Homocystinuria and essential/restricted Amino Acids

[theshellyb]

So, homocystinuria has 3 underlying causes. 2 of them relate to defective cystathione synthase, so you have reduced cystathione/cysteine and too much methionine (due to homocysteine shunting to methionine production). For that you would decrease methionine in the diet and increase cysteine. Fine, makes sense.

What about the cause of homocystinuria with a homocysteine methyltransferase deficiency? Would you then have to supplement methionine and decreasse cysteine in the diet? I mean it would make sense, but in FA it only lists the treatment as "supplement B12" and I've never seen the opposite combination of amino acids to restrict/supplement listed in any Q banks.

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[theshellyb]

Anyone? This has been bugging me for a while...

 

[wanderer]

I would assume that in cases where supplementing b12 doesn't work you would have to supplement/restrict the opposite set of amino acids. That's assuming that the enzyme can't be supplemented. It's pretty low yield for the boards, but you can probably find the answer on uptodate.

 

[theshellyb]

I would assume that in cases where supplementing b12 doesn't work you would have to supplement/restrict the opposite set of amino acids. That's assuming that the enzyme can't be supplemented. It's pretty low yield for the boards, but you can probably find the answer on uptodate.

So for boards would you just recommend ignoring the fact that homocystinuria could be caused by the homocysteine methyltransferase/methionine synthase deficiency and go with the answer always being the cystathione synthase deficiency instead? I think that will be my plan. (Cysteine + B6 + B12 as treatment)

As for UpToDate, I learned from M1 summer working with medical geneticists that UpToDate is generally awful for genetic issues, especially inborn errors of metabolism. GeneReviews tends to be much better.

http://www.ncbi.nlm.nih.gov/books/NBK1328/

Found this: "Methionine supplementation. Hypomethioninemia associated with MUT/MTR and MTR-only disorders have been treated with methionine supplementation. The efficacy of this therapy is uncertain."

They mentioned B12 supplementation, but data on supplementing the opposite amino acids I guess is lacking.

 

[wanderer]

So If treatment is experimental it's unlikely they'd ask about it. Just know that in theory at least reducing cysteine and supplementing methionine might work.