NBME 30 Exam Questions and
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1
Exam Section 1: Item 1 of 50
National Board of Medical Examiners®
Comprehensive Basic Science Self-Assessment
1. Shortly after delivery, a full-term male newborn is found to have black hair with a white
forelock. His mother, a brunette, also has a white forelock and wears hearing aids. Physical
examination shows heterochromia of irides. Otoacoustic emissions testing and
brain stem auditory evoked responses show bilateral sensorineural hearing loss. Which of
the following is the most likely cause of the findings in this patient?
A) Abnormal neural crest development
B) Abnormality of connexins
C) Deficiency of homogentisic acid oxidase activity
D) Deficiency of tyrosinase activity
E) Failure of internalization of melanin granules by keratinocytes
,F) Failure of melanosome transportation along dendrites—ANSWER-A.
Abnormal neural crest development leads to Waardenburg syndrome. Waardenburg
syndrome is a syndrome of patchy depigmentation of the skin, hair, irises, and cochlear
dysfunction that primarily illustrates an autosomal dominant inheritance pattern. Because of
genetic mutations of genes encoding transcription factors, neural crest cells do not properly
differentiate into melanoblasts (melanocyte precursors), or melanoblasts do not migrate to
their appropriate location. Patients typically have a white forelock and eyelashes,
depigmented skin patches, iridic heterochromia, and sensorineural deafness. The eyes may
also be laterally displaced. The clinical diagnosis may be confirmed with genetic testing.
Treatment includes audiologic evaluation and genetic consultation.
Incorrect Answers: B, C, D, E, and F.
An abnormality of connexins (Choice B) would lead to abnormal formation of the plasma
membrane channels of diverse cell types. Different combinations of sensorineural hearing
loss, ichthyosis, alopecia, and peripheral neuropathy may occur. Depigmentation
would be atypical.
Deficiency of homogentisic acid oxidase activity (Choice C) would lead to decreased
metabolism of the amino acids phenylalanine and tyrosine, which instead degrade into
homogentisic acid. Homogentisic acid accumulates in the skin and joints, causing increased
pigmentation and arthritis, respectively. Depigmentation would be atypical.
© 2026 Copyright. All Rights Reserved. This document is
protected by copyright law, Copyrighted By Brittie Donald
,Deficiency of tyrosinase activity (Choice D) occurs in oculocutaneous albinism, which
presents with uniformly hypopigmented hair and skin (versus the patchy depigmentation of
Waardenburg syndrome) and eye abnormalities (eg, iris hypopigmentation, refractive
errors, nystagmus). In tyrosinase deficiency, melanocytes are unable to synthesize melanin
from the amino acid tyrosine. Iridic heterochromia and sensorineural deafness would be
atypical.
Failure of internalization of melanin granules by keratinocytes (Choice E) as well as the
failure of melanosome transportation along dendrites (Choice F) would lead to decreased
pigmentation of keratinocytes, the primary cell type of the epidermis. These
abnormalities would likely lead to uniform depigmentation (versus the patchy
depigmentation of Waardenburg syndrome), and iridic heterochromia and sensorineural
hearing loss would be atypical.
Educational Objective: Waardenburg syndrome is a syndrome of patchy depigmentation of
the skin, hair, irises, and cochlear dysfunction that results from a defect in the differentiation
of neural crest cells into melanocytes. Patients typically present with a white
forelock and eyelashes, depigmented skin patches, iridic heterochromia, and sensorineural
hearing loss.
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Exam Section 1: Item 2 of 50
National Board of Medical Examiners®
Comprehensive Basic Science Self-Assessment
2. During an experiment, a solution of mixed fatty acids is injected into the duodenum of an
experimental animal. Under these conditions, the clearance rate of an intravenous glucose
load from the circulation is doubled. In contrast, an injection of an equal
volume amount of 0.9% saline into the duodenum has much less effect on the plasma
clearance rate of glucose. These findings are most likely caused by the secretion of which of
the following hormones?
A) Gastrin
B) Glucose-dependent insulinotropic peptide
C) Motilin
D) Secretin
E) Somatostatin—ANSWER-B.
© 2026 Copyright. All Rights Reserved. This document is
protected by copyright law, Copyrighted By Brittie Donald
Answers 100% PASS
1
Exam Section 1: Item 1 of 50
National Board of Medical Examiners®
Comprehensive Basic Science Self-Assessment
1. Shortly after delivery, a full-term male newborn is found to have black hair with a white
forelock. His mother, a brunette, also has a white forelock and wears hearing aids. Physical
examination shows heterochromia of irides. Otoacoustic emissions testing and
brain stem auditory evoked responses show bilateral sensorineural hearing loss. Which of
the following is the most likely cause of the findings in this patient?
A) Abnormal neural crest development
B) Abnormality of connexins
C) Deficiency of homogentisic acid oxidase activity
D) Deficiency of tyrosinase activity
E) Failure of internalization of melanin granules by keratinocytes
,F) Failure of melanosome transportation along dendrites—ANSWER-A.
Abnormal neural crest development leads to Waardenburg syndrome. Waardenburg
syndrome is a syndrome of patchy depigmentation of the skin, hair, irises, and cochlear
dysfunction that primarily illustrates an autosomal dominant inheritance pattern. Because of
genetic mutations of genes encoding transcription factors, neural crest cells do not properly
differentiate into melanoblasts (melanocyte precursors), or melanoblasts do not migrate to
their appropriate location. Patients typically have a white forelock and eyelashes,
depigmented skin patches, iridic heterochromia, and sensorineural deafness. The eyes may
also be laterally displaced. The clinical diagnosis may be confirmed with genetic testing.
Treatment includes audiologic evaluation and genetic consultation.
Incorrect Answers: B, C, D, E, and F.
An abnormality of connexins (Choice B) would lead to abnormal formation of the plasma
membrane channels of diverse cell types. Different combinations of sensorineural hearing
loss, ichthyosis, alopecia, and peripheral neuropathy may occur. Depigmentation
would be atypical.
Deficiency of homogentisic acid oxidase activity (Choice C) would lead to decreased
metabolism of the amino acids phenylalanine and tyrosine, which instead degrade into
homogentisic acid. Homogentisic acid accumulates in the skin and joints, causing increased
pigmentation and arthritis, respectively. Depigmentation would be atypical.
© 2026 Copyright. All Rights Reserved. This document is
protected by copyright law, Copyrighted By Brittie Donald
,Deficiency of tyrosinase activity (Choice D) occurs in oculocutaneous albinism, which
presents with uniformly hypopigmented hair and skin (versus the patchy depigmentation of
Waardenburg syndrome) and eye abnormalities (eg, iris hypopigmentation, refractive
errors, nystagmus). In tyrosinase deficiency, melanocytes are unable to synthesize melanin
from the amino acid tyrosine. Iridic heterochromia and sensorineural deafness would be
atypical.
Failure of internalization of melanin granules by keratinocytes (Choice E) as well as the
failure of melanosome transportation along dendrites (Choice F) would lead to decreased
pigmentation of keratinocytes, the primary cell type of the epidermis. These
abnormalities would likely lead to uniform depigmentation (versus the patchy
depigmentation of Waardenburg syndrome), and iridic heterochromia and sensorineural
hearing loss would be atypical.
Educational Objective: Waardenburg syndrome is a syndrome of patchy depigmentation of
the skin, hair, irises, and cochlear dysfunction that results from a defect in the differentiation
of neural crest cells into melanocytes. Patients typically present with a white
forelock and eyelashes, depigmented skin patches, iridic heterochromia, and sensorineural
hearing loss.
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2
Exam Section 1: Item 2 of 50
National Board of Medical Examiners®
Comprehensive Basic Science Self-Assessment
2. During an experiment, a solution of mixed fatty acids is injected into the duodenum of an
experimental animal. Under these conditions, the clearance rate of an intravenous glucose
load from the circulation is doubled. In contrast, an injection of an equal
volume amount of 0.9% saline into the duodenum has much less effect on the plasma
clearance rate of glucose. These findings are most likely caused by the secretion of which of
the following hormones?
A) Gastrin
B) Glucose-dependent insulinotropic peptide
C) Motilin
D) Secretin
E) Somatostatin—ANSWER-B.
© 2026 Copyright. All Rights Reserved. This document is
protected by copyright law, Copyrighted By Brittie Donald
