USMLE PRACTICE QUESTION #61
TOPIC: Hematology/genetics
Today’s question will test your understanding of a commonly tested hematology/genetics topic.
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A 6-year-old male was brought to the emergency department by his school nurse due to excessive bleeding. The bleeding was observed following a schoolyard incident resulting in the loss of a tooth, and despite attempts to apply pressure to the affected site, the bleeding has continued. Further evaluation of the patient's medical history revealed that his father and older sister have a known history of mucocutaneous bleeding.
His laboratory studies show:
Platelets: Within normal range
Bleeding time: Prolonged
Prothrombin time: Normal
Partial thromboplastin time: Prolonged
vWF antigen levels: Decreased
Factor VIII activity: Decreased
Ristocetin cofactor level: Low
The gene responsible for this boy’s condition is located on which of the following chromosomes?
A. Chromosome 4
B. Chromosome 8
C. Chromosome 10
D. Chromosome 12
E. Chromosome 15
F. Chromosome 18
Detailed Breakdown of Answers + Correct Answer Below ⏬
ANSWER + QUESTION BREAKDOWN
The mental model used to answer this question comes from our detailed test-taking skills masterclass. Here’s how to think through this question:
Step 1. Read the last line to determine what the question is asking: On which chromosome is the gene responsible for this condition located?
Step 2: Is this a first-, second-, or third-order question?
Answer: 3rd order: 1st. Diagnose with the disorder. 2nd. Know which gene is affected. 3rd. Know where the gene is located (chromosome).
Step 3. Read the vignette to gather information.
Step 4. Consider the question and ask yourself the most likely answer.
Step 5. Look at the answer choices and select the option most closely resembling your thoughts from “Step 4” above.
GENERAL ANALYSIS
The clinical presentation and laboratory findings in this case are consistent with von Willebrand disease (vWD), a bleeding disorder characterized by mucocutaneous bleeding, prolonged bleeding time, and decreased levels of von Willebrand factor (vWF) and factor VIII activity. The genetic information related to vWD involves the von Willebrand factor gene located on chromosome 12.
ANSWER CHOICES:
ANSWER CHOICE A: Chromosome 4
Explanation: Chromosome 4 is the origin of several gene anomalies, including:
Achondroplasia: A form of short-limbed dwarfism.
Huntington's Disease: A progressive brain disorder that causes uncontrolled movements, emotional problems, and loss of thinking ability (cognition).
Fibrodysplasia Ossificans Progressiva: A disorder in which muscle tissue and connective tissue such as tendons and ligaments are gradually replaced by bone.
ANSWER CHOICE B: Chromosome 8
Explanation: Chromosome 8 is the origin of several gene anomalies, including:
Burkitt Lymphoma: A type of cancer that affects the lymphatic system.
Langer-Giedion Syndrome: Characterized by multiple exostoses (bony growths) and distinctive facial features.
Cohen Syndrome: Characterized by developmental delay, microcephaly, and facial dysmorphism.
ANSWER CHOICE C: Chromosome 10
Explanation: Chromosome 10 is the origin of several gene anomalies, including:
Multiple Endocrine Neoplasia Type 2 (MEN2): A disorder that affects the endocrine glands, leading to tumors.
Pheochromocytoma: A rare tumor of adrenal gland tissue.
Congenital Adrenal Hyperplasia: A group of genetic conditions limiting hormone production in the adrenal glands.
ANSWER CHOICE D: Chromosome 12
Explanation: Chromosome 12 is the origin of several gene anomalies, including:
Pallister-Killian Mosaic Syndrome: Characterized by developmental delay, intellectual disability, and distinctive facial features.
PDGFRB-associated Chronic Eosinophilic Leukemia: A type of blood cell cancer involving chromosome 12 translocations.
Trisomy 12 in Chronic Lymphocytic Leukemia (CLL): An extra copy of chromosome 12 found in certain leukemia cases.
ANSWER CHOICE E: Chromosome 15
Explanation: Chromosome 15 is the origin of several gene anomalies, including:
Prader-Willi Syndrome: A genetic disorder characterized by obesity, intellectual disability, and short stature.
Angelman Syndrome: A genetic disorder causing developmental disabilities and nerve-related symptoms.
Chromosome 15q Duplication Syndrome: This syndrome involves duplications of the q arm of chromosome 15, which can lead to developmental delays and other symptoms.
FINAL VERDICT…
Von Willebrand disease is caused by mutations in the von Willebrand factor gene, which is located on chromosome 12. This condition leads to impaired platelet function and coagulation, resulting in the bleeding symptoms observed in the patient. The family history of mucocutaneous bleeding further supports this diagnosis.
CORRECT ANSWER: D) Chromosome 12
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Thanks for checking out Q61!
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