ROBBINS BASIC PATHOLOGY
10TH EDITION
AUTHOR(S)VINAY KUMAR; ABUL K.
ABBAS; JON C. ASTER
TEST BANK
1
Reference
Ch. 1 — The Cell as a Unit of Health and Disease — The
Genome
Question Stem
A 42-year-old man is found to have a colorectal tumor with
microsatellite instability on molecular testing. Which genomic
defect best explains this finding and its contribution to
tumorigenesis?
Options
A. Defective nucleotide excision repair leading to accumulation
of bulky DNA adducts
B. Failure of mismatch repair resulting in accumulation of
,insertion/deletion errors in repeat sequences
C. Loss of homologous recombination causing large
chromosomal deletions
D. Increased base excision repair activity reducing single-base
errors
Correct Answer
B
Rationales
• Correct (B): Microsatellite instability arises when the DNA
mismatch repair system fails, permitting insertion/deletion
errors in short tandem repeats to persist and contributing
to mutator phenotype and tumor development.
• Incorrect (A): Nucleotide excision repair defects cause
sensitivity to bulky helix-distorting lesions (e.g., UV-
induced pyrimidine dimers), not classical microsatellite
instability.
• Incorrect (C): Loss of homologous recombination (e.g.,
BRCA defects) leads to large-scale chromosomal
abnormalities, not the small repeat-length changes
characterizing MSI.
• Incorrect (D): Increased base excision repair would reduce
single-base lesions; it would not produce microsatellite
instability.
,Teaching Point
Mismatch repair failure → microsatellite instability → mutator
phenotype in cancers.
Citation (simplified APA)
Kumar et al. (2021). Robbins Basic Pathology (10th Ed.). Ch. 1.
2
Reference
Ch. 1 — The Cell as a Unit of Health and Disease — The
Genome
Question Stem
A newborn screening finds an autosomal recessive metabolic
disorder caused by a single-base substitution producing a stop
codon in an essential enzyme. Which genomic mechanism most
likely produced this mutation?
Options
A. Frameshift mutation due to nucleotide insertion
B. Missense mutation from a single nucleotide change
C. Nonsense mutation from a single base substitution
D. Expansion of trinucleotide repeats
Correct Answer
C
Rationales
, • Correct (C): A single-base substitution that generates a
premature stop codon is a nonsense mutation, producing
truncated, usually nonfunctional proteins and often severe
enzyme deficiency.
• Incorrect (A): Frameshift mutations result from insertions
or deletions altering the reading frame, not from a single
base substitution that introduces a stop codon.
• Incorrect (B): A missense mutation changes one amino
acid but does not create an early stop codon.
• Incorrect (D): Trinucleotide repeat expansions increase
repeat number and cause diseases like Huntington disease
or fragile X; they are not single-base stop codon
substitutions.
Teaching Point
Nonsense mutation = premature stop codon → truncated,
typically nonfunctional protein.
Citation (simplified APA)
Kumar et al. (2021). Robbins Basic Pathology (10th Ed.). Ch. 1.
3
Reference
Ch. 1 — The Cell as a Unit of Health and Disease — The
Genome
10TH EDITION
AUTHOR(S)VINAY KUMAR; ABUL K.
ABBAS; JON C. ASTER
TEST BANK
1
Reference
Ch. 1 — The Cell as a Unit of Health and Disease — The
Genome
Question Stem
A 42-year-old man is found to have a colorectal tumor with
microsatellite instability on molecular testing. Which genomic
defect best explains this finding and its contribution to
tumorigenesis?
Options
A. Defective nucleotide excision repair leading to accumulation
of bulky DNA adducts
B. Failure of mismatch repair resulting in accumulation of
,insertion/deletion errors in repeat sequences
C. Loss of homologous recombination causing large
chromosomal deletions
D. Increased base excision repair activity reducing single-base
errors
Correct Answer
B
Rationales
• Correct (B): Microsatellite instability arises when the DNA
mismatch repair system fails, permitting insertion/deletion
errors in short tandem repeats to persist and contributing
to mutator phenotype and tumor development.
• Incorrect (A): Nucleotide excision repair defects cause
sensitivity to bulky helix-distorting lesions (e.g., UV-
induced pyrimidine dimers), not classical microsatellite
instability.
• Incorrect (C): Loss of homologous recombination (e.g.,
BRCA defects) leads to large-scale chromosomal
abnormalities, not the small repeat-length changes
characterizing MSI.
• Incorrect (D): Increased base excision repair would reduce
single-base lesions; it would not produce microsatellite
instability.
,Teaching Point
Mismatch repair failure → microsatellite instability → mutator
phenotype in cancers.
Citation (simplified APA)
Kumar et al. (2021). Robbins Basic Pathology (10th Ed.). Ch. 1.
2
Reference
Ch. 1 — The Cell as a Unit of Health and Disease — The
Genome
Question Stem
A newborn screening finds an autosomal recessive metabolic
disorder caused by a single-base substitution producing a stop
codon in an essential enzyme. Which genomic mechanism most
likely produced this mutation?
Options
A. Frameshift mutation due to nucleotide insertion
B. Missense mutation from a single nucleotide change
C. Nonsense mutation from a single base substitution
D. Expansion of trinucleotide repeats
Correct Answer
C
Rationales
, • Correct (C): A single-base substitution that generates a
premature stop codon is a nonsense mutation, producing
truncated, usually nonfunctional proteins and often severe
enzyme deficiency.
• Incorrect (A): Frameshift mutations result from insertions
or deletions altering the reading frame, not from a single
base substitution that introduces a stop codon.
• Incorrect (B): A missense mutation changes one amino
acid but does not create an early stop codon.
• Incorrect (D): Trinucleotide repeat expansions increase
repeat number and cause diseases like Huntington disease
or fragile X; they are not single-base stop codon
substitutions.
Teaching Point
Nonsense mutation = premature stop codon → truncated,
typically nonfunctional protein.
Citation (simplified APA)
Kumar et al. (2021). Robbins Basic Pathology (10th Ed.). Ch. 1.
3
Reference
Ch. 1 — The Cell as a Unit of Health and Disease — The
Genome
