Maple Syrup Urine Disease

[thinkenergy]

A 5-day-old female newborn who is breast-fed is brought to the emergency department because of a 1-day history of poor feeding, vomiting, and lethargy. Physical examination shows decreased responsiveness, hypotonia, and dehydration. There is a caramel-like odor in the diaper. Serum studies show a decreased glucose concentration, ketones, and metabolic acidosis. Metabolic studies of leukocytes show no conversion of [14C] leucine to 14CO2. An increased plasma concentration of which of the following substances is most likely in this patient?

A ) Alanine
B ) Isovaleric acid
C ) Methylmalonic acid
D ) Phenylalanine
E ) Propionic acid
F ) Valine

Answer given is F). I thought that Leu, Iso, Val can be converted to a-keto acids, but the acids cannot be further metabolized d/t a-keto acid dehydrogenase def, so it is the metabolites that will build up (Isovaleric acid is one of them). What is the right answer?

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[thinkenergy]

Maybe B is wrong b/c isovaleric acid is NOT SAME as alpha keto isovaleric acid?

 

[ijn]

I don't think isovaleric acid is an amino acid metabolite. Wiki says it's a fatty acid.

 

[lemonade90]

A 5-day-old female newborn who is breast-fed is brought to the emergency department because of a 1-day history of poor feeding, vomiting, and lethargy. Physical examination shows decreased responsiveness, hypotonia, and dehydration. There is a caramel-like odor in the diaper. Serum studies show a decreased glucose concentration, ketones, and metabolic acidosis. Metabolic studies of leukocytes show no conversion of [14C] leucine to 14CO2. An increased plasma concentration of which of the following substances is most likely in this patient?

A ) Alanine
B ) Isovaleric acid
C ) Methylmalonic acid
D ) Phenylalanine
E ) Propionic acid
F ) Valine

Answer given is F). I thought that Leu, Iso, Val can be converted to a-keto acids, but the acids cannot be further metabolized d/t a-keto acid dehydrogenase def, so it is the metabolites that will build up (Isovaleric acid is one of them). What is the right answer?

F is right (http://pediatricneuro.com/alfonso/pg75.htm). B is probably wrong because they are asking about what is elevated in PLASMA. The first step prob happens in the muscle so those intermediates stay there.

Not sure if if the ak isovaleric is the same as isovaleric though.

 

[thinkenergy]

So: in maple syrup urine disease, there is ↑Leu, Ile, Val &. ↑α-keto-β-methylvaleric acid, α-ketoisocaproic acid, α-ketoisovaleric acid (from Ile, Leu, Val respectively), really the products built up are the α-ketoacids, and b/c the 3 AA's are their upstream precursors, it follows that they would also get built up?

 

[lemonade90]

So: in maple syrup urine disease, there is ↑Leu, Ile, Val &. ↑α-keto-β-methylvaleric acid, α-ketoisocaproic acid, α-ketoisovaleric acid (from Ile, Leu, Val respectively), really the products built up are the α-ketoacids, and b/c the 3 AA's are their upstream precursors, it follows that they would also get built up?

I guess they can leave...lol. Its been a long day. Either way I would have picked Valine using Occam's razor.