Page 1 of 84
COMSAE PHASE 1 FORM EXAM WITH VERIFIED ANSWERS
DETAILED RATIONALES GRADED A+
COMSAE Phase 1 Form 113
Section 1: Foundational Biomedical Sciences (Questions 1–25)
1. A 6-month-old infant presents with failure to thrive, hypotonia, and a musty odor to the
urine. Laboratory tests reveal elevated levels of phenylalanine. Which enzyme is most likely
deficient in this patient?
A. Tyrosinase
B. Phenylalanine hydroxylase
C. Homogentisate oxidase
D. Branched-chain alpha-ketoacid dehydrogenase
Rationale: B. The presentation is classic for phenylketonuria (PKU), which is caused by a
deficiency of phenylalanine hydroxylase, the enzyme responsible for converting
phenylalanine to tyrosine.
2. A 45-year-old male presents with sudden onset of severe abdominal pain, vomiting, and a
history of recurrent pancreatitis. Genetic testing reveals a mutation in the CFTR gene. Which
of the following is the most likely diagnosis?
A. Cystic fibrosis
B. Alpha-1 antitrypsin deficiency
C. Hereditary hemochromatosis
D. Wilson's disease
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Rationale: A. Cystic fibrosis is caused by mutations in the CFTR gene, which leads to defective
chloride transport and thick secretions, often presenting with pancreatitis and other systemic
complications in adulthood.
3. A 2-year-old child is brought to the emergency department with lethargy, vomiting, and
hepatomegaly. Laboratory findings reveal hypoglycemia, hyperammonemia, and elevated
liver enzymes. Which metabolic disorder is most likely?
A. Maple syrup urine disease
B. Galactosemia
C. Glycogen storage disease type I (von Gierke disease)
D. Fructose intolerance
Rationale: C. Glycogen storage disease type I (von Gierke disease) is caused by a deficiency of
glucose-6-phosphatase, leading to severe hypoglycemia, hepatomegaly, and
hyperammonemia due to impaired gluconeogenesis.
4. A 30-year-old female presents with recurrent kidney stones and is found to have elevated
urinary oxalate levels. Genetic testing reveals a defect in the AGXT gene. Which enzyme is
most likely deficient?
A. Alanine-glyoxylate aminotransferase
B. Xanthine oxidase
C. Adenine phosphoribosyltransferase
D. Hypoxanthine-guanine phosphoribosyltransferase
Rationale: A. Primary hyperoxaluria type 1 is caused by a deficiency of alanine-glyoxylate
aminotransferase (AGT), leading to increased oxalate production and recurrent calcium
oxalate kidney stones.
5. A 55-year-old male with a history of alcohol abuse presents with severe abdominal pain,
fever, and hypotension. Laboratory tests show elevated amylase and lipase. Which of the
following is the most likely underlying mechanism?
A. Premature activation of trypsinogen within the pancreas
B. Deficiency of alpha-1 antitrypsin
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C. Autoimmune destruction of pancreatic beta cells
D. Gallstone obstruction of the pancreatic duct
Rationale: A. Acute pancreatitis is most commonly caused by premature activation of
trypsinogen within the pancreas, leading to autodigestion. Alcohol abuse is a major risk
factor.
6. A 25-year-old female presents with fatigue, pallor, and jaundice. Laboratory tests reveal a
hemoglobin level of 8 g/dL, elevated reticulocyte count, and a positive indirect Coombs test.
Which type of anemia is most likely?
A. Iron deficiency anemia
B. Anemia of chronic disease
C. Autoimmune hemolytic anemia
D. Thalassemia
Rationale: C. A positive indirect Coombs test indicates the presence of antibodies against red
blood cells, which is characteristic of autoimmune hemolytic anemia.
7. A 60-year-old male with a history of chronic obstructive pulmonary disease (COPD)
presents with worsening dyspnea. Arterial blood gas reveals a pH of 7.32, PaCO2 of 55 mm
Hg, and HCO3 of 28 mEq/L. Which acid-base disturbance is present?
A. Respiratory acidosis with metabolic compensation
B. Respiratory alkalosis with metabolic compensation
C. Metabolic acidosis with respiratory compensation
D. Metabolic alkalosis with respiratory compensation
Rationale: A. The elevated PaCO2 indicates respiratory acidosis. The elevated HCO3 indicates
metabolic compensation, which occurs in chronic respiratory acidosis.
8. A 35-year-old female presents with recurrent infections, easy bruising, and gingival
bleeding. Laboratory tests reveal a prolonged bleeding time and normal platelet count. Which
of the following is the most likely diagnosis?
A. Hemophilia A
B. von Willebrand disease
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C. Idiopathic thrombocytopenic purpura
D. Vitamin K deficiency
Rationale: B. von Willebrand disease is the most common inherited bleeding disorder,
characterized by a prolonged bleeding time and normal platelet count. It is caused by a
deficiency or dysfunction of von Willebrand factor.
9. A 50-year-old male presents with progressive weakness, weight loss, and
hyperpigmentation of the skin. Laboratory tests reveal hyponatremia, hyperkalemia, and
hypoglycemia. Which of the following is the most likely diagnosis?
A. Addison's disease
B. Cushing's syndrome
C. Conn's syndrome
D. Pheochromocytoma
Rationale: A. Addison's disease (primary adrenal insufficiency) is characterized by deficiency
of cortisol and aldosterone, leading to hyponatremia, hyperkalemia, hypoglycemia, and
hyperpigmentation due to elevated ACTH.
10. A 45-year-old female with a history of breast cancer presents with bone pain and
hypercalcemia. Which of the following is the most likely mechanism of hypercalcemia in this
patient?
A. Increased parathyroid hormone secretion
B. Increased production of parathyroid hormone-related peptide (PTHrP)
C. Increased vitamin D activation
D. Decreased renal calcium excretion
Rationale: B. Malignancy-associated hypercalcemia is often mediated by PTHrP, which is
produced by tumor cells and acts like PTH to increase bone resorption and renal calcium
reabsorption.
11. A 28-year-old male presents with fever, chills, and a heart murmur. Blood cultures grow
Staphylococcus aureus. Which of the following is the most likely source of infection?
A. Intravenous drug use
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COMSAE PHASE 1 FORM EXAM WITH VERIFIED ANSWERS
DETAILED RATIONALES GRADED A+
COMSAE Phase 1 Form 113
Section 1: Foundational Biomedical Sciences (Questions 1–25)
1. A 6-month-old infant presents with failure to thrive, hypotonia, and a musty odor to the
urine. Laboratory tests reveal elevated levels of phenylalanine. Which enzyme is most likely
deficient in this patient?
A. Tyrosinase
B. Phenylalanine hydroxylase
C. Homogentisate oxidase
D. Branched-chain alpha-ketoacid dehydrogenase
Rationale: B. The presentation is classic for phenylketonuria (PKU), which is caused by a
deficiency of phenylalanine hydroxylase, the enzyme responsible for converting
phenylalanine to tyrosine.
2. A 45-year-old male presents with sudden onset of severe abdominal pain, vomiting, and a
history of recurrent pancreatitis. Genetic testing reveals a mutation in the CFTR gene. Which
of the following is the most likely diagnosis?
A. Cystic fibrosis
B. Alpha-1 antitrypsin deficiency
C. Hereditary hemochromatosis
D. Wilson's disease
1|Page
,Page 2 of 84
Rationale: A. Cystic fibrosis is caused by mutations in the CFTR gene, which leads to defective
chloride transport and thick secretions, often presenting with pancreatitis and other systemic
complications in adulthood.
3. A 2-year-old child is brought to the emergency department with lethargy, vomiting, and
hepatomegaly. Laboratory findings reveal hypoglycemia, hyperammonemia, and elevated
liver enzymes. Which metabolic disorder is most likely?
A. Maple syrup urine disease
B. Galactosemia
C. Glycogen storage disease type I (von Gierke disease)
D. Fructose intolerance
Rationale: C. Glycogen storage disease type I (von Gierke disease) is caused by a deficiency of
glucose-6-phosphatase, leading to severe hypoglycemia, hepatomegaly, and
hyperammonemia due to impaired gluconeogenesis.
4. A 30-year-old female presents with recurrent kidney stones and is found to have elevated
urinary oxalate levels. Genetic testing reveals a defect in the AGXT gene. Which enzyme is
most likely deficient?
A. Alanine-glyoxylate aminotransferase
B. Xanthine oxidase
C. Adenine phosphoribosyltransferase
D. Hypoxanthine-guanine phosphoribosyltransferase
Rationale: A. Primary hyperoxaluria type 1 is caused by a deficiency of alanine-glyoxylate
aminotransferase (AGT), leading to increased oxalate production and recurrent calcium
oxalate kidney stones.
5. A 55-year-old male with a history of alcohol abuse presents with severe abdominal pain,
fever, and hypotension. Laboratory tests show elevated amylase and lipase. Which of the
following is the most likely underlying mechanism?
A. Premature activation of trypsinogen within the pancreas
B. Deficiency of alpha-1 antitrypsin
2|Page
,Page 3 of 84
C. Autoimmune destruction of pancreatic beta cells
D. Gallstone obstruction of the pancreatic duct
Rationale: A. Acute pancreatitis is most commonly caused by premature activation of
trypsinogen within the pancreas, leading to autodigestion. Alcohol abuse is a major risk
factor.
6. A 25-year-old female presents with fatigue, pallor, and jaundice. Laboratory tests reveal a
hemoglobin level of 8 g/dL, elevated reticulocyte count, and a positive indirect Coombs test.
Which type of anemia is most likely?
A. Iron deficiency anemia
B. Anemia of chronic disease
C. Autoimmune hemolytic anemia
D. Thalassemia
Rationale: C. A positive indirect Coombs test indicates the presence of antibodies against red
blood cells, which is characteristic of autoimmune hemolytic anemia.
7. A 60-year-old male with a history of chronic obstructive pulmonary disease (COPD)
presents with worsening dyspnea. Arterial blood gas reveals a pH of 7.32, PaCO2 of 55 mm
Hg, and HCO3 of 28 mEq/L. Which acid-base disturbance is present?
A. Respiratory acidosis with metabolic compensation
B. Respiratory alkalosis with metabolic compensation
C. Metabolic acidosis with respiratory compensation
D. Metabolic alkalosis with respiratory compensation
Rationale: A. The elevated PaCO2 indicates respiratory acidosis. The elevated HCO3 indicates
metabolic compensation, which occurs in chronic respiratory acidosis.
8. A 35-year-old female presents with recurrent infections, easy bruising, and gingival
bleeding. Laboratory tests reveal a prolonged bleeding time and normal platelet count. Which
of the following is the most likely diagnosis?
A. Hemophilia A
B. von Willebrand disease
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, Page 4 of 84
C. Idiopathic thrombocytopenic purpura
D. Vitamin K deficiency
Rationale: B. von Willebrand disease is the most common inherited bleeding disorder,
characterized by a prolonged bleeding time and normal platelet count. It is caused by a
deficiency or dysfunction of von Willebrand factor.
9. A 50-year-old male presents with progressive weakness, weight loss, and
hyperpigmentation of the skin. Laboratory tests reveal hyponatremia, hyperkalemia, and
hypoglycemia. Which of the following is the most likely diagnosis?
A. Addison's disease
B. Cushing's syndrome
C. Conn's syndrome
D. Pheochromocytoma
Rationale: A. Addison's disease (primary adrenal insufficiency) is characterized by deficiency
of cortisol and aldosterone, leading to hyponatremia, hyperkalemia, hypoglycemia, and
hyperpigmentation due to elevated ACTH.
10. A 45-year-old female with a history of breast cancer presents with bone pain and
hypercalcemia. Which of the following is the most likely mechanism of hypercalcemia in this
patient?
A. Increased parathyroid hormone secretion
B. Increased production of parathyroid hormone-related peptide (PTHrP)
C. Increased vitamin D activation
D. Decreased renal calcium excretion
Rationale: B. Malignancy-associated hypercalcemia is often mediated by PTHrP, which is
produced by tumor cells and acts like PTH to increase bone resorption and renal calcium
reabsorption.
11. A 28-year-old male presents with fever, chills, and a heart murmur. Blood cultures grow
Staphylococcus aureus. Which of the following is the most likely source of infection?
A. Intravenous drug use
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