COMSAE PHASE 1 FORM 113 EXAM / COMSAE FORM 113
ACTUAL PHASE 1 COMPLETE ACCURATE QUESTIONS WITH
WELL ELABORATED ANSWERS AND RATIONALES (100%
CORRECT VERIFIED SOLUTIONS) NEWEST UPDATED VERSION
Question 1: A 24-year-old medical student presents with fatigue, pallor, and shortness
of breath on exertion. Laboratory studies reveal a hemoglobin of 9.2 g/dL, mean
corpuscular volume of 72 fL, and serum ferritin of 8 ng/mL. Which of the following is
the most likely underlying mechanism of this patient’s anemia?
A. Decreased erythropoietin production B. Impaired DNA synthesis in erythroid precursors
C. Reduced iron availability for hemoglobin synthesis D. Autoimmune destruction of mature
erythrocytes
CORRECT ANSWER: C. Reduced iron availability for hemoglobin synthesis
Rationale: The laboratory findings of microcytic anemia with low ferritin are diagnostic of
iron-deficiency anemia. Iron is an essential component of heme; its deficiency directly
impairs hemoglobin synthesis, leading to small, pale red blood cells.
Question 2: A 55-year-old man with a long history of alcohol use disorder is brought to
the emergency department because of confusion and ataxia. Physical examination
shows ophthalmoplegia and nystagmus. Administration of which of the following is
the most appropriate initial treatment?
A. High-dose folate B. Intravenous thiamine C. Oral vitamin B12 D. Glucose infusion before
vitamin supplementation
CORRECT ANSWER: B. Intravenous thiamine
Rationale: The clinical triad of encephalopathy, oculomotor dysfunction, and gait ataxia is
characteristic of Wernicke encephalopathy, caused by thiamine (vitamin B1) deficiency.
Immediate parenteral thiamine is required to prevent progression to irreversible Korsakoff
psychosis.
Question 3: During embryonic development, the midgut herniates into the umbilical
cord and later returns to the abdominal cavity while rotating. Failure of the midgut to
return to the abdomen results in which of the following congenital anomalies?
A. Gastroschisis B. Omphalocele C. Meckel diverticulum D. Hirschsprung disease
CORRECT ANSWER: B. Omphalocele
Rationale: Omphalocele results from persistent herniation of abdominal contents into the
umbilical cord due to failure of the midgut to return to the abdominal cavity during weeks
,10–11 of development. The herniated viscera are covered by a peritoneum-amnion
membrane.
Question 4: A 28-year-old woman presents with a 3-month history of intermittent
double vision and fatigable muscle weakness that worsens throughout the day.
Administration of edrophonium produces transient improvement in her symptoms.
Antibodies against which of the following structures are most likely responsible for
her condition?
A. Presynaptic voltage-gated calcium channels B. Postsynaptic nicotinic acetylcholine
receptors C. Muscle-specific kinase (MuSK) only D. Voltage-gated sodium channels
CORRECT ANSWER: B. Postsynaptic nicotinic acetylcholine receptors
Rationale: Myasthenia gravis is an autoimmune disorder caused by antibodies directed
against postsynaptic nicotinic acetylcholine receptors at the neuromuscular junction,
leading to receptor degradation and blockade. The edrophonium (Tensilon) test produces
transient improvement by inhibiting acetylcholinesterase.
Question 5: A 45-year-old man is diagnosed with a pheochromocytoma. Which of the
following enzymes catalyzes the rate-limiting step in the synthesis of the
catecholamines produced by this tumor?
A. Dopamine β-hydroxylase B. Phenylethanolamine N-methyltransferase C. Tyrosine
hydroxylase D. Dopa decarboxylase
CORRECT ANSWER: C. Tyrosine hydroxylase
Rationale: Tyrosine hydroxylase converts tyrosine to L-DOPA and is the rate-limiting enzyme
in catecholamine biosynthesis. Pheochromocytomas produce excess catecholamines
through this pathway.
Question 6: A 3-year-old boy is brought to the physician because of recurrent bacterial
infections and the absence of tonsils and palpable lymph nodes. Flow cytometry of
peripheral blood shows markedly decreased B cells but normal T-cell numbers.
Which of the following is the most likely diagnosis?
A. DiGeorge syndrome B. X-linked agammaglobulinemia C. Severe combined
immunodeficiency D. Chronic granulomatous disease
CORRECT ANSWER: B. X-linked agammaglobulinemia
Rationale: X-linked agammaglobulinemia (Bruton) results from a defect in Bruton tyrosine
kinase, preventing B-cell maturation. Patients have absent or very low B cells, absent
lymphoid tissue, and recurrent bacterial infections after maternal antibodies wane, while T-
cell numbers remain normal.
,Question 7: A 60-year-old woman with a history of rheumatoid arthritis has been taking
methotrexate for 8 years. She now has macrocytic anemia and elevated serum
homocysteine. Which of the following enzymatic reactions is most directly impaired
by her medication?
A. Conversion of methylmalonyl-CoA to succinyl-CoA B. Transfer of one-carbon units by
tetrahydrofolate C. Hydroxylation of proline in collagen D. Carboxylation of clotting factors
CORRECT ANSWER: B. Transfer of one-carbon units by tetrahydrofolate
Rationale: Methotrexate inhibits dihydrofolate reductase, depleting tetrahydrofolate.
Tetrahydrofolate is required as a carrier of one-carbon units for nucleotide synthesis and
regeneration of methionine from homocysteine, explaining the macrocytic anemia and
elevated homocysteine.
Question 8: A newborn is noted to have a left-sided flank mass. Imaging reveals fusion
of the inferior poles of the kidneys. Which of the following embryonic structures failed
to undergo normal development or migration?
A. Ureteric bud B. Metanephric mesenchyme C. Ascent and rotation of the kidneys D.
Mesonephric duct
CORRECT ANSWER: C. Ascent and rotation of the kidneys
Rationale: Horseshoe kidney results when the inferior poles of the kidneys fuse in the pelvis.
During ascent, the fused kidney is trapped under the inferior mesenteric artery, preventing
normal ascent and rotation.
Question 9: A 35-year-old man presents with a chronic cough and recurrent
pneumonia. Chest CT shows dilated bronchi with tram-track opacities. He also has a
long history of sinusitis and infertility. Which of the following is the most likely
underlying defect?
A. Defective chloride transport B. Immotile cilia due to dynein arm dysfunction C. Alpha-1
antitrypsin deficiency D. Hypersensitivity to Aspergillus
CORRECT ANSWER: B. Immotile cilia due to dynein arm dysfunction
Rationale: Kartagener syndrome (a form of primary ciliary dyskinesia) is caused by dynein
arm defects leading to immotile cilia. Clinical features include chronic sinusitis,
bronchiectasis, situs inversus (in some cases), and infertility due to immotile sperm.
Question 10: A 50-year-old man with longstanding type 2 diabetes mellitus has a
serum creatinine of 2.8 mg/dL and 4 g of proteinuria per day. Renal biopsy is most
likely to show which of the following findings?
, A. Linear IgG deposition along the glomerular basement membrane B. Nodular
glomerulosclerosis with Kimmelstiel-Wilson nodules C. Subepithelial humps on electron
microscopy D. Wire-loop lesions
CORRECT ANSWER: B. Nodular glomerulosclerosis with Kimmelstiel-Wilson nodules
Rationale: Diabetic nephropathy is characterized by mesangial expansion, basement-
membrane thickening, and pathognomonic Kimmelstiel-Wilson nodules (nodular
glomerulosclerosis). Heavy proteinuria is typical in advanced disease.
Question 11: A 22-year-old woman is started on isotretinoin for severe acne. She must
be counseled about the teratogenic risk of this medication because it disrupts which of
the following developmental processes?
A. Neural tube closure via folate antagonism B. Patterning of the limbs and pharyngeal
arches via retinoic acid excess C. Cardiac septation via impaired neural crest migration only
D. Renal ascent
CORRECT ANSWER: B. Patterning of the limbs and pharyngeal arches via retinoic acid
excess
Rationale: Isotretinoin is a potent teratogen that causes retinoic acid embryopathy,
characterized by craniofacial, cardiac, thymic, and central nervous system anomalies due to
disruption of Hox gene-mediated patterning and neural-crest migration.
Question 12: A 40-year-old woman has a serum calcium of 11.8 mg/dL, elevated
parathyroid hormone, and a neck mass. Which of the following is the most likely
mechanism of hypercalcemia?
A. Increased osteoblast activity B. Increased osteoclast activity mediated by RANKL C.
Decreased intestinal calcium absorption D. Increased renal calcium excretion
CORRECT ANSWER: B. Increased osteoclast activity mediated by RANKL
Rationale: Primary hyperparathyroidism increases PTH, which stimulates osteoblasts to
express RANKL. RANKL activates osteoclasts, increasing bone resorption and releasing
calcium into the serum.
Question 13: A 65-year-old man with a 40-pack-year smoking history presents with
proximal muscle weakness and fatigability that improves with repeated use.
Antibodies to which of the following are most likely present?
A. Postsynaptic acetylcholine receptors B. Presynaptic voltage-gated calcium channels C.
Muscle-specific kinase D. Titin
CORRECT ANSWER: B. Presynaptic voltage-gated calcium channels
ACTUAL PHASE 1 COMPLETE ACCURATE QUESTIONS WITH
WELL ELABORATED ANSWERS AND RATIONALES (100%
CORRECT VERIFIED SOLUTIONS) NEWEST UPDATED VERSION
Question 1: A 24-year-old medical student presents with fatigue, pallor, and shortness
of breath on exertion. Laboratory studies reveal a hemoglobin of 9.2 g/dL, mean
corpuscular volume of 72 fL, and serum ferritin of 8 ng/mL. Which of the following is
the most likely underlying mechanism of this patient’s anemia?
A. Decreased erythropoietin production B. Impaired DNA synthesis in erythroid precursors
C. Reduced iron availability for hemoglobin synthesis D. Autoimmune destruction of mature
erythrocytes
CORRECT ANSWER: C. Reduced iron availability for hemoglobin synthesis
Rationale: The laboratory findings of microcytic anemia with low ferritin are diagnostic of
iron-deficiency anemia. Iron is an essential component of heme; its deficiency directly
impairs hemoglobin synthesis, leading to small, pale red blood cells.
Question 2: A 55-year-old man with a long history of alcohol use disorder is brought to
the emergency department because of confusion and ataxia. Physical examination
shows ophthalmoplegia and nystagmus. Administration of which of the following is
the most appropriate initial treatment?
A. High-dose folate B. Intravenous thiamine C. Oral vitamin B12 D. Glucose infusion before
vitamin supplementation
CORRECT ANSWER: B. Intravenous thiamine
Rationale: The clinical triad of encephalopathy, oculomotor dysfunction, and gait ataxia is
characteristic of Wernicke encephalopathy, caused by thiamine (vitamin B1) deficiency.
Immediate parenteral thiamine is required to prevent progression to irreversible Korsakoff
psychosis.
Question 3: During embryonic development, the midgut herniates into the umbilical
cord and later returns to the abdominal cavity while rotating. Failure of the midgut to
return to the abdomen results in which of the following congenital anomalies?
A. Gastroschisis B. Omphalocele C. Meckel diverticulum D. Hirschsprung disease
CORRECT ANSWER: B. Omphalocele
Rationale: Omphalocele results from persistent herniation of abdominal contents into the
umbilical cord due to failure of the midgut to return to the abdominal cavity during weeks
,10–11 of development. The herniated viscera are covered by a peritoneum-amnion
membrane.
Question 4: A 28-year-old woman presents with a 3-month history of intermittent
double vision and fatigable muscle weakness that worsens throughout the day.
Administration of edrophonium produces transient improvement in her symptoms.
Antibodies against which of the following structures are most likely responsible for
her condition?
A. Presynaptic voltage-gated calcium channels B. Postsynaptic nicotinic acetylcholine
receptors C. Muscle-specific kinase (MuSK) only D. Voltage-gated sodium channels
CORRECT ANSWER: B. Postsynaptic nicotinic acetylcholine receptors
Rationale: Myasthenia gravis is an autoimmune disorder caused by antibodies directed
against postsynaptic nicotinic acetylcholine receptors at the neuromuscular junction,
leading to receptor degradation and blockade. The edrophonium (Tensilon) test produces
transient improvement by inhibiting acetylcholinesterase.
Question 5: A 45-year-old man is diagnosed with a pheochromocytoma. Which of the
following enzymes catalyzes the rate-limiting step in the synthesis of the
catecholamines produced by this tumor?
A. Dopamine β-hydroxylase B. Phenylethanolamine N-methyltransferase C. Tyrosine
hydroxylase D. Dopa decarboxylase
CORRECT ANSWER: C. Tyrosine hydroxylase
Rationale: Tyrosine hydroxylase converts tyrosine to L-DOPA and is the rate-limiting enzyme
in catecholamine biosynthesis. Pheochromocytomas produce excess catecholamines
through this pathway.
Question 6: A 3-year-old boy is brought to the physician because of recurrent bacterial
infections and the absence of tonsils and palpable lymph nodes. Flow cytometry of
peripheral blood shows markedly decreased B cells but normal T-cell numbers.
Which of the following is the most likely diagnosis?
A. DiGeorge syndrome B. X-linked agammaglobulinemia C. Severe combined
immunodeficiency D. Chronic granulomatous disease
CORRECT ANSWER: B. X-linked agammaglobulinemia
Rationale: X-linked agammaglobulinemia (Bruton) results from a defect in Bruton tyrosine
kinase, preventing B-cell maturation. Patients have absent or very low B cells, absent
lymphoid tissue, and recurrent bacterial infections after maternal antibodies wane, while T-
cell numbers remain normal.
,Question 7: A 60-year-old woman with a history of rheumatoid arthritis has been taking
methotrexate for 8 years. She now has macrocytic anemia and elevated serum
homocysteine. Which of the following enzymatic reactions is most directly impaired
by her medication?
A. Conversion of methylmalonyl-CoA to succinyl-CoA B. Transfer of one-carbon units by
tetrahydrofolate C. Hydroxylation of proline in collagen D. Carboxylation of clotting factors
CORRECT ANSWER: B. Transfer of one-carbon units by tetrahydrofolate
Rationale: Methotrexate inhibits dihydrofolate reductase, depleting tetrahydrofolate.
Tetrahydrofolate is required as a carrier of one-carbon units for nucleotide synthesis and
regeneration of methionine from homocysteine, explaining the macrocytic anemia and
elevated homocysteine.
Question 8: A newborn is noted to have a left-sided flank mass. Imaging reveals fusion
of the inferior poles of the kidneys. Which of the following embryonic structures failed
to undergo normal development or migration?
A. Ureteric bud B. Metanephric mesenchyme C. Ascent and rotation of the kidneys D.
Mesonephric duct
CORRECT ANSWER: C. Ascent and rotation of the kidneys
Rationale: Horseshoe kidney results when the inferior poles of the kidneys fuse in the pelvis.
During ascent, the fused kidney is trapped under the inferior mesenteric artery, preventing
normal ascent and rotation.
Question 9: A 35-year-old man presents with a chronic cough and recurrent
pneumonia. Chest CT shows dilated bronchi with tram-track opacities. He also has a
long history of sinusitis and infertility. Which of the following is the most likely
underlying defect?
A. Defective chloride transport B. Immotile cilia due to dynein arm dysfunction C. Alpha-1
antitrypsin deficiency D. Hypersensitivity to Aspergillus
CORRECT ANSWER: B. Immotile cilia due to dynein arm dysfunction
Rationale: Kartagener syndrome (a form of primary ciliary dyskinesia) is caused by dynein
arm defects leading to immotile cilia. Clinical features include chronic sinusitis,
bronchiectasis, situs inversus (in some cases), and infertility due to immotile sperm.
Question 10: A 50-year-old man with longstanding type 2 diabetes mellitus has a
serum creatinine of 2.8 mg/dL and 4 g of proteinuria per day. Renal biopsy is most
likely to show which of the following findings?
, A. Linear IgG deposition along the glomerular basement membrane B. Nodular
glomerulosclerosis with Kimmelstiel-Wilson nodules C. Subepithelial humps on electron
microscopy D. Wire-loop lesions
CORRECT ANSWER: B. Nodular glomerulosclerosis with Kimmelstiel-Wilson nodules
Rationale: Diabetic nephropathy is characterized by mesangial expansion, basement-
membrane thickening, and pathognomonic Kimmelstiel-Wilson nodules (nodular
glomerulosclerosis). Heavy proteinuria is typical in advanced disease.
Question 11: A 22-year-old woman is started on isotretinoin for severe acne. She must
be counseled about the teratogenic risk of this medication because it disrupts which of
the following developmental processes?
A. Neural tube closure via folate antagonism B. Patterning of the limbs and pharyngeal
arches via retinoic acid excess C. Cardiac septation via impaired neural crest migration only
D. Renal ascent
CORRECT ANSWER: B. Patterning of the limbs and pharyngeal arches via retinoic acid
excess
Rationale: Isotretinoin is a potent teratogen that causes retinoic acid embryopathy,
characterized by craniofacial, cardiac, thymic, and central nervous system anomalies due to
disruption of Hox gene-mediated patterning and neural-crest migration.
Question 12: A 40-year-old woman has a serum calcium of 11.8 mg/dL, elevated
parathyroid hormone, and a neck mass. Which of the following is the most likely
mechanism of hypercalcemia?
A. Increased osteoblast activity B. Increased osteoclast activity mediated by RANKL C.
Decreased intestinal calcium absorption D. Increased renal calcium excretion
CORRECT ANSWER: B. Increased osteoclast activity mediated by RANKL
Rationale: Primary hyperparathyroidism increases PTH, which stimulates osteoblasts to
express RANKL. RANKL activates osteoclasts, increasing bone resorption and releasing
calcium into the serum.
Question 13: A 65-year-old man with a 40-pack-year smoking history presents with
proximal muscle weakness and fatigability that improves with repeated use.
Antibodies to which of the following are most likely present?
A. Postsynaptic acetylcholine receptors B. Presynaptic voltage-gated calcium channels C.
Muscle-specific kinase D. Titin
CORRECT ANSWER: B. Presynaptic voltage-gated calcium channels
