NBME 26 EXAM UPDATED QUESTIONS
AND CORRECT ANSWERS.
1
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Exam Section 1: Item 2 of 50
National, Board of Medical Examiners
Comprehensive Basic Science Self-Assessment
2. Free purine and pyrimidine bases are reutilized in normal metabolism. In children with Lesch-
Nyhan syndrome who have intellectual disability, poor muscle coordination, and self-mutilation
tendencies, there is a defect in the salvage of which of the following
pairs of bases?
A) Adenine and thymine
B) Guanine and hypoxanthine
C) Guanine and uric acid
D) Uracil and cytosine
E) Xanthine and hypoxanthine - ANS B.
Lesch-Nyhan syndrome presents with intellectual disability, aggressive behavior, self-
mutilation, gout, and dystonia. The disorder is due to inactivating mutations of hypoxanthine-
guanine phosphoribosyltransferase (HGPRT), a key enzyme in the purine salvage
pathway, and is inherited in an X-linked recessive fashion. HGPRT catalyzes the conversion of
guanine to guanosine monophosphate and hypoxanthine to inosine monophosphate. Patients
with deficient activity of HGPRT are unable to salvage guanine and
hypoxanthine and develop resultant increased levels of xanthine and uric acid. Hyperuricemia
in Lesch-Nyhan syndrome is treated with xanthine oxidase inhibitors, such as allopurinol or
febuxostat, in order to reduce the synthesis of uric acid.
1 @COPYRIGHT 2025/2026 ALLRIGHTS RESERVED
,Incorrect Answers: A, C, D and E.
Adenine and thymine (Choice A) are purine and pyrimidine bases, respectively. Purine and
pyrimidine salvage are handled through two distinct pathways that are not commonly involved
in a single disease process.
Guanine and uric acid (Choice C) accumulation may occur as part of Lesch-Nyhan syndrome,
however, the accumulation of uric acid is also secondary to accumulation of hypoxanthine.
Choice B more accurately describes defective salvage of guanine and
hypoxanthine as the fundamental effect of HGPRT dysfunction. The accumulation of uric acid is
secondary.
Uracil and cytosine (Choice D) are pyrimidine nucleotides. Pyrimidine salvage is not affected by
mutations of HGPRT.
Defects of xanthine and hypoxanthine (Choice E) metabolism may result from defects in HGPRT.
However, HGPRT dysfunction results in impaired hypoxanthine salvage with resultant excessive
production of xanthine, rather than impaired xanthine salvage.
Educational Objective: Lesch-Nyhan syndrome presents with intellectual disability, aggressive
behavior, self-mutilation, gout, and dyst
2
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Exam Section 1: Item 3 of 50
National Board of Medical Examiners
Comprehensive Basic Science Self-Assessment
3. A 42-year-old man is struck by a motor vehicle. His only injury is a closed fracture of the
proximal tibia. Initial neurovascular examination shows no deficits. Twenty-four hours later, he
has increased leg pain and paresthesias in the dorsal space between his
first and second toes. The patient begins to pass dark red urine and becomes oliguric. Urinalysis
is positive for blood but no erythrocytes are seen on microscopic examination. Which of the
following acute disorders is the most likely cause of the renal
failure?
A) Glomerulonephritis
B) Hemolytic-uremic syndrome
C) Interstitial nephritis
D) Nephrotic syndrome
2 @COPYRIGHT 2025/2026 ALLRIGHTS RESERVED
,E) Tubular necrosis - ANS E.
Tibial fractures present a high risk for compartment syndrome. The fracture results in blood
vessel injury and muscle injury, inflammation, and edema. Because the fascia containing the
anterior compartment of the leg does not stretch, bleeding and swelling can
cause increased pressure in the compartment. This increased pressure in turn inhibits venous
drainage, further increasing pressure in the compartment. Eventually the nerve supply and
associated arteries are compromised, leading to the classic signs and
symptoms of compartment syndrome. Signs and symptoms of compartment syndrome include
pain out of proportion to examination findings, pain with passive movement of the muscles,
paresthesia, pallor, pulselessness, and paralysis. Compromised blood supply
deprives muscle and tissue of oxygen and glucose, leading to tissue ischemia and necrosis.
Muscle necrosis leads to rhabdomyolysis, myoglobinuria, and acute renal failure. Evaluation of
rhabdomyolysis reveals red or brown urine and urinalysis is typically positive
for blood due to the presence of myoglobinuria without microscopic evidence of red blood
cells. A complication of rhabdomyolysis is acute kidney injury from acute tubular necrosis
secondary to the release of nephrotoxic myoglobin and nonprotein heme pigments.
Acute tubular necrosis typically occurs following an ischemic or nephrotoxic insult to the
kidneys, which results in loss of the tubular epithelium. Granular, muddy brown casts are
common on urinalysis. Compartment syndrome is treated by immediate fasciotomy to
decrease compartment pressure and support tissue perfusion.
Incorrect Answers: A, B, C, and D.
Glomerulonephritis (Choice A) refers to a variety of glomerular diseases, including nephritic and
nephrotic syndromes. Nephritic syndromes typically present with acute renal failure associated
with h
3
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Exam Section 1: Item 5 of 50
National, Board of Medical Examiners
Comprehensive Basic Science Self-Assessment
5. A 65-year-old woman has ascites. Which of the following additional findings indicates a
diagnosis of constrictive pericarditis rather than cirrhosis?
O A) Edema of the lower extremities
B) Esophageal varices
3 @COPYRIGHT 2025/2026 ALLRIGHTS RESERVED
, C) Hypoalbuminemia
D) Hyponatremia
E) Increased jugular venous pressure
F) Splenomegaly - ANS E.
Increased jugular venous pressure (JVP) is an expected finding in constrictive pericarditis (CP)
and would not be found in patients with volume overload secondary to cirrhosis. CP describes a
pathologic state whereby the pericardium, which encases the entirety of
the heart and the origins of the great vessels, loses its elasticity. This can occur in patients with
viral infections, connective tissue disease, tuberculosis, or as a result of cardiac surgery or
radiation. During the normal cardiac cycle, increased venous return to the
right atrium (RA) and right ventricle (RV) during inspiration leads to transient expansion of the
RV with slight bowing of the interventricular septum into the left ventricle (LV). This increased
RV preload does not impair LV filling as the pericardial sac expands to
accommodate the increased RV volume. In constrictive pericarditis, the pericardial sac loses its
elasticity. When venous return to the right heart increases, the pericardial sac is unable to
expand, which exacerbates movement of the interventricular septum into the
LV. This impairs diastolic filling of the LV and reduces cardiac output. LV diastolic filling is
further reduced by a reduction in preload from the pulmonary veins. The constricted
pericardium does not respond to normal changes in intrathoracic pressure during
inspiration, but the pulmonary venous system, which lies outside of the pericardium,
experiences a normal drop in pressure during inspiration. This difference creates an abnormal
pressure gradient that reduces LV preload and leads to reduced cardiac output. The
RV and LV develop interventricular dependence whereby increased pressure in each ventricle
begins to affect the other ventricle. CP ultimately results in equalization of pressures in all four
chambers, with clinical evidence of right heart failure exhib
4
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Exam Section 1: Item 4 of 50
National Board of Medical Examiners
Comprehensive Basic Science Self-Assessment
4. A male newborn is found to have a defect in anchoring fibrils. Which of the following skin
findings is most likely in this patient?
A) Blisters
4 @COPYRIGHT 2025/2026 ALLRIGHTS RESERVED
AND CORRECT ANSWERS.
1
----------
Exam Section 1: Item 2 of 50
National, Board of Medical Examiners
Comprehensive Basic Science Self-Assessment
2. Free purine and pyrimidine bases are reutilized in normal metabolism. In children with Lesch-
Nyhan syndrome who have intellectual disability, poor muscle coordination, and self-mutilation
tendencies, there is a defect in the salvage of which of the following
pairs of bases?
A) Adenine and thymine
B) Guanine and hypoxanthine
C) Guanine and uric acid
D) Uracil and cytosine
E) Xanthine and hypoxanthine - ANS B.
Lesch-Nyhan syndrome presents with intellectual disability, aggressive behavior, self-
mutilation, gout, and dystonia. The disorder is due to inactivating mutations of hypoxanthine-
guanine phosphoribosyltransferase (HGPRT), a key enzyme in the purine salvage
pathway, and is inherited in an X-linked recessive fashion. HGPRT catalyzes the conversion of
guanine to guanosine monophosphate and hypoxanthine to inosine monophosphate. Patients
with deficient activity of HGPRT are unable to salvage guanine and
hypoxanthine and develop resultant increased levels of xanthine and uric acid. Hyperuricemia
in Lesch-Nyhan syndrome is treated with xanthine oxidase inhibitors, such as allopurinol or
febuxostat, in order to reduce the synthesis of uric acid.
1 @COPYRIGHT 2025/2026 ALLRIGHTS RESERVED
,Incorrect Answers: A, C, D and E.
Adenine and thymine (Choice A) are purine and pyrimidine bases, respectively. Purine and
pyrimidine salvage are handled through two distinct pathways that are not commonly involved
in a single disease process.
Guanine and uric acid (Choice C) accumulation may occur as part of Lesch-Nyhan syndrome,
however, the accumulation of uric acid is also secondary to accumulation of hypoxanthine.
Choice B more accurately describes defective salvage of guanine and
hypoxanthine as the fundamental effect of HGPRT dysfunction. The accumulation of uric acid is
secondary.
Uracil and cytosine (Choice D) are pyrimidine nucleotides. Pyrimidine salvage is not affected by
mutations of HGPRT.
Defects of xanthine and hypoxanthine (Choice E) metabolism may result from defects in HGPRT.
However, HGPRT dysfunction results in impaired hypoxanthine salvage with resultant excessive
production of xanthine, rather than impaired xanthine salvage.
Educational Objective: Lesch-Nyhan syndrome presents with intellectual disability, aggressive
behavior, self-mutilation, gout, and dyst
2
----------
Exam Section 1: Item 3 of 50
National Board of Medical Examiners
Comprehensive Basic Science Self-Assessment
3. A 42-year-old man is struck by a motor vehicle. His only injury is a closed fracture of the
proximal tibia. Initial neurovascular examination shows no deficits. Twenty-four hours later, he
has increased leg pain and paresthesias in the dorsal space between his
first and second toes. The patient begins to pass dark red urine and becomes oliguric. Urinalysis
is positive for blood but no erythrocytes are seen on microscopic examination. Which of the
following acute disorders is the most likely cause of the renal
failure?
A) Glomerulonephritis
B) Hemolytic-uremic syndrome
C) Interstitial nephritis
D) Nephrotic syndrome
2 @COPYRIGHT 2025/2026 ALLRIGHTS RESERVED
,E) Tubular necrosis - ANS E.
Tibial fractures present a high risk for compartment syndrome. The fracture results in blood
vessel injury and muscle injury, inflammation, and edema. Because the fascia containing the
anterior compartment of the leg does not stretch, bleeding and swelling can
cause increased pressure in the compartment. This increased pressure in turn inhibits venous
drainage, further increasing pressure in the compartment. Eventually the nerve supply and
associated arteries are compromised, leading to the classic signs and
symptoms of compartment syndrome. Signs and symptoms of compartment syndrome include
pain out of proportion to examination findings, pain with passive movement of the muscles,
paresthesia, pallor, pulselessness, and paralysis. Compromised blood supply
deprives muscle and tissue of oxygen and glucose, leading to tissue ischemia and necrosis.
Muscle necrosis leads to rhabdomyolysis, myoglobinuria, and acute renal failure. Evaluation of
rhabdomyolysis reveals red or brown urine and urinalysis is typically positive
for blood due to the presence of myoglobinuria without microscopic evidence of red blood
cells. A complication of rhabdomyolysis is acute kidney injury from acute tubular necrosis
secondary to the release of nephrotoxic myoglobin and nonprotein heme pigments.
Acute tubular necrosis typically occurs following an ischemic or nephrotoxic insult to the
kidneys, which results in loss of the tubular epithelium. Granular, muddy brown casts are
common on urinalysis. Compartment syndrome is treated by immediate fasciotomy to
decrease compartment pressure and support tissue perfusion.
Incorrect Answers: A, B, C, and D.
Glomerulonephritis (Choice A) refers to a variety of glomerular diseases, including nephritic and
nephrotic syndromes. Nephritic syndromes typically present with acute renal failure associated
with h
3
----------
Exam Section 1: Item 5 of 50
National, Board of Medical Examiners
Comprehensive Basic Science Self-Assessment
5. A 65-year-old woman has ascites. Which of the following additional findings indicates a
diagnosis of constrictive pericarditis rather than cirrhosis?
O A) Edema of the lower extremities
B) Esophageal varices
3 @COPYRIGHT 2025/2026 ALLRIGHTS RESERVED
, C) Hypoalbuminemia
D) Hyponatremia
E) Increased jugular venous pressure
F) Splenomegaly - ANS E.
Increased jugular venous pressure (JVP) is an expected finding in constrictive pericarditis (CP)
and would not be found in patients with volume overload secondary to cirrhosis. CP describes a
pathologic state whereby the pericardium, which encases the entirety of
the heart and the origins of the great vessels, loses its elasticity. This can occur in patients with
viral infections, connective tissue disease, tuberculosis, or as a result of cardiac surgery or
radiation. During the normal cardiac cycle, increased venous return to the
right atrium (RA) and right ventricle (RV) during inspiration leads to transient expansion of the
RV with slight bowing of the interventricular septum into the left ventricle (LV). This increased
RV preload does not impair LV filling as the pericardial sac expands to
accommodate the increased RV volume. In constrictive pericarditis, the pericardial sac loses its
elasticity. When venous return to the right heart increases, the pericardial sac is unable to
expand, which exacerbates movement of the interventricular septum into the
LV. This impairs diastolic filling of the LV and reduces cardiac output. LV diastolic filling is
further reduced by a reduction in preload from the pulmonary veins. The constricted
pericardium does not respond to normal changes in intrathoracic pressure during
inspiration, but the pulmonary venous system, which lies outside of the pericardium,
experiences a normal drop in pressure during inspiration. This difference creates an abnormal
pressure gradient that reduces LV preload and leads to reduced cardiac output. The
RV and LV develop interventricular dependence whereby increased pressure in each ventricle
begins to affect the other ventricle. CP ultimately results in equalization of pressures in all four
chambers, with clinical evidence of right heart failure exhib
4
----------
Exam Section 1: Item 4 of 50
National Board of Medical Examiners
Comprehensive Basic Science Self-Assessment
4. A male newborn is found to have a defect in anchoring fibrils. Which of the following skin
findings is most likely in this patient?
A) Blisters
4 @COPYRIGHT 2025/2026 ALLRIGHTS RESERVED
