MedLect USMLE Answers & Rationales |
Comprehensive Q& A | Grade A | 100% Correct -The
Ultimate Guide for Yr. (2026/2027)
Generated: 10/9/2025
Question 1:
A newborn present with severe hypoglycemia, massive hepatomegaly,
and failure to thrive. Lab results show hyperuricemia and hyperlipidemia.
Which enzyme deficiency is most likely?
A) Glucose-6-phosphatase
B) Alpha-1,4-glucosidase
C) Amylo-1,6-glucosidase
D) Branching enzyme
E) Phosphorylase
Rationale:
The clinical picture points towards Von Gierke disease (Type I GSD), which results
from a deficiency in glucose-6-phosphatase. This leads to impaired glucose release
from the liver, causing hypoglycemia and the accumulation of glycogen and its
byproducts.
Learning Outcomes:
Glycogen Storage Disease Type I, Von Gierke disease, glucose-6-phosphatase
deficiency
Question 2:
A 2-year-old child experiences progressive muscle weakness and
cardiorespiratory failure, leading to death. An autopsy reveals excessive
glycogen accumulation in all organs. Which enzyme deficiency is the
most probable cause?
A) Glucose-6-phosphatase
B) Alpha-1,4-glucosidase
C) Amylo-1,6-glucosidase
D) Branching enzyme
, E) Phosphorylase
Rationale:
The clinical scenario is indicative of Pompe disease (Type II GSD), caused by a
deficiency in alpha-1,4-glucosidase (acid maltase). This enzyme is responsible for
glycogen degradation in lysosomes, and its deficiency leads to glycogen
accumulation in various organs, especially the heart and muscles.
Learning Outcomes:
Glycogen Storage Disease Type II, Pompe disease, alpha-1,4-glucosidase
deficiency
Question 3:
A patient presents with muscle cramps and limited ability to perform
strenuous exercise. Further testing reveals moderately increased
glycogen levels in muscle tissue with normal glycogen structure. Which
enzyme is most likely deficient?
A) Glucose-6-phosphatase
B) Alpha-1,4-glucosidase
C) Amylo-1,6-glucosidase
D) Branching enzyme
E) Phosphorylase
Rationale:
The symptoms align with McArdle disease (Type V GSD), which is caused by a
deficiency in muscle phosphorylase. This enzyme is essential for glycogen
breakdown in muscle tissue, and its deficiency impairs energy production during
exercise, leading to muscle cramps.
Learning Outcomes:
Glycogen Storage Disease Type V, McArdle disease, muscle phosphorylase
deficiency
Question 4:
Comprehensive Q& A | Grade A | 100% Correct -The
Ultimate Guide for Yr. (2026/2027)
Generated: 10/9/2025
Question 1:
A newborn present with severe hypoglycemia, massive hepatomegaly,
and failure to thrive. Lab results show hyperuricemia and hyperlipidemia.
Which enzyme deficiency is most likely?
A) Glucose-6-phosphatase
B) Alpha-1,4-glucosidase
C) Amylo-1,6-glucosidase
D) Branching enzyme
E) Phosphorylase
Rationale:
The clinical picture points towards Von Gierke disease (Type I GSD), which results
from a deficiency in glucose-6-phosphatase. This leads to impaired glucose release
from the liver, causing hypoglycemia and the accumulation of glycogen and its
byproducts.
Learning Outcomes:
Glycogen Storage Disease Type I, Von Gierke disease, glucose-6-phosphatase
deficiency
Question 2:
A 2-year-old child experiences progressive muscle weakness and
cardiorespiratory failure, leading to death. An autopsy reveals excessive
glycogen accumulation in all organs. Which enzyme deficiency is the
most probable cause?
A) Glucose-6-phosphatase
B) Alpha-1,4-glucosidase
C) Amylo-1,6-glucosidase
D) Branching enzyme
, E) Phosphorylase
Rationale:
The clinical scenario is indicative of Pompe disease (Type II GSD), caused by a
deficiency in alpha-1,4-glucosidase (acid maltase). This enzyme is responsible for
glycogen degradation in lysosomes, and its deficiency leads to glycogen
accumulation in various organs, especially the heart and muscles.
Learning Outcomes:
Glycogen Storage Disease Type II, Pompe disease, alpha-1,4-glucosidase
deficiency
Question 3:
A patient presents with muscle cramps and limited ability to perform
strenuous exercise. Further testing reveals moderately increased
glycogen levels in muscle tissue with normal glycogen structure. Which
enzyme is most likely deficient?
A) Glucose-6-phosphatase
B) Alpha-1,4-glucosidase
C) Amylo-1,6-glucosidase
D) Branching enzyme
E) Phosphorylase
Rationale:
The symptoms align with McArdle disease (Type V GSD), which is caused by a
deficiency in muscle phosphorylase. This enzyme is essential for glycogen
breakdown in muscle tissue, and its deficiency impairs energy production during
exercise, leading to muscle cramps.
Learning Outcomes:
Glycogen Storage Disease Type V, McArdle disease, muscle phosphorylase
deficiency
Question 4:
