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NBME 30 Exam Questions And Answers
|Latest 2025 | Guaranteed 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.
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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.
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
2|Page
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errors, nystagmus). In tyrosinase deficiency, melanocytes are unable to synthesize melanin
from the amino acid tyrosine. Iridic heterochromia and sensorineural deafnes
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.
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Glucose-dependent insulinotropic peptide (GIP) is secreted by K cells in the duodenum and
jejunum and functions to decrease gastric acid production and stimulate insulin release from
the pancreas. Its secretion is promoted by the presence of fatty acids, amino
acids, and intestinal glucose. While serum glucose also stimulates insulin secretion by the
pancreas, the effect of intraluminal glucose on GIP and subsequent insulin secretion leads to
increased concentrations of insulin compared to parenteral glucose
administration. Insulin promotes peripheral tissue uptake of glucose, glycolysis, glycogen
synthesis, protein synthesis, and fatty acid synthesis, resulting in decreased glucose
concentration in the serum.
Incorrect Answers: A, C, D, and E.
Gastrin (Choice A) is produced by G cells in the gastric antrum and stimulates parietal cells
within the gastric body to produce hydrochloric acid. Gastric acid has no effect on serum
glucose concentration.
Motilin (Choice C) is secreted by the small intestine and stimulates intestinal peristalsis. Motilin
receptors are targeted by erythromycin and metoclopramide, used therapeutically in
gastroparesis.
Secretin (Choice D) is produced by duodenal S cells. It promotes the release of bicarbonate-rich
pancreatic secretions and bile and inhibits gastric acid production.
Somatostatin (Choice E) is a regulatory peptide secreted by D cells of the pancreas and
gastrointestinal mucosa that inhibits gastric acid and pepsinogen secretion, gallbladder
contraction, and insulin and glucagon release. Somatostatin would have an indirect
4|Page
NBME 30 Exam Questions And Answers
|Latest 2025 | Guaranteed 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.
1|Page
, ©THESTAR 2025 ALL RIGHTS RESERVED 11:44 AM 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.
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
2|Page
, ©THESTAR 2025 ALL RIGHTS RESERVED 11:44 AM A+
errors, nystagmus). In tyrosinase deficiency, melanocytes are unable to synthesize melanin
from the amino acid tyrosine. Iridic heterochromia and sensorineural deafnes
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.
3|Page
, ©THESTAR 2025 ALL RIGHTS RESERVED 11:44 AM A+
Glucose-dependent insulinotropic peptide (GIP) is secreted by K cells in the duodenum and
jejunum and functions to decrease gastric acid production and stimulate insulin release from
the pancreas. Its secretion is promoted by the presence of fatty acids, amino
acids, and intestinal glucose. While serum glucose also stimulates insulin secretion by the
pancreas, the effect of intraluminal glucose on GIP and subsequent insulin secretion leads to
increased concentrations of insulin compared to parenteral glucose
administration. Insulin promotes peripheral tissue uptake of glucose, glycolysis, glycogen
synthesis, protein synthesis, and fatty acid synthesis, resulting in decreased glucose
concentration in the serum.
Incorrect Answers: A, C, D, and E.
Gastrin (Choice A) is produced by G cells in the gastric antrum and stimulates parietal cells
within the gastric body to produce hydrochloric acid. Gastric acid has no effect on serum
glucose concentration.
Motilin (Choice C) is secreted by the small intestine and stimulates intestinal peristalsis. Motilin
receptors are targeted by erythromycin and metoclopramide, used therapeutically in
gastroparesis.
Secretin (Choice D) is produced by duodenal S cells. It promotes the release of bicarbonate-rich
pancreatic secretions and bile and inhibits gastric acid production.
Somatostatin (Choice E) is a regulatory peptide secreted by D cells of the pancreas and
gastrointestinal mucosa that inhibits gastric acid and pepsinogen secretion, gallbladder
contraction, and insulin and glucagon release. Somatostatin would have an indirect
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