRii-GzV6g:1585781210231&source=lnms&tbm=isch&sa=X&ved=2ahUKEwjzt-itp8joAhVDMqwKHUGYC3wQ_AUoAXoECBgQAw&biw=1280&bih=720#imgrc=MyxHLTV0gV7BKM +

qiss link fixed hopefully +1

PKU commonly results from deficiencies in the enzyme phenylalanine hydroxylase, which converts phenylalanine to tyrosine.
Tyrosine, in turn, is required for synthesis of the catecholamines dopamine, norepinephrine, and epinephrine.
Supplementation with tyrosine effectively bypasses the defective enzyme and allows for the normal synthesis of catecholamines

+/- namesthegame22(13)