NBME 27 EDU OBJ Exam
Questions and Answers 100%
PASS
1
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
© 2026 Copyright. All Rights Reserved. This document is
protected by copyright law, Copyrighted By Brittie Donald
,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 active steroid. Examples include forming unconjugated
dehydroepiandrosterone,
estrone, pregnenolone, and cholesterol. Deficiency in this enzyme may congenitally manifest
as X-linked ichthyosis, characterized by hyperkeratosis, rashes, and scaly skin caused by
accumulation of cholesterol sulfate in the skin, resulting in impaired fluidity of the plasma
membrane and adhesion between cells.
Zinc finger transcription factor Wilms tumor 1 (Choice E) is a tumor suppressor gene on
chromosome 11. Nephroblastoma is the most common renal malignancy in childhood
caused by
, mutations in tumor suppressor genes WT1 or WT2. It is characterized by a large, often
palpable, unilateral flank mass and hematuria.—ANSWER-Objective: 5a-Reductase catalyzes
the metabolism of testosterone to DHT. Individuals with 5a-reductase deficiency exhibit
decreased concentrations of DHT and impaired virilization
of the male urogenital tract. Individuals with 5a-reductase deficiency appear phenotypically
female externally or may have ambiguous external genitalia, with normal male internal
genitalia.
II
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Exam Section 1: Item 2 of 50
National Board of Medical Examiners'
Comprehensive Basic Science Self-Assessment
© 2026 Copyright. All Rights Reserved. This document is
protected by copyright law, Copyrighted By Brittie Donald
Questions and Answers 100%
PASS
1
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
© 2026 Copyright. All Rights Reserved. This document is
protected by copyright law, Copyrighted By Brittie Donald
,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 active steroid. Examples include forming unconjugated
dehydroepiandrosterone,
estrone, pregnenolone, and cholesterol. Deficiency in this enzyme may congenitally manifest
as X-linked ichthyosis, characterized by hyperkeratosis, rashes, and scaly skin caused by
accumulation of cholesterol sulfate in the skin, resulting in impaired fluidity of the plasma
membrane and adhesion between cells.
Zinc finger transcription factor Wilms tumor 1 (Choice E) is a tumor suppressor gene on
chromosome 11. Nephroblastoma is the most common renal malignancy in childhood
caused by
, mutations in tumor suppressor genes WT1 or WT2. It is characterized by a large, often
palpable, unilateral flank mass and hematuria.—ANSWER-Objective: 5a-Reductase catalyzes
the metabolism of testosterone to DHT. Individuals with 5a-reductase deficiency exhibit
decreased concentrations of DHT and impaired virilization
of the male urogenital tract. Individuals with 5a-reductase deficiency appear phenotypically
female externally or may have ambiguous external genitalia, with normal male internal
genitalia.
II
Next
Score Report
Lab Values
Calculator
Help
Pause
2
Exam Section 1: Item 2 of 50
National Board of Medical Examiners'
Comprehensive Basic Science Self-Assessment
© 2026 Copyright. All Rights Reserved. This document is
protected by copyright law, Copyrighted By Brittie Donald
