2025 NBME 27 ACTUAL EXAM WITH
COMPLETE QUESTIONS AND CORRECT
ANSWERS RATED A+
Exam Section 1: Item 1 of 50
National Board of Medical Examiners'
Comprehensive Basic Science Self-Assessment
1. A 40-year-old woman at 5 months' gestation comes to the
physician for amniocentesis. Results show a normal 46,XY
karyotype of the fetus. Four months later, the newborn is
delivered and
examination shows a female phenotype with mild clitoral
enlargement. Ultrasonography shows the presence of male but
not female genital ducts. This newborn most likely has a mutation
of
the gene of which of the following factors?
A) Anti-paramesonephric (müllerian) hormone
B) 5a-Reductase
C) SRY protein
D) Steroid sulfatase
E) Zinc finger transcription factor Wilms tumor 1 Correct Answer
B.
5a-Reductase is an enzyme that catalyzes the metabolism of
testosterone to dihydrotestosterone (DHT). Testosterone
promotes the development of the mesonephric (wolffian) duct that
develops
,into the seminal vesicles, epididymis, vas deferens, and
ejaculatory duct. DHT promotes the development of male external
genitalia and the prostate from the genital tubercle and urogenital
sinus. Individuals with 5a-reductase deficiency have defective
conversion of testosterone to DHT, leading to decreased
concentrations of DHT and impaired virilization of the male
urogenital tract.
Individuals with 5a-reductase deficiency therefore appear
phenotypically female externally or may have ambiguous external
genitalia. Individuals have normal male internal genitalia as a
result of
normal concentrations of testosterone.
InCorrect Answers: A, C, D, and E.
Anti-paramesonephric (müllerian) hormone (Choice A) or
müllerian inhibiting factor (MIF) is secreted by Sertoli cells and
suppresses the development of the paramesonephric (müllerian)
duct
that would have developed into female internal genital structures
such as the fallopian tubes, uterus, and upper vagina.
The SRY gene is located on the Y chromosome and is
responsible for producing testis-determining factor, also known as
the SRY protein (Choice C), for testes development. Following
testes
development, hormones secreted by Sertoli cells (MIF) and
Leydig cells (testosterone and DHT) promote the development of
male internal and external genitalia and suppress the
development
,of female structures. SRY gene translocation can occur during
recombination in which the SRY gene on the Y chromosome
becomes part of the X chromosome, leading to an XX embryo
developing male characteristics.
Steroid sulfatase (Choice D) is an enzyme that catalyzes the
conversion of sulfated steroid precursors to the
2
Exam Section 1: Item 2 of 50
National Board of Medical Examiners'
Comprehensive Basic Science Self-Assessment
2. A 16-year-old girl with cystic fibrosis is brought to the physician
because of a 3-week history of generalized weakness, numbness
and tingling of her arms and legs, and difficulty walking. She
has not adhered to her medication regimen during the past 6
months. She appears alert and oriented. Her vital signs are within
normal limits. Physical examination shows bilateral weakness
and decreased deep tendon reflexes in the upper and lower
extremities. She walks with an ataxic gait. The most likely cause
of these findings is a deficiency of which of the following?
A) Folic acid
B) Vitamin A
C) Vitamin B, (pyridoxine)
D) Vitamin D
E) Vitamin E Correct Answer E.
, Vitamin E is an antioxidant that protects erythrocytes and cells
from free radical damage. Deficiency may present with hemolytic
anemia and generalized muscle weakness. It can have a similar
presentation to vitamin B12 (cobalamin) deficiency with posterior
column and spinocerebellar tract demyelination. In contrast to
vitamin B12 deficiency, patients do not have megaloblastic
anemia,
hypersegmented neutrophils, or increased serum methylmalonic
acid concentrations. On peripheral smear, patients with vitamin E
deficiency may have acanthocytosis.
InCorrect Answers: A, B, C, and D.
Folic acid (Choice A) is converted to tetrahydrofolic acid and used
as a coenzyme in the synthesis of nucleotides and nucleosides.
Folate is contained in leafy vegetables and absorbed in the
jejunum. Folate deficiency is often seen in patients with
malnutrition, alcoholism, and patients taking anti-folate
medications (eg, phenytoin, methotrexate). Megaloblastic anemia
occurs in the
setting of impaired DNA synthesis.
Vitamin A (Choice B) is an antioxidant necessary for differentiation
of epithelial cells into specialized tissue. Deficiency is
characterized by ocular manifestations including night blindness,
corneal
degeneration, Bitot spots on the conjunctiva, dry skin, and
immunosuppression.
Vitamin B6 (pyridoxine) (Choice C) deficiency limits synthesis of
histamine, hemoglobin, and neurotransmitters including
epinephrine, norepinephrine, dopamine, serotonin, and GABA.
Deficiency
COMPLETE QUESTIONS AND CORRECT
ANSWERS RATED A+
Exam Section 1: Item 1 of 50
National Board of Medical Examiners'
Comprehensive Basic Science Self-Assessment
1. A 40-year-old woman at 5 months' gestation comes to the
physician for amniocentesis. Results show a normal 46,XY
karyotype of the fetus. Four months later, the newborn is
delivered and
examination shows a female phenotype with mild clitoral
enlargement. Ultrasonography shows the presence of male but
not female genital ducts. This newborn most likely has a mutation
of
the gene of which of the following factors?
A) Anti-paramesonephric (müllerian) hormone
B) 5a-Reductase
C) SRY protein
D) Steroid sulfatase
E) Zinc finger transcription factor Wilms tumor 1 Correct Answer
B.
5a-Reductase is an enzyme that catalyzes the metabolism of
testosterone to dihydrotestosterone (DHT). Testosterone
promotes the development of the mesonephric (wolffian) duct that
develops
,into the seminal vesicles, epididymis, vas deferens, and
ejaculatory duct. DHT promotes the development of male external
genitalia and the prostate from the genital tubercle and urogenital
sinus. Individuals with 5a-reductase deficiency have defective
conversion of testosterone to DHT, leading to decreased
concentrations of DHT and impaired virilization of the male
urogenital tract.
Individuals with 5a-reductase deficiency therefore appear
phenotypically female externally or may have ambiguous external
genitalia. Individuals have normal male internal genitalia as a
result of
normal concentrations of testosterone.
InCorrect Answers: A, C, D, and E.
Anti-paramesonephric (müllerian) hormone (Choice A) or
müllerian inhibiting factor (MIF) is secreted by Sertoli cells and
suppresses the development of the paramesonephric (müllerian)
duct
that would have developed into female internal genital structures
such as the fallopian tubes, uterus, and upper vagina.
The SRY gene is located on the Y chromosome and is
responsible for producing testis-determining factor, also known as
the SRY protein (Choice C), for testes development. Following
testes
development, hormones secreted by Sertoli cells (MIF) and
Leydig cells (testosterone and DHT) promote the development of
male internal and external genitalia and suppress the
development
,of female structures. SRY gene translocation can occur during
recombination in which the SRY gene on the Y chromosome
becomes part of the X chromosome, leading to an XX embryo
developing male characteristics.
Steroid sulfatase (Choice D) is an enzyme that catalyzes the
conversion of sulfated steroid precursors to the
2
Exam Section 1: Item 2 of 50
National Board of Medical Examiners'
Comprehensive Basic Science Self-Assessment
2. A 16-year-old girl with cystic fibrosis is brought to the physician
because of a 3-week history of generalized weakness, numbness
and tingling of her arms and legs, and difficulty walking. She
has not adhered to her medication regimen during the past 6
months. She appears alert and oriented. Her vital signs are within
normal limits. Physical examination shows bilateral weakness
and decreased deep tendon reflexes in the upper and lower
extremities. She walks with an ataxic gait. The most likely cause
of these findings is a deficiency of which of the following?
A) Folic acid
B) Vitamin A
C) Vitamin B, (pyridoxine)
D) Vitamin D
E) Vitamin E Correct Answer E.
, Vitamin E is an antioxidant that protects erythrocytes and cells
from free radical damage. Deficiency may present with hemolytic
anemia and generalized muscle weakness. It can have a similar
presentation to vitamin B12 (cobalamin) deficiency with posterior
column and spinocerebellar tract demyelination. In contrast to
vitamin B12 deficiency, patients do not have megaloblastic
anemia,
hypersegmented neutrophils, or increased serum methylmalonic
acid concentrations. On peripheral smear, patients with vitamin E
deficiency may have acanthocytosis.
InCorrect Answers: A, B, C, and D.
Folic acid (Choice A) is converted to tetrahydrofolic acid and used
as a coenzyme in the synthesis of nucleotides and nucleosides.
Folate is contained in leafy vegetables and absorbed in the
jejunum. Folate deficiency is often seen in patients with
malnutrition, alcoholism, and patients taking anti-folate
medications (eg, phenytoin, methotrexate). Megaloblastic anemia
occurs in the
setting of impaired DNA synthesis.
Vitamin A (Choice B) is an antioxidant necessary for differentiation
of epithelial cells into specialized tissue. Deficiency is
characterized by ocular manifestations including night blindness,
corneal
degeneration, Bitot spots on the conjunctiva, dry skin, and
immunosuppression.
Vitamin B6 (pyridoxine) (Choice C) deficiency limits synthesis of
histamine, hemoglobin, and neurotransmitters including
epinephrine, norepinephrine, dopamine, serotonin, and GABA.
Deficiency
