COMSAE Phase 1 Form ASA 120
Foundational Biomedical Sciences Exam
Practice Questions & [Verified Answers],
Plus Explained Rationales|2026 Latest
Update| Instant Download PDF
1. A 45-year-old man presents with fatigue, weakness, and jaundice.
Laboratory studies reveal elevated unconjugated bilirubin and
increased lactate dehydrogenase. Peripheral smear shows
spherocytes. Which defect is most likely responsible for this
patient’s condition?
A. Defective spectrin causing RBC membrane instability
B. Defective hemoglobin synthesis
C. Autoantibody-mediated destruction of platelets
D. Impaired DNA synthesis in erythroid precursors
Answer: A. Defective spectrin causing RBC membrane instability
Rationale: Hereditary spherocytosis results from defects in RBC
membrane proteins such as spectrin or ankyrin. These abnormalities
cause spherical RBCs that are trapped and destroyed in the spleen,
producing extravascular hemolysis, jaundice, and splenomegaly.
2. A patient develops confusion, seizures, and severe
hyperammonemia after a high-protein meal. A deficiency in which
enzyme is most likely responsible?
,A. Phenylalanine hydroxylase
B. Ornithine transcarbamylase
C. Homogentisate oxidase
D. Pyruvate dehydrogenase
Answer: B. Ornithine transcarbamylase
Rationale: Ornithine transcarbamylase deficiency is an X-linked urea
cycle disorder causing impaired conversion of ammonia into urea.
Excess ammonia crosses the blood-brain barrier and causes neurologic
symptoms.
3. A child presents with recurrent infections caused by catalase-
positive organisms. Neutrophils fail to generate an oxidative
burst. Which enzyme is defective?
A. Myeloperoxidase
B. NADPH oxidase
C. Superoxide dismutase
D. Glutathione peroxidase
Answer: B. NADPH oxidase
Rationale: Chronic granulomatous disease is caused by NADPH
oxidase deficiency, preventing formation of reactive oxygen species
needed for killing catalase-positive organisms such as Staphylococcus
aureus and Aspergillus.
4. A patient receiving chemotherapy develops peripheral
neuropathy. The medication inhibits microtubule formation.
Which drug is responsible?
,A. Methotrexate
B. Vincristine
C. Cyclophosphamide
D. Bleomycin
Answer: B. Vincristine
Rationale: Vincristine binds tubulin and prevents microtubule
polymerization, inhibiting mitosis. It commonly causes peripheral
neuropathy due to effects on neuronal microtubules.
5. A newborn has hypotonia, developmental delay, and a positive
screening test for elevated phenylalanine. Which enzyme
deficiency causes this disorder?
A. Tyrosinase
B. Phenylalanine hydroxylase
C. Cystathionine beta-synthase
D. Branched-chain alpha-ketoacid dehydrogenase
Answer: B. Phenylalanine hydroxylase
Rationale: Phenylketonuria results from inability to convert
phenylalanine into tyrosine. Accumulated phenylalanine causes
neurotoxicity and developmental impairment.
6. A patient has an infection caused by a gram-positive cocci
arranged in chains. The organism is catalase negative and causes
pharyngitis. Which organism is most likely?
A. Staphylococcus aureus
B. Streptococcus pyogenes
, C. Enterococcus faecalis
D. Streptococcus pneumoniae
Answer: B. Streptococcus pyogenes
Rationale: Streptococcus pyogenes is a group A beta-hemolytic
streptococcus that appears as gram-positive cocci in chains and causes
strep pharyngitis, scarlet fever, and rheumatic fever.
7. A patient with chronic alcohol use develops confusion, ataxia, and
ophthalmoplegia. Which vitamin deficiency is responsible?
A. Vitamin B1
B. Vitamin B6
C. Vitamin B12
D. Folate
Answer: A. Vitamin B1
Rationale: Thiamine deficiency causes Wernicke encephalopathy
characterized by confusion, ataxia, and eye movement abnormalities.
Alcohol impairs thiamine absorption and storage.
8. A patient has prolonged bleeding time but normal PT and PTT.
Which disorder is most likely?
A. Hemophilia A
B. Vitamin K deficiency
C. Platelet dysfunction
D. Disseminated intravascular coagulation
Answer: C. Platelet dysfunction
Foundational Biomedical Sciences Exam
Practice Questions & [Verified Answers],
Plus Explained Rationales|2026 Latest
Update| Instant Download PDF
1. A 45-year-old man presents with fatigue, weakness, and jaundice.
Laboratory studies reveal elevated unconjugated bilirubin and
increased lactate dehydrogenase. Peripheral smear shows
spherocytes. Which defect is most likely responsible for this
patient’s condition?
A. Defective spectrin causing RBC membrane instability
B. Defective hemoglobin synthesis
C. Autoantibody-mediated destruction of platelets
D. Impaired DNA synthesis in erythroid precursors
Answer: A. Defective spectrin causing RBC membrane instability
Rationale: Hereditary spherocytosis results from defects in RBC
membrane proteins such as spectrin or ankyrin. These abnormalities
cause spherical RBCs that are trapped and destroyed in the spleen,
producing extravascular hemolysis, jaundice, and splenomegaly.
2. A patient develops confusion, seizures, and severe
hyperammonemia after a high-protein meal. A deficiency in which
enzyme is most likely responsible?
,A. Phenylalanine hydroxylase
B. Ornithine transcarbamylase
C. Homogentisate oxidase
D. Pyruvate dehydrogenase
Answer: B. Ornithine transcarbamylase
Rationale: Ornithine transcarbamylase deficiency is an X-linked urea
cycle disorder causing impaired conversion of ammonia into urea.
Excess ammonia crosses the blood-brain barrier and causes neurologic
symptoms.
3. A child presents with recurrent infections caused by catalase-
positive organisms. Neutrophils fail to generate an oxidative
burst. Which enzyme is defective?
A. Myeloperoxidase
B. NADPH oxidase
C. Superoxide dismutase
D. Glutathione peroxidase
Answer: B. NADPH oxidase
Rationale: Chronic granulomatous disease is caused by NADPH
oxidase deficiency, preventing formation of reactive oxygen species
needed for killing catalase-positive organisms such as Staphylococcus
aureus and Aspergillus.
4. A patient receiving chemotherapy develops peripheral
neuropathy. The medication inhibits microtubule formation.
Which drug is responsible?
,A. Methotrexate
B. Vincristine
C. Cyclophosphamide
D. Bleomycin
Answer: B. Vincristine
Rationale: Vincristine binds tubulin and prevents microtubule
polymerization, inhibiting mitosis. It commonly causes peripheral
neuropathy due to effects on neuronal microtubules.
5. A newborn has hypotonia, developmental delay, and a positive
screening test for elevated phenylalanine. Which enzyme
deficiency causes this disorder?
A. Tyrosinase
B. Phenylalanine hydroxylase
C. Cystathionine beta-synthase
D. Branched-chain alpha-ketoacid dehydrogenase
Answer: B. Phenylalanine hydroxylase
Rationale: Phenylketonuria results from inability to convert
phenylalanine into tyrosine. Accumulated phenylalanine causes
neurotoxicity and developmental impairment.
6. A patient has an infection caused by a gram-positive cocci
arranged in chains. The organism is catalase negative and causes
pharyngitis. Which organism is most likely?
A. Staphylococcus aureus
B. Streptococcus pyogenes
, C. Enterococcus faecalis
D. Streptococcus pneumoniae
Answer: B. Streptococcus pyogenes
Rationale: Streptococcus pyogenes is a group A beta-hemolytic
streptococcus that appears as gram-positive cocci in chains and causes
strep pharyngitis, scarlet fever, and rheumatic fever.
7. A patient with chronic alcohol use develops confusion, ataxia, and
ophthalmoplegia. Which vitamin deficiency is responsible?
A. Vitamin B1
B. Vitamin B6
C. Vitamin B12
D. Folate
Answer: A. Vitamin B1
Rationale: Thiamine deficiency causes Wernicke encephalopathy
characterized by confusion, ataxia, and eye movement abnormalities.
Alcohol impairs thiamine absorption and storage.
8. A patient has prolonged bleeding time but normal PT and PTT.
Which disorder is most likely?
A. Hemophilia A
B. Vitamin K deficiency
C. Platelet dysfunction
D. Disseminated intravascular coagulation
Answer: C. Platelet dysfunction
