USMLE Step 1 practice exam (Form
182) Exam With Actual 120 Questions
& Verified Answers,Plus
Rationales/Expert Verified For
Guaranteed Pass Graded A+/
2025/2026 /Latest Update/Instant
Download Pdf
1. A 25-year-old man presents with recurrent infections. Laboratory studies show low
levels of IgG and IgA, but normal IgM. Which condition is most likely?
A) X-linked agammaglobulinemia
B) Hyper-IgM syndrome
C) Selective IgA deficiency
D) Common variable immunodeficiency
B) Hyper-IgM syndrome
Rationale: Hyper-IgM syndrome is characterized by defective class switching, resulting in
normal or elevated IgM with low IgG, IgA, and IgE. Patients are prone to recurrent
bacterial and opportunistic infections.
2. A patient presents with fatigue and pallor. Blood smear shows macrocytosis and
hypersegmented neutrophils. Which deficiency is most likely?
A) Iron
B) Folate
C) Vitamin B12
D) Vitamin D
C) Vitamin B12
Rationale: Vitamin B12 deficiency leads to megaloblastic anemia, presenting with
macrocytosis and hypersegmented neutrophils. Neurological symptoms may also occur.
3. Which enzyme is deficient in classic galactosemia?
A) Galactokinase
, B) Galactose-1-phosphate uridyltransferase
C) UDP-galactose epimerase
D) Lactase
B) Galactose-1-phosphate uridyltransferase
Rationale: Classic galactosemia results from galactose-1-phosphate uridyltransferase
deficiency, leading to accumulation of galactose-1-phosphate, causing hepatomegaly,
jaundice, and cataracts.
4. A 6-year-old boy presents with eczema, thrombocytopenia, and recurrent infections.
Which genetic defect is most consistent with this presentation?
A) BTK mutation
B) WAS gene mutation
C) ADA deficiency
D) RAG1 mutation
B) WAS gene mutation
Rationale: Wiskott-Aldrich syndrome presents with thrombocytopenia, eczema, and
recurrent infections, caused by a mutation in the WAS gene affecting cytoskeleton
rearrangement in hematopoietic cells.
5. Which part of the nephron is impermeable to water under all circumstances?
A) Proximal tubule
B) Descending loop of Henle
C) Ascending loop of Henle
D) Collecting duct
C) Ascending loop of Henle
Rationale: The thick ascending loop of Henle is impermeable to water, allowing for active
Na+, K+, and Cl- reabsorption, contributing to the medullary concentration gradient.
6. A patient has jaundice, dark urine, and pale stools. Lab results show high
unconjugated bilirubin. Which enzyme deficiency is likely?
A) UDP-glucuronyl transferase
B) Alcohol dehydrogenase
C) Glucose-6-phosphate dehydrogenase
D) Phenylalanine hydroxylase
A) UDP-glucuronyl transferase
Rationale: Gilbert and Crigler-Najjar syndromes are caused by deficiency of UDP-
glucuronyl transferase, impairing bilirubin conjugation and increasing unconjugated
bilirubin.
7. Which of the following is the rate-limiting enzyme in gluconeogenesis?
A) Glucose-6-phosphatase
, B) Fructose-1,6-bisphosphatase
C) Pyruvate carboxylase
D) PEP carboxykinase
B) Fructose-1,6-bisphosphatase
Rationale: Fructose-1,6-bisphosphatase catalyzes the conversion of fructose-1,6-
bisphosphate to fructose-6-phosphate and is the rate-limiting step in gluconeogenesis.
8. Which cardiac defect is most commonly associated with Down syndrome?
A) Tetralogy of Fallot
B) Transposition of the great arteries
C) Ventricular septal defect
D) Atrioventricular septal defect
D) Atrioventricular septal defect
Rationale: Down syndrome (Trisomy 21) frequently involves atrioventricular septal defects
due to endocardial cushion malformations.
9. Which neurotransmitter is decreased in Parkinson’s disease?
A) Dopamine
B) Serotonin
C) GABA
D) Acetylcholine
A) Dopamine
Rationale: Parkinson’s disease involves degeneration of dopaminergic neurons in the
substantia nigra pars compacta, leading to reduced dopamine levels and motor symptoms.
10. Which antibiotic inhibits bacterial cell wall synthesis by binding to D-Ala-D-Ala?
A) Ciprofloxacin
B) Penicillin
C) Tetracycline
D) Chloramphenicol
B) Penicillin
Rationale: Penicillin and other β-lactams inhibit transpeptidase enzymes that cross-link
peptidoglycan by binding D-Ala-D-Ala, weakening the bacterial cell wall.
11. A patient presents with polyuria and polydipsia. Lab shows hypernatremia and low
urine osmolality. Which hormone is deficient?
A) Aldosterone
B) ADH
C) Cortisol
D) Renin
182) Exam With Actual 120 Questions
& Verified Answers,Plus
Rationales/Expert Verified For
Guaranteed Pass Graded A+/
2025/2026 /Latest Update/Instant
Download Pdf
1. A 25-year-old man presents with recurrent infections. Laboratory studies show low
levels of IgG and IgA, but normal IgM. Which condition is most likely?
A) X-linked agammaglobulinemia
B) Hyper-IgM syndrome
C) Selective IgA deficiency
D) Common variable immunodeficiency
B) Hyper-IgM syndrome
Rationale: Hyper-IgM syndrome is characterized by defective class switching, resulting in
normal or elevated IgM with low IgG, IgA, and IgE. Patients are prone to recurrent
bacterial and opportunistic infections.
2. A patient presents with fatigue and pallor. Blood smear shows macrocytosis and
hypersegmented neutrophils. Which deficiency is most likely?
A) Iron
B) Folate
C) Vitamin B12
D) Vitamin D
C) Vitamin B12
Rationale: Vitamin B12 deficiency leads to megaloblastic anemia, presenting with
macrocytosis and hypersegmented neutrophils. Neurological symptoms may also occur.
3. Which enzyme is deficient in classic galactosemia?
A) Galactokinase
, B) Galactose-1-phosphate uridyltransferase
C) UDP-galactose epimerase
D) Lactase
B) Galactose-1-phosphate uridyltransferase
Rationale: Classic galactosemia results from galactose-1-phosphate uridyltransferase
deficiency, leading to accumulation of galactose-1-phosphate, causing hepatomegaly,
jaundice, and cataracts.
4. A 6-year-old boy presents with eczema, thrombocytopenia, and recurrent infections.
Which genetic defect is most consistent with this presentation?
A) BTK mutation
B) WAS gene mutation
C) ADA deficiency
D) RAG1 mutation
B) WAS gene mutation
Rationale: Wiskott-Aldrich syndrome presents with thrombocytopenia, eczema, and
recurrent infections, caused by a mutation in the WAS gene affecting cytoskeleton
rearrangement in hematopoietic cells.
5. Which part of the nephron is impermeable to water under all circumstances?
A) Proximal tubule
B) Descending loop of Henle
C) Ascending loop of Henle
D) Collecting duct
C) Ascending loop of Henle
Rationale: The thick ascending loop of Henle is impermeable to water, allowing for active
Na+, K+, and Cl- reabsorption, contributing to the medullary concentration gradient.
6. A patient has jaundice, dark urine, and pale stools. Lab results show high
unconjugated bilirubin. Which enzyme deficiency is likely?
A) UDP-glucuronyl transferase
B) Alcohol dehydrogenase
C) Glucose-6-phosphate dehydrogenase
D) Phenylalanine hydroxylase
A) UDP-glucuronyl transferase
Rationale: Gilbert and Crigler-Najjar syndromes are caused by deficiency of UDP-
glucuronyl transferase, impairing bilirubin conjugation and increasing unconjugated
bilirubin.
7. Which of the following is the rate-limiting enzyme in gluconeogenesis?
A) Glucose-6-phosphatase
, B) Fructose-1,6-bisphosphatase
C) Pyruvate carboxylase
D) PEP carboxykinase
B) Fructose-1,6-bisphosphatase
Rationale: Fructose-1,6-bisphosphatase catalyzes the conversion of fructose-1,6-
bisphosphate to fructose-6-phosphate and is the rate-limiting step in gluconeogenesis.
8. Which cardiac defect is most commonly associated with Down syndrome?
A) Tetralogy of Fallot
B) Transposition of the great arteries
C) Ventricular septal defect
D) Atrioventricular septal defect
D) Atrioventricular septal defect
Rationale: Down syndrome (Trisomy 21) frequently involves atrioventricular septal defects
due to endocardial cushion malformations.
9. Which neurotransmitter is decreased in Parkinson’s disease?
A) Dopamine
B) Serotonin
C) GABA
D) Acetylcholine
A) Dopamine
Rationale: Parkinson’s disease involves degeneration of dopaminergic neurons in the
substantia nigra pars compacta, leading to reduced dopamine levels and motor symptoms.
10. Which antibiotic inhibits bacterial cell wall synthesis by binding to D-Ala-D-Ala?
A) Ciprofloxacin
B) Penicillin
C) Tetracycline
D) Chloramphenicol
B) Penicillin
Rationale: Penicillin and other β-lactams inhibit transpeptidase enzymes that cross-link
peptidoglycan by binding D-Ala-D-Ala, weakening the bacterial cell wall.
11. A patient presents with polyuria and polydipsia. Lab shows hypernatremia and low
urine osmolality. Which hormone is deficient?
A) Aldosterone
B) ADH
C) Cortisol
D) Renin
