NBME CBSE (USMLE STEP 1) NEWEST
2026 ACTUAL EXAM| NBME
COMPREHENSIVE BASIC SCIENCE
EXAMINATION WITH COMPLETE 200
REAL EXAM QUESTIONS AND CORRECT
VERIFIED ANSWERS/ GURANTEED
PASS/INSTANT DOWNLOAD
General Principles – Biochemistry & Genetics
1. A newborn develops jaundice, hepatomegaly, and
hypoglycemia after fasting. Liver biopsy reveals increased
glycogen with abnormal structure. Which enzyme is most
likely deficient?
A) Glucose-6-phosphatase
B) Debranching enzyme
C) Branching enzyme
D) Myophosphorylase
Answer: C – Branching enzyme deficiency (Andersen
disease/Glycogen Storage Disease Type IV) causes abnormal
glycogen with long, unbranched chains, leading to hepatomegaly
and liver failure.
, 2. A patient with Lesch-Nyhan syndrome has hyperuricemia
and self-mutilating behavior. Which enzyme is deficient?
A) Xanthine oxidase
B) Hypoxanthine-guanine phosphoribosyltransferase (HGPRT)
C) Adenosine deaminase
D) PRPP synthetase
Answer: B – HGPRT deficiency leads to increased purine synthesis
and uric acid production.
3. A 55-year-old man with alcohol use disorder presents with
confusion, ataxia, and ophthalmoplegia. Which vitamin
deficiency is most likely?
A) Vitamin B1 (thiamine)
B) Vitamin B3 (niacin)
C) Vitamin B6 (pyridoxine)
D) Vitamin B12
Answer: A – Wernicke encephalopathy (confusion, ataxia,
ophthalmoplegia) is caused by thiamine (B1) deficiency,
commonly seen in alcohol use disorder.
4. A newborn is noted to have a high-pitched cry,
microcephaly, and epicanthal folds. A chromosomal analysis
reveals a deletion on chromosome 5p. What is the diagnosis?
A) Down syndrome
B) Edwards syndrome
C) Patau syndrome
D) Cri-du-chat syndrome
, Answer: D – Cri-du-chat syndrome is caused by deletion of the
short arm of chromosome 5 (5p-) and is characterized by a high-
pitched cry, microcephaly, and epicanthal folds.
5. A patient with xerophthalmia and night blindness has low
serum retinol levels. Which form of vitamin A is essential for
the visual cycle in rod cells?
A) Retinoic acid
B) Retinal (retinaldehyde)
C) Retinyl ester
D) Beta-carotene
Answer: B – Retinal (11-cis-retinal) combines with opsin to form
rhodopsin in rod cells, essential for scotopic (low-light) vision.
Cardiovascular & Respiratory Physiology
6. A 60-year-old man presents with a painless, non-pulsatile
mass in the right groin that increases with coughing. It is
located below and lateral to the pubic tubercle. What type of
hernia is this?
A) Direct inguinal hernia
B) Indirect inguinal hernia
C) Femoral hernia
D) Ventral hernia
, Answer: B – Indirect inguinal hernias pass through the deep
inguinal ring and are located lateral to the inferior epigastric
vessels.
7. A 28-year-old man with a 3-year history of cocaine abuse
presents to the ED with shortness of breath. Exam shows
diminished pulses in the left upper extremity and a widened
aortic arch on CXR. What is the most likely diagnosis?
A) Myocardial infarction
B) Dissecting aneurysm
C) Pulmonary embolism
D) Cardiac tamponade
Answer: B – Aortic dissection is a known complication of cocaine
abuse due to sympathetic stimulation causing shear stress on the
aortic wall.
8. Which of the following best describes the effect of obesity
on expiratory reserve volume (ERV) and functional residual
capacity (FRC)?
A) Increase ERV & FRC
B) Decrease ERV & FRC
C) No change
D) Increase ERV, decrease FRC
Answer: B – Obesity decreases both ERV and FRC due to reduced
chest wall compliance and increased abdominal pressure.
9. Pulsus paradoxus (a >10 mmHg drop in systolic BP during
inspiration) is classically associated with which condition?
2026 ACTUAL EXAM| NBME
COMPREHENSIVE BASIC SCIENCE
EXAMINATION WITH COMPLETE 200
REAL EXAM QUESTIONS AND CORRECT
VERIFIED ANSWERS/ GURANTEED
PASS/INSTANT DOWNLOAD
General Principles – Biochemistry & Genetics
1. A newborn develops jaundice, hepatomegaly, and
hypoglycemia after fasting. Liver biopsy reveals increased
glycogen with abnormal structure. Which enzyme is most
likely deficient?
A) Glucose-6-phosphatase
B) Debranching enzyme
C) Branching enzyme
D) Myophosphorylase
Answer: C – Branching enzyme deficiency (Andersen
disease/Glycogen Storage Disease Type IV) causes abnormal
glycogen with long, unbranched chains, leading to hepatomegaly
and liver failure.
, 2. A patient with Lesch-Nyhan syndrome has hyperuricemia
and self-mutilating behavior. Which enzyme is deficient?
A) Xanthine oxidase
B) Hypoxanthine-guanine phosphoribosyltransferase (HGPRT)
C) Adenosine deaminase
D) PRPP synthetase
Answer: B – HGPRT deficiency leads to increased purine synthesis
and uric acid production.
3. A 55-year-old man with alcohol use disorder presents with
confusion, ataxia, and ophthalmoplegia. Which vitamin
deficiency is most likely?
A) Vitamin B1 (thiamine)
B) Vitamin B3 (niacin)
C) Vitamin B6 (pyridoxine)
D) Vitamin B12
Answer: A – Wernicke encephalopathy (confusion, ataxia,
ophthalmoplegia) is caused by thiamine (B1) deficiency,
commonly seen in alcohol use disorder.
4. A newborn is noted to have a high-pitched cry,
microcephaly, and epicanthal folds. A chromosomal analysis
reveals a deletion on chromosome 5p. What is the diagnosis?
A) Down syndrome
B) Edwards syndrome
C) Patau syndrome
D) Cri-du-chat syndrome
, Answer: D – Cri-du-chat syndrome is caused by deletion of the
short arm of chromosome 5 (5p-) and is characterized by a high-
pitched cry, microcephaly, and epicanthal folds.
5. A patient with xerophthalmia and night blindness has low
serum retinol levels. Which form of vitamin A is essential for
the visual cycle in rod cells?
A) Retinoic acid
B) Retinal (retinaldehyde)
C) Retinyl ester
D) Beta-carotene
Answer: B – Retinal (11-cis-retinal) combines with opsin to form
rhodopsin in rod cells, essential for scotopic (low-light) vision.
Cardiovascular & Respiratory Physiology
6. A 60-year-old man presents with a painless, non-pulsatile
mass in the right groin that increases with coughing. It is
located below and lateral to the pubic tubercle. What type of
hernia is this?
A) Direct inguinal hernia
B) Indirect inguinal hernia
C) Femoral hernia
D) Ventral hernia
, Answer: B – Indirect inguinal hernias pass through the deep
inguinal ring and are located lateral to the inferior epigastric
vessels.
7. A 28-year-old man with a 3-year history of cocaine abuse
presents to the ED with shortness of breath. Exam shows
diminished pulses in the left upper extremity and a widened
aortic arch on CXR. What is the most likely diagnosis?
A) Myocardial infarction
B) Dissecting aneurysm
C) Pulmonary embolism
D) Cardiac tamponade
Answer: B – Aortic dissection is a known complication of cocaine
abuse due to sympathetic stimulation causing shear stress on the
aortic wall.
8. Which of the following best describes the effect of obesity
on expiratory reserve volume (ERV) and functional residual
capacity (FRC)?
A) Increase ERV & FRC
B) Decrease ERV & FRC
C) No change
D) Increase ERV, decrease FRC
Answer: B – Obesity decreases both ERV and FRC due to reduced
chest wall compliance and increased abdominal pressure.
9. Pulsus paradoxus (a >10 mmHg drop in systolic BP during
inspiration) is classically associated with which condition?
