COMSAE PHASE 1 FORM 115 ACTUAL EXAM
TEST BANK 200 QUESTIONS AND CORRECT
DETAILED ANSWERS WITH RATIONALES
(VERIFIED ANSWERS) + 100 MOST TESTED
|ALREADY GRADED A+||NEWEST VERSION
1. 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
Detailed Rationale:
Recurrent epistaxis (nosebleeds) combined with telangiectasias on the lips and
mucous membranes 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
• Family history of similar bleeding symptoms Why the other answers are
incorrect:
• A. X-linked recessive: Usually affects males and is transmitted through
carrier mothers (e.g., hemophilia); telangiectasias are not characteristic.
• B. Autosomal recessive: Requires two mutated alleles and often appears
without vertical family transmission.
• C. Mitochondrial: Passed only through the mother and often affects
highenergy tissues (neurologic/muscular systems).
High-yield takeaway:
Epistaxis + mucosal telangiectasias = think HHT → Autosomal dominant
inheritance.
,2. Which enzyme deficiency causes phenylketonuria (PKU)?
A. Phenylalanine hydroxylase
B. Tyrosine aminotransferase
C. Homogentisate dioxygenase
D. Branched-chain α-ketoacid dehydrogenase
Detailed 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
• Tyrosine becomes deficient, reducing neurotransmitter and melanin
synthesis
Classic symptoms include:
• Intellectual disability (if untreated)
• Developmental delay
, • Seizures
• Musty or “mousy” odor
• Fair skin and light hair (↓ melanin production)
PKU is detected through newborn screening, and treatment involves a lifelong
low-phenylalanine diet.
Why the other answers are incorrect:
• B. Tyrosine aminotransferase: Deficiency causes Tyrosinemia type II.
• C. Homogentisate dioxygenase: Deficiency causes Alkaptonuria (dark
urine, ochronosis).
• D. Branched-chain α-ketoacid dehydrogenase: Deficiency causes Maple
Syrup Urine Disease (MSUD).
High-yield takeaway:
PKU = Phenylalanine hydroxylase deficiency → ↑ phenylalanine, ↓ tyrosine.
3. A drug that prolongs QT interval most likely blocks which cardiac channel?
A. Sodium channel (fast)
B. Delayed rectifier potassium channel (Iₖr)
C. L-type calcium channel
TEST BANK 200 QUESTIONS AND CORRECT
DETAILED ANSWERS WITH RATIONALES
(VERIFIED ANSWERS) + 100 MOST TESTED
|ALREADY GRADED A+||NEWEST VERSION
1. 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
Detailed Rationale:
Recurrent epistaxis (nosebleeds) combined with telangiectasias on the lips and
mucous membranes 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
• Family history of similar bleeding symptoms Why the other answers are
incorrect:
• A. X-linked recessive: Usually affects males and is transmitted through
carrier mothers (e.g., hemophilia); telangiectasias are not characteristic.
• B. Autosomal recessive: Requires two mutated alleles and often appears
without vertical family transmission.
• C. Mitochondrial: Passed only through the mother and often affects
highenergy tissues (neurologic/muscular systems).
High-yield takeaway:
Epistaxis + mucosal telangiectasias = think HHT → Autosomal dominant
inheritance.
,2. Which enzyme deficiency causes phenylketonuria (PKU)?
A. Phenylalanine hydroxylase
B. Tyrosine aminotransferase
C. Homogentisate dioxygenase
D. Branched-chain α-ketoacid dehydrogenase
Detailed 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
• Tyrosine becomes deficient, reducing neurotransmitter and melanin
synthesis
Classic symptoms include:
• Intellectual disability (if untreated)
• Developmental delay
, • Seizures
• Musty or “mousy” odor
• Fair skin and light hair (↓ melanin production)
PKU is detected through newborn screening, and treatment involves a lifelong
low-phenylalanine diet.
Why the other answers are incorrect:
• B. Tyrosine aminotransferase: Deficiency causes Tyrosinemia type II.
• C. Homogentisate dioxygenase: Deficiency causes Alkaptonuria (dark
urine, ochronosis).
• D. Branched-chain α-ketoacid dehydrogenase: Deficiency causes Maple
Syrup Urine Disease (MSUD).
High-yield takeaway:
PKU = Phenylalanine hydroxylase deficiency → ↑ phenylalanine, ↓ tyrosine.
3. A drug that prolongs QT interval most likely blocks which cardiac channel?
A. Sodium channel (fast)
B. Delayed rectifier potassium channel (Iₖr)
C. L-type calcium channel
