COMSAE Phase 1 Form 115 (2026/2027) ACTUAL EXAM
TEST BANK QUESTIONS AND CORRECT DETAILED
ANSWERS WITH RATIONALES
MOST TESTED QUESTIONS (VERIFIED
ANSWERS) |ALREADY GRADED A+||NEWEST VERSION
A 6-year-old boy presents with recurrent epistaxis. Physical exam shows telangiectasias on
the lips and mucosa. Which inheritance pattern best explains this condition?
a. X-linked recessive
b. Autosomal recessive
c. Mitochondrial
d. Autosomal dominant
✔️ Correct Answer: D. Autosomal dominant
Rationale: Recurrent epistaxis combined with mucosal and lip telangiectasias is highly
suggestive of Hereditary Hemorrhagic Telangiectasia (HHT), also called Osler-Weber-
Rendu syndrome. This disorder results from abnormal blood vessel formation, leading to
fragile vascular malformations that bleed easily. HHT is inherited in an autosomal
dominant pattern, meaning that a mutation in only one copy of the affected gene is
sufficient to cause disease. A child of an affected parent has a 50% chance of inheriting
the condition. Common clinical findings include recurrent spontaneous nosebleeds (most
common symptom), telangiectasias of lips, tongue, oral mucosa, and fingers,
arteriovenous malformations (AVMs) in organs such as the lungs, brain, and liver, and a
family history of similar bleeding symptoms. X-linked recessive disorders usually affect
males and are transmitted through carrier mothers; telangiectasias are not characteristic.
Autosomal recessive inheritance requires two mutated alleles and often appears without
vertical family transmission. Mitochondrial inheritance is passed only through the mother
and often affects high-energy tissues.
,Which enzyme deficiency causes phenylketonuria (PKU)?
a. Phenylalanine hydroxylase
b. Tyrosine aminotransferase
c. Homogentisate dioxygenase
d. Branched-chain α-ketoacid dehydrogenase
✔️ Correct Answer: A. Phenylalanine hydroxylase
Rationale: Classic Phenylketonuria (PKU) is caused by deficiency of phenylalanine
hydroxylase, the enzyme responsible for converting phenylalanine into tyrosine. When this
enzyme is deficient, phenylalanine accumulates in the blood, toxic metabolites build up
and damage the developing brain, and tyrosine becomes deficient, reducing
neurotransmitter and melanin synthesis. Classic symptoms include intellectual disability (if
untreated), developmental delay, seizures, a musty or "mousy" odor, and fair skin with
light hair due to decreased melanin production. PKU is detected through newborn
screening, and treatment involves a lifelong low-phenylalanine diet. Tyrosine
aminotransferase deficiency causes Tyrosinemia type II. Homogentisate dioxygenase
deficiency causes Alkaptonuria (dark urine, ochronosis). Branched-chain α-ketoacid
dehydrogenase deficiency causes Maple Syrup Urine Disease (MSUD).
A drug that prolongs the QT interval most likely blocks which cardiac channel?
a. Sodium channel (fast)
b. Delayed rectifier potassium channel (Iₖr)
c. L-type calcium channel
d. Funny current (If)
✔️ Correct Answer: B. Delayed rectifier potassium channel (Iₖr)
Rationale: The QT interval represents the total time for ventricular depolarization and
repolarization. QT prolongation usually occurs due to delayed ventricular repolarization,
most commonly from blockade of the rapid delayed rectifier potassium current (IKr). This
,potassium channel is critical during Phase 3 of the cardiac action potential, where
potassium exits the cell to repolarize ventricular myocytes. When IKr is blocked,
repolarization slows, the QT interval lengthens, and the risk increases for Torsades de
Pointes, a potentially fatal polymorphic ventricular tachycardia. Common drugs that
prolong QT include Class IA antiarrhythmics (quinidine), Class III antiarrhythmics (sotalol,
amiodarone), macrolides (azithromycin), fluoroquinolones, antipsychotics (haloperidol),
and ondansetron. Sodium channels affect depolarization and QRS width. L-type calcium
channels influence AV node conduction. The funny current (If) regulates SA node
automaticity.
During embryonic development, the neural crest gives rise to all of the following EXCEPT:
a. Melanocytes
b. Schwann cells
c. Adrenal medulla chromaffin cells
d. Hepatocytes
✔️ Correct Answer: D. Hepatocytes
Rationale: The neural crest is a transient embryologic structure that gives rise to many
important tissues remembered by the mnemonic "MOTEL PASS": Melanocytes,
Odontoblasts, Tracheoesophageal septum, Enterochromaffin cells, Laryngeal cartilage,
PNS ganglia, Adrenal medulla (chromaffin cells), Schwann cells, and Septum of heart
(conotruncal). Hepatocytes, however, arise from the endoderm, specifically the embryonic
foregut. Melanocytes are pigment-producing cells, Schwann cells myelinate peripheral
nerves, and adrenal medulla chromaffin cells produce catecholamines.
Which of the following bacteria is most commonly associated with dental caries?
a. Staphylococcus aureus
b. Streptococcus mutans
, c. Escherichia coli
d. Pseudomonas aeruginosa
✔️ Correct Answer: B. Streptococcus mutans
Rationale: Streptococcus mutans is the primary organism responsible for dental caries
(tooth decay). It metabolizes dietary sugars into acid, lowering oral pH and causing
demineralization of tooth enamel. The mechanism involves colonization of tooth surfaces,
fermentation of carbohydrates into acid, and acid dissolution of enamel hydroxyapatite,
leading to progressive destruction and cavities. Risk factors include frequent sugary
foods/drinks, poor oral hygiene, and reduced fluoride exposure. Staphylococcus aureus
causes skin infections, E. coli causes GI/UTI infections, and Pseudomonas causes
opportunistic infections.
In a patient with primary hyperaldosteronism (Conn syndrome), you would expect which
laboratory findings?
a. Hyperkalemia and metabolic acidosis
b. Hypokalemia and metabolic alkalosis
c. Hyponatremia and metabolic acidosis
d. Hyperkalemia and respiratory alkalosis
✔️ Correct Answer: B. Hypokalemia and metabolic alkalosis
Rationale: Primary hyperaldosteronism (Conn syndrome) involves excessive aldosterone
production, usually from an adrenal adenoma or adrenal hyperplasia. Aldosterone acts in
the distal nephron to increase sodium reabsorption, increase potassium excretion, and
increase hydrogen ion excretion. This produces hypokalemia (loss of potassium) and
metabolic alkalosis (loss of hydrogen ions). Patients may present with hypertension
resistant to treatment, muscle weakness, polyuria, and headaches. Laboratory findings
include elevated aldosterone, decreased renin, and possible mild hypernatremia.
The steep part of the oxyhemoglobin dissociation curve is important because:
TEST BANK QUESTIONS AND CORRECT DETAILED
ANSWERS WITH RATIONALES
MOST TESTED QUESTIONS (VERIFIED
ANSWERS) |ALREADY GRADED A+||NEWEST VERSION
A 6-year-old boy presents with recurrent epistaxis. Physical exam shows telangiectasias on
the lips and mucosa. Which inheritance pattern best explains this condition?
a. X-linked recessive
b. Autosomal recessive
c. Mitochondrial
d. Autosomal dominant
✔️ Correct Answer: D. Autosomal dominant
Rationale: Recurrent epistaxis combined with mucosal and lip telangiectasias is highly
suggestive of Hereditary Hemorrhagic Telangiectasia (HHT), also called Osler-Weber-
Rendu syndrome. This disorder results from abnormal blood vessel formation, leading to
fragile vascular malformations that bleed easily. HHT is inherited in an autosomal
dominant pattern, meaning that a mutation in only one copy of the affected gene is
sufficient to cause disease. A child of an affected parent has a 50% chance of inheriting
the condition. Common clinical findings include recurrent spontaneous nosebleeds (most
common symptom), telangiectasias of lips, tongue, oral mucosa, and fingers,
arteriovenous malformations (AVMs) in organs such as the lungs, brain, and liver, and a
family history of similar bleeding symptoms. X-linked recessive disorders usually affect
males and are transmitted through carrier mothers; telangiectasias are not characteristic.
Autosomal recessive inheritance requires two mutated alleles and often appears without
vertical family transmission. Mitochondrial inheritance is passed only through the mother
and often affects high-energy tissues.
,Which enzyme deficiency causes phenylketonuria (PKU)?
a. Phenylalanine hydroxylase
b. Tyrosine aminotransferase
c. Homogentisate dioxygenase
d. Branched-chain α-ketoacid dehydrogenase
✔️ Correct Answer: A. Phenylalanine hydroxylase
Rationale: Classic Phenylketonuria (PKU) is caused by deficiency of phenylalanine
hydroxylase, the enzyme responsible for converting phenylalanine into tyrosine. When this
enzyme is deficient, phenylalanine accumulates in the blood, toxic metabolites build up
and damage the developing brain, and tyrosine becomes deficient, reducing
neurotransmitter and melanin synthesis. Classic symptoms include intellectual disability (if
untreated), developmental delay, seizures, a musty or "mousy" odor, and fair skin with
light hair due to decreased melanin production. PKU is detected through newborn
screening, and treatment involves a lifelong low-phenylalanine diet. Tyrosine
aminotransferase deficiency causes Tyrosinemia type II. Homogentisate dioxygenase
deficiency causes Alkaptonuria (dark urine, ochronosis). Branched-chain α-ketoacid
dehydrogenase deficiency causes Maple Syrup Urine Disease (MSUD).
A drug that prolongs the QT interval most likely blocks which cardiac channel?
a. Sodium channel (fast)
b. Delayed rectifier potassium channel (Iₖr)
c. L-type calcium channel
d. Funny current (If)
✔️ Correct Answer: B. Delayed rectifier potassium channel (Iₖr)
Rationale: The QT interval represents the total time for ventricular depolarization and
repolarization. QT prolongation usually occurs due to delayed ventricular repolarization,
most commonly from blockade of the rapid delayed rectifier potassium current (IKr). This
,potassium channel is critical during Phase 3 of the cardiac action potential, where
potassium exits the cell to repolarize ventricular myocytes. When IKr is blocked,
repolarization slows, the QT interval lengthens, and the risk increases for Torsades de
Pointes, a potentially fatal polymorphic ventricular tachycardia. Common drugs that
prolong QT include Class IA antiarrhythmics (quinidine), Class III antiarrhythmics (sotalol,
amiodarone), macrolides (azithromycin), fluoroquinolones, antipsychotics (haloperidol),
and ondansetron. Sodium channels affect depolarization and QRS width. L-type calcium
channels influence AV node conduction. The funny current (If) regulates SA node
automaticity.
During embryonic development, the neural crest gives rise to all of the following EXCEPT:
a. Melanocytes
b. Schwann cells
c. Adrenal medulla chromaffin cells
d. Hepatocytes
✔️ Correct Answer: D. Hepatocytes
Rationale: The neural crest is a transient embryologic structure that gives rise to many
important tissues remembered by the mnemonic "MOTEL PASS": Melanocytes,
Odontoblasts, Tracheoesophageal septum, Enterochromaffin cells, Laryngeal cartilage,
PNS ganglia, Adrenal medulla (chromaffin cells), Schwann cells, and Septum of heart
(conotruncal). Hepatocytes, however, arise from the endoderm, specifically the embryonic
foregut. Melanocytes are pigment-producing cells, Schwann cells myelinate peripheral
nerves, and adrenal medulla chromaffin cells produce catecholamines.
Which of the following bacteria is most commonly associated with dental caries?
a. Staphylococcus aureus
b. Streptococcus mutans
, c. Escherichia coli
d. Pseudomonas aeruginosa
✔️ Correct Answer: B. Streptococcus mutans
Rationale: Streptococcus mutans is the primary organism responsible for dental caries
(tooth decay). It metabolizes dietary sugars into acid, lowering oral pH and causing
demineralization of tooth enamel. The mechanism involves colonization of tooth surfaces,
fermentation of carbohydrates into acid, and acid dissolution of enamel hydroxyapatite,
leading to progressive destruction and cavities. Risk factors include frequent sugary
foods/drinks, poor oral hygiene, and reduced fluoride exposure. Staphylococcus aureus
causes skin infections, E. coli causes GI/UTI infections, and Pseudomonas causes
opportunistic infections.
In a patient with primary hyperaldosteronism (Conn syndrome), you would expect which
laboratory findings?
a. Hyperkalemia and metabolic acidosis
b. Hypokalemia and metabolic alkalosis
c. Hyponatremia and metabolic acidosis
d. Hyperkalemia and respiratory alkalosis
✔️ Correct Answer: B. Hypokalemia and metabolic alkalosis
Rationale: Primary hyperaldosteronism (Conn syndrome) involves excessive aldosterone
production, usually from an adrenal adenoma or adrenal hyperplasia. Aldosterone acts in
the distal nephron to increase sodium reabsorption, increase potassium excretion, and
increase hydrogen ion excretion. This produces hypokalemia (loss of potassium) and
metabolic alkalosis (loss of hydrogen ions). Patients may present with hypertension
resistant to treatment, muscle weakness, polyuria, and headaches. Laboratory findings
include elevated aldosterone, decreased renin, and possible mild hypernatremia.
The steep part of the oxyhemoglobin dissociation curve is important because:
