Repeated USMLE Questions Step 1 | Review

Q- A 6-month-old infant presents with developmental delay, hypotonia, and a cherry-red spot on retinal examination. There is no hepatosplenomegaly. Which enzyme deficiency is most likely responsible for this condition?

A- Arylsulfatase A

B- β-Hexosaminidase A

C- Glucocerebrosidase

D- Sphingomyelinase

B- β-Hexosaminidase A- Tay-Sachs disease results from deficiency of β-hexosaminidase A, causing the accumulation of GM2 ganglioside. It presents with neurodegeneration and cherry-red macula without hepatosplenomegaly.

Q- A researcher is studying oxygen delivery in tissues. Which factor shifts the oxyhemoglobin dissociation curve to the right?

A- Decreased 2,3-BPG

B- Decreased temperature

C- Increased PCO₂

D- Increased pH

C- Increased PCO₂- Increased PCO₂, decreased pH, increased temperature, and increased 2,3-BPG shift the curve to the right, promoting oxygen unloading to tissues (Bohr effect).

Q- A patient with chronic kidney disease develops hypocalcemia. Which hormone normally increases renal calcium reabsorption in the distal tubule?

A- Aldosterone

B- Calcitonin

C- Parathyroid hormone

D- Vasopressin

C- Parathyroid hormone- PTH increases calcium reabsorption in the distal convoluted tubule, decreases phosphate reabsorption in the proximal tubule, and stimulates vitamin D activation.

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