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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
© Hexosaminidase A
(D) L-iduronidase
(E) Tyrosinase
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Tay-Sacs (Hexoaminidase A)
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© is correct. Tay-Sachs disease is an autosomal
recessive condition with deficiency of hexosaminidase
A. Symptoms begin between 6 to 10 months of age.
There is progressive motor and mental deterioration
with death by 4 years of age. The cherry red spot on
the macula reflects involvement of the retinal ganglion
cells.
Explanation A: No. Deficiency of glucocerebrosidase
results in Gaucher™s disease, the most common
lysosomal storage disease. There are several forms of
the disease, one of which is fatal in infancy with
prominent neurologic signs. Most commonly, patients
suffer the adult form with prominent splenomegaly and
bony complaints.
Explanation B: No. Deficiency of glucose-6-
phosphatase results in von Gierke™s disease with
accumulation of glycogen in the liver. Growth may be
stunted but mentation is preserved.
Explanation D: No. Deficiency of L-iduronidase results
in Hurler™s syndrome, a mucopolysaccharidosis, with
death in early childhood with skeletal abnormalities,
organomegaly, and characteristic facies. There is
corneal clouding.
Explanation E: No. Deficiency of tyrosinase results in
albinism as there no conversion of tyrosine to melanin.
