Medical Exam 2024/2025 QUESTION AND ANSWERS (DETAILED)
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(CORRECT ANSWERS)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.
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
E) Tubular necrosis(CORRECT ANSWERS)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
C) Hypoalbuminemia
D) Hyponatremia
E) Increased jugular venous pressure
F) Splenomegaly(CORRECT ANSWERS)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
B) Easy bruising
O C) Eczematous rash
O D) Inability to sweat
O E) Thickened skin
O F) Ulcers(CORRECT ANSWERS)A.
, The hemidesmosome is an intricate complex of proteins whose ultimate function is to
anchor the basal keratinocytes of the epidermis to the dermis at the dermal-
epidermal junction. Any impairment of the hemidesmosome will cause the basal
keratinocytes to
separate from the dermis, causing a blister to form. Because the hemidesmosomes
of neighboring skin are still intact, these will be tense blisters. Anchoring fibrils are
made of type VII collagen and are a component of the hemidesmosome. A mutation
or antibody to
collagen type VII, as seen in epidermolysis bullosa, will cause blistering to occur.
Bullous pemphigoid is another disease which affects the hemidesmosome. In
contrast, pemphigus vulgaris is caused by antibodies to desmosomes, the protein
complex which
maintains cell to cell adhesion in the epidermis. Because the target of pemphigus
vulgaris is more superficial, in the epidermis, those blisters will be fragile and flaccid.
Incorrect Answers: B, C, D, E, and F.
Easy bruising (Choice B) and petechiae may be seen in Vitamin C deficiency, or
scurvy. Vitamin C is necessary to produce collagen, as it is a cofactor in the
hydroxylation of proline and lysine residues, which is a key step in the conversion of
preprocollagen to
procollagen.
Eczematous rashes (Choice C) may be seen in many genetic disorders including
atopic dermatitis, autosomal dominant hyper-IgE syndrome (Job syndrome), and
Wiskott-Aldrich syndrome. While acute eczematous reactions can have small
vesicles due to edema
within the epidermis, blisters are not seen. Itchy, erythematous patches are a classic
finding.
Inability to sweat (Choice D) is seen in a group of inherited disorders called
ectodermal dysplasias. In these disorders, ectoderm-derived structures including the
sweat glands, hair, teeth, and nails are abnormal. The anchoring fibrils are i
5
----------
Exam Section 1: Item 6 of 50
National Board of Medical Examiners
Comprehensive Basic Science Self-Assessment
6. A 62-year-old man is being evaluated for rectal bleeding. An x-ray of the
gastrointestinal tract with contrast material is shown. Which of the following is the
most likely explanation for the feathery appearance
in the portion of the gastrointestinal tract indicated by X when compared with the
portion indicated by Y?
O A) Absence of circular muscle
B) Fewer villi
C) Greater bowel motility
D) Greater mucosal surface area
E) Less circular and longitudinal smooth muscle(CORRECT ANSWERS)D.
The jejunum (X) can be distinguished from the ileum (Y) by several characteristic
features. The inner mucosal folds, or plicae circulares, are more prominent, more
numerous, and taller in the jejunum compared to the ileum. This leads to an
increased mucosal
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(CORRECT ANSWERS)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.
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
E) Tubular necrosis(CORRECT ANSWERS)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
C) Hypoalbuminemia
D) Hyponatremia
E) Increased jugular venous pressure
F) Splenomegaly(CORRECT ANSWERS)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
B) Easy bruising
O C) Eczematous rash
O D) Inability to sweat
O E) Thickened skin
O F) Ulcers(CORRECT ANSWERS)A.
, The hemidesmosome is an intricate complex of proteins whose ultimate function is to
anchor the basal keratinocytes of the epidermis to the dermis at the dermal-
epidermal junction. Any impairment of the hemidesmosome will cause the basal
keratinocytes to
separate from the dermis, causing a blister to form. Because the hemidesmosomes
of neighboring skin are still intact, these will be tense blisters. Anchoring fibrils are
made of type VII collagen and are a component of the hemidesmosome. A mutation
or antibody to
collagen type VII, as seen in epidermolysis bullosa, will cause blistering to occur.
Bullous pemphigoid is another disease which affects the hemidesmosome. In
contrast, pemphigus vulgaris is caused by antibodies to desmosomes, the protein
complex which
maintains cell to cell adhesion in the epidermis. Because the target of pemphigus
vulgaris is more superficial, in the epidermis, those blisters will be fragile and flaccid.
Incorrect Answers: B, C, D, E, and F.
Easy bruising (Choice B) and petechiae may be seen in Vitamin C deficiency, or
scurvy. Vitamin C is necessary to produce collagen, as it is a cofactor in the
hydroxylation of proline and lysine residues, which is a key step in the conversion of
preprocollagen to
procollagen.
Eczematous rashes (Choice C) may be seen in many genetic disorders including
atopic dermatitis, autosomal dominant hyper-IgE syndrome (Job syndrome), and
Wiskott-Aldrich syndrome. While acute eczematous reactions can have small
vesicles due to edema
within the epidermis, blisters are not seen. Itchy, erythematous patches are a classic
finding.
Inability to sweat (Choice D) is seen in a group of inherited disorders called
ectodermal dysplasias. In these disorders, ectoderm-derived structures including the
sweat glands, hair, teeth, and nails are abnormal. The anchoring fibrils are i
5
----------
Exam Section 1: Item 6 of 50
National Board of Medical Examiners
Comprehensive Basic Science Self-Assessment
6. A 62-year-old man is being evaluated for rectal bleeding. An x-ray of the
gastrointestinal tract with contrast material is shown. Which of the following is the
most likely explanation for the feathery appearance
in the portion of the gastrointestinal tract indicated by X when compared with the
portion indicated by Y?
O A) Absence of circular muscle
B) Fewer villi
C) Greater bowel motility
D) Greater mucosal surface area
E) Less circular and longitudinal smooth muscle(CORRECT ANSWERS)D.
The jejunum (X) can be distinguished from the ileum (Y) by several characteristic
features. The inner mucosal folds, or plicae circulares, are more prominent, more
numerous, and taller in the jejunum compared to the ileum. This leads to an
increased mucosal
