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A 10-month-old male is brought to the pediatrician by his mother who is concerned about his lack of interaction. He was previously playful and happy but now hardly ever smiles. On exam, he is found to have poor muscle tone and a cherry-red macula. Deficiency of which enzyme is most likely?

A. Glucocerebrosidase
B. Glucose-6-phosphatase
C. Hexosaminidase A
D. L-iduronidase
E. Tyrosinase
 

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The answer choice is C.
This kid has a lysosomal storage disease called Tay-Sachs (of autosomal recessive inheritance). Clinical findings in these patients are progressive neurodegeneration, hepatosplenomegaly, and cherry-red spot on macula. The enzyme deficient is Hexosaminidase A.

Although is not in the answer choices, you should be able to differentiate this disease from another lysosomal storage disorder called Niemann-Pick disease (autosomal recessive too), in which there's also presence of the cherry-red spot on macula. In this case, the enzyme deficient would be Sphingomyelinase.
 

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I thought tay sachs doesnt have hepatosplenomegaly. I also though that there is a developmental delay when you are very young( The disease is Ar so you will see it early in life and this child almost reaching puberty but again maybe im wrong:(
 

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I dont think that they will waste their time to make lysosomal storage diseases questions hard. There is not something conceptual about it and if there is its minimal. They will try to trick you on other stuff. Thats my opinion. If you will get a lysosomal disease it would be direct with the diagnosis or the maximaml thing they can do is ask you what else is expected to be seen. Pure memorization
 

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I dont think that they will waste their time to make lysosomal storage diseases questions hard. There is not something conceptual about it and if there is its minimal. They will try to trick you on other stuff. Thats my opinion. If you will get a lysosomal disease it would be direct with the diagnosis or the maximaml thing they can do is ask you what else is expected to be seen. Pure memorization
i've seen questions with Tay-Sachs vs NP, only mention of age + bilateral Cherry Red macula.

ie, there was no mention of hepatosplenomegaly or onion skin...
 
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