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Thread: Pku Q

  1. #1
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    Pku Q

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    An old question was: Which amino acid in PKU would you investigate apart from Phenylalanine and Tyrosine? Any ideas?

  2. #2
    Goldspot6 is offline Newbie 510 points
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    You would also investigate the amino acid Tryptophan. In MALIGNANT PKU (not classic PKU), you have a deficiency in dihydrobiopterin reductase which produces a cofactor for phenylalanine hydroxylase... this deficiency leads to increased phenylalanine... also, this same enzyme is used in the conversion of tyrosine to Dopa (via tyrosine hydroxylase)which goes on to produce catecholamines and dopamine... BH4/dihydropbiopterin reductase is also used for the conversion of tryptophan to 5-hydroxytryptophan (via tryptophan hydroxylase) which goes on to produce serotonin, melanin, and niacin..

    so bottom line...

    in classic PKU you monitor Phe and Tyr

    in malignant PKU you monitor Phe, Tyr, and Trp because a cofactor is deficient

    look at a chart of phenylalanine and tyrosine degradation pathways to get a visual..

    hope this helps!

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    Goldspot6 is offline Newbie 510 points
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    oh yea...

    just to be complete..

    in each disorder, you will have increased Phe with toxic neurometabolites and a decrease in Tyr in classic PKU and malignant PKU, but an increase in Trp in malignant PKU.. keep in mind that Trp is not in the degradation pathway of PKU, so you will accumulate it because you can't break it down...

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