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NBME 23 Answers

nbme23/Block 4/Question#29
A 2-week-old male newborn is brought to the ...
Galactose-1-phosphate uridyltransferase🔍

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Patient is current breast-fed, so we can eliminate fructose (fructose is found in honey and fruits and some formula, but not in breast milk). Patient has reducing substances but no glucose in the urine, so he must some non-glucose sugar. My differential for reducing non-glucose sugars in the urine is disorders fructose metabolism or galactose metabolism. We have eliminated fructose, so that leaves us with galactokinase deficiency or classic galactosemia.

sympathetikey  & Galactokinase deficiency would be much milder. +5  
smc213  Big was soybean formula not giving any issues. Soy-milk can be used as a substitute formula in patients with Classic Galactosemia since it contains sucrose (->fructose and glucose). +1  
oslerweberenu  Why can't this be glucose 6 phosphatase deficiency Confused me +  
almondbreeze  @oslerweberenu G6PD - increased RBC susceptibility to oxidant stress (eg, sulfa drugs, antimalarials, infections, fava beans) -> hemolysis; has nothing to do with presence of reducing sugar +  
makinallkindzofgainz  @almondbreeze; Glucose-6-phosphatase deficiency is Von Gierke disease, they are not referring to G6PD deficiency (an entirely seperate disease) +4  


Fructose is to Aldolase B as Galactose is to Uridyl Transferase. Leads to phosphate depletion.

Fructokinase def and Galactokinase def are kinder.

FA 2018 pg 80

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