Molecular Pathology Practice Questions

Q: What is the primary molecular mechanism by which UV light induces carcinogenesis?

Thymine dimers. ***Thymine dimers*** - UV radiation, particularly **UVB**, causes structural damage to **DNA** by inducing the formation of **pyrimidine dimers** (specifically cyclobutane pyrimidine dimers involving thymine residues) between adjacent bases. - If these lesions are not effectively repaired by the **nucleotide excision repair (NER)** pathway, they lead to **mutations** (commonly C to T transitions) in critical genes like **TP53** during DNA replication, driving carcinogenesis. *Inhibition of TP53* - While UV damage often leads to mutations in the **TP53 gene**, this is a downstream consequence of DNA damage, not the primary molecular mechanism of UV-induced injury itself. - **TP53** is typically inactivated via **mutations** caused by failed repair of DNA photoproducts, rather than direct inhibition of the protein by UV light. *Activation of NF-kappa beta signaling pathway* - The **NF-kappaB pathway** is primarily involved in **inflammatory and immune responses** rather than being the direct mechanism of DNA damage-induced carcinogenesis. - While UV exposure does activate inflammatory pathways, this is a secondary response to tissue stress and not the foundational cause of **mutagenesis** and cancer initiation. *Upregulation of cyclin proteins* - Uncontrolled cell cycle progression due to **cyclin** dysregulation is a hallmark of cancer, but it is a result of accumulated **genetic mutations**. - This represents a cellular outcome of cancer development rather than the direct photochemical event initiated by UV radiation interacting with genomic DNA.

Q: A pathologist receives a formalin-fixed paraffin-embedded (FFPE) tissue section. Which technique is most appropriate to identify and localize specific proteins within this section in situ?

Immunohistochemistry (IHC). ***Immunohistochemistry (IHC)*** - This technique utilizes **specific antibodies** to detect and visualize target proteins directly within tissue sections, maintaining the **tissue architecture**. - It is the gold standard for **in situ protein localization** in formalin-fixed paraffin-embedded (FFPE) tissue, allowing pathologists to correlate protein expression with specific histological features. *Fluorescence in situ hybridisation (FISH)* - This molecular technique is specifically designed to detect **DNA or RNA sequences** rather than proteins within a cell. - It relies on **fluorescent probes** that bind to specific chromosomal or genetic targets, not the localization of proteins. *Flow cytometry* - While it can analyze protein expression, this technique requires the tissue to be dissociated into a **single-cell suspension**. - Because it destroys the **tissue architecture** and spatial relationships between cells, it is not used to localize proteins within an intact tissue section. *Western blot* - This technique is used to measure the **size and quantity** of a specific protein within a sample. - It requires total protein extraction from the sample, which destroys the **morphology and spatial distribution** of proteins, making it unsuitable for in situ localization.

Q: Which of the following conditions is not associated with an increased risk of malignancy?

Turner syndrome. **Explanation:** The question evaluates the association between chromosomal aneuploidies and the risk of malignancy. While many genetic syndromes predispose individuals to cancer due to genomic instability or hormonal imbalances, **Turner Syndrome (45, XO)** is generally **not** associated with an overall increased risk of malignancy compared to the general population. In fact, the risk of breast cancer is significantly lower in Turner patients due to ovarian dysgenesis and low estrogen levels. The only specific risk is a **gonadoblastoma**, which occurs only if there is cryptic Y-chromosome mosaicism (45,X/46,XY). **Analysis of Options:** * **Down’s Syndrome (Trisomy 21):** Strongly associated with a 10–20 fold increased risk of **Acute Leukemia** (AMKL/M7 in children <3 years and ALL in older children). * **Noonan Syndrome:** Often called "Pseudo-Turner," this autosomal dominant condition is associated with an increased risk of **Juvenile Myelomonocytic Leukemia (JMML)** and certain solid tumors like neuroblastoma. * **Klinefelter Syndrome (47, XXY):** These patients have a significantly higher risk of **Breast Cancer** (20–50 times higher than normal males) and **Extragonadal Germ Cell Tumors** (specifically mediastinal teratomas). **NEET-PG High-Yield Pearls:** 1. **Turner Syndrome:** Most common cause of primary amenorrhea; characterized by "streak ovaries," webbed neck, and coarctation of the aorta. 2. **Klinefelter Syndrome:** Most common cause of male hypogonadism and infertility; associated with taurodontism. 3. **Cancer Association:** Always remember the "Down-Leukemia" and "Klinefelter-Breast Cancer" links, as these are frequent examiners' favorites.

Q: Which of the following conditions is NOT inherited in an autosomal recessive pattern?

Marfan's syndrome. **Explanation:** The correct answer is **Marfan’s syndrome** because it follows an **Autosomal Dominant (AD)** inheritance pattern. It is caused by a mutation in the **FBN1 gene** on chromosome 15, which encodes **Fibrillin-1**, a critical glycoprotein for the structural integrity of the extracellular matrix. Since it is dominant, a single mutated allele from one parent is sufficient to cause the disease. **Analysis of Options:** * **Sickle cell anemia (A):** This is a classic **Autosomal Recessive (AR)** disorder caused by a point mutation in the HBB gene (Glu6Val). Clinical manifestation occurs only in the homozygous state (HbSS). * **Phenylketonuria (B):** An **AR** metabolic disorder involving a deficiency of the enzyme phenylalanine hydroxylase. It requires two defective alleles for the phenotype to appear. * **Wilson’s disease (D):** An **AR** disorder of copper metabolism caused by mutations in the **ATP7B gene** on chromosome 13. **NEET-PG High-Yield Pearls:** 1. **Marfan’s Syndrome:** Look for "Tall stature, Ectopia lentis (upward dislocation), and Aortic root dilatation." It exhibits **pleiotropy** (one gene affecting multiple systems). 2. **Mnemonic for AR diseases:** "Many Metabolic" diseases are AR (e.g., Glycogen storage diseases, Galactosemia, Cystic Fibrosis, and most enzyme deficiencies). 3. **Mnemonic for AD diseases:** "Structural" proteins are often AD (e.g., Marfan’s, Achondroplasia, Hereditary Spherocytosis, Osteogenesis Imperfecta) [1]. 4. **Exceptions:** Most enzyme deficiencies are AR, but **Hunter Syndrome** and **G6PD deficiency** are X-linked Recessive.

Q: Which of the following is true for Klinefelter's syndrome?

Tall stature. **Explanation:** **Klinefelter Syndrome (47, XXY)** is the most common cause of male hypogonadism and occurs due to meiotic non-disjunction of sex chromosomes. 1. **Why "Tall Stature" is correct:** Patients with Klinefelter syndrome possess an extra X chromosome. The **SHOX gene** (Short Stature Homeobox gene), located on the distal short arms of the X and Y chromosomes, remains active. An extra copy of the SHOX gene leads to increased skeletal growth, resulting in **tall stature** and elongated lower limbs (eunuchoid body habitus) [1]. 2. **Why the other options are incorrect:** * **Option A (45, XO):** This is the karyotype for **Turner Syndrome**, which presents in females with short stature and streak ovaries [1]. * **Option C (Normal IQ):** While many patients have near-normal intelligence, there is a statistically significant association with **mild intellectual disability** or learning disabilities (specifically verbal lag). The degree of impairment often increases with the number of extra X chromosomes (e.g., 48, XXXY). * **Option D (Normal testes):** This is incorrect. The hallmark of Klinefelter is **testicular dysgenesis**. Patients present with small, firm testes, hyalinization of seminiferous tubules, and Leydig cell hyperplasia. **High-Yield Clinical Pearls for NEET-PG:** * **Karyotype:** Most commonly 47, XXY. * **Hormonal Profile:** Low Testosterone, **High FSH and LH** (Hypergonadotropic hypogonadism), and increased Estradiol. * **Clinical Features:** Gynecomastia (increased risk of male breast cancer), infertility (azoospermia), and reduced secondary male sexual characteristics. * **Barr Body:** Positive (due to the extra X chromosome). **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Genetic Disorders, pp. 173-174.

Q: Lisch nodules and a pancreatic somatostatinoma are seen in which condition?

Neurofibromatosis. **Explanation:** The correct answer is **Neurofibromatosis Type 1 (NF1)**. **1. Why Neurofibromatosis is correct:** Neurofibromatosis Type 1 (von Recklinghausen disease) is an autosomal dominant neurocutaneous syndrome caused by a mutation in the *NF1* gene on chromosome 17. * **Lisch Nodules:** These are melanocytic hamartomas of the iris, appearing as well-defined, dome-shaped brown papules. They are a hallmark diagnostic feature of NF1. * **Somatostatinoma:** While rare, there is a specific and high-yield association between NF1 and **duodenal/pancreatic somatostatinomas**. These tumors often contain psammoma bodies and are part of the spectrum of neuroendocrine tumors associated with the NF1 mutation [1]. **2. Why other options are incorrect:** * **MEN 2A:** Characterized by Medullary Thyroid Carcinoma, Pheochromocytoma, and Parathyroid Hyperplasia. It is not associated with Lisch nodules or somatostatinomas. * **Turcot Syndrome:** A variant of FAP or HNPCC involving colonic polyposis associated with CNS tumors (Medulloblastoma or Glioblastoma). * **Familial Adenomatous Polyposis (FAP):** Characterized by thousands of colonic adenomas and extracolonic manifestations like osteomas and desmoid tumors (Gardner syndrome), but not Lisch nodules. **3. Clinical Pearls for NEET-PG:** * **NF1 Diagnostic Criteria (NIH):** Remember the mnemonic **CAFE SPOT** (Café-au-lait spots, Axillary/inguinal freckling, Fibromas [Neurofibromas], Eye [Lisch nodules], Skeletal [Sphenoid dysplasia], Positive family history, Optic Tumor [Glioma]). * **Somatostatinoma Triad:** Diabetes mellitus, Steatorrhea, and Cholelithiasis (due to inhibition of insulin, pancreatic enzymes, and CCK) [1]. * **NF1 + Hypertension:** Always rule out **Pheochromocytoma** or **Renal Artery Stenosis** (due to fibromuscular dysplasia).

Q: Which genetic abnormality is depicted by the following FISH technique? *Probe legend:* Red probe = BCR (chromosome 22); Green probe = ABL (chromosome 9). Expected normal signal pattern: 2 red + 2 green (separate signals). The image shows an apparent 1-red/2-green interphase pattern, suggesting loss of one red (BCR) probe signal.

Deletion. ***Deletion*** - **FISH** can detect **loss of a chromosomal locus** when one probe signal is absent or reduced compared to the expected copy number. - The image shows an **1-red/2-green pattern**, indicating loss of one **BCR (chromosome 22)** signal, consistent with a **deletion** of that locus. - Expected normal pattern is **2 red + 2 green**; loss of one red signal indicates deletion of the BCR region on one copy of chromosome 22. *Translocation* - Would be detected by a **dual-fusion** assay showing **yellow fusion signals** where red and green probes colocalize (e.g., BCR-ABL in CML). - The image does **not** show yellow fusion signals; the red and green signals remain predominantly **separate**, ruling out a translocation pattern. *Duplication* - Appears as **increased signal intensity** or **additional copies** of the fluorescent probe in the same chromosomal location. - Shows **amplified signals** rather than the loss of signal seen here. *Ligation* - Not a **chromosomal abnormality** but rather a **molecular biology technique** involving joining DNA fragments. - Has no relevance to **cytogenetic analysis** or FISH-detectable chromosomal rearrangements.

Question 1

What is the primary molecular mechanism by which UV light induces carcinogenesis?

Accepted Answer

Thymine dimers

Answer

Inhibition of TP53

Answer

Activation of NF-kappa beta signaling pathway

Answer

Upregulation of cyclin proteins

Question 2

A pathologist receives a formalin-fixed paraffin-embedded (FFPE) tissue section. Which
technique is most appropriate to identify and localize specific proteins within this section in situ?

Accepted Answer

Immunohistochemistry (IHC)

Answer

Flow cytometry

Answer

Western blot

Answer

Fluorescence in situ hybridisation (FISH)

Question 3

Which of the following conditions is not associated with an increased risk of malignancy?

Accepted Answer

Turner syndrome

Answer

Down's syndrome

Answer

Noonan syndrome

Answer

Klinefelter syndrome

Question 4

Which of the following is an autosomal dominant metabolic disorder?

Accepted Answer

Familial hypercholesterolemia

Answer

Cystic fibrosis

Answer

Phenylketonuria

Answer

Alpha-1 anti-trypsin deficiency

Question 5

A female patient presents with a 2 x 2 cm firm mass in the upper outer quadrant of the breast. She has a family history of ovarian carcinoma. Which investigation needs to be done to assess for a specific gene mutation?

Accepted Answer

BRCA-2

Answer

p53

Answer

Her 2/Neu gene

Answer

C-myc gene

Question 6

Which of the following conditions is NOT inherited in an autosomal recessive pattern?

Accepted Answer

Marfan's syndrome

Answer

Sickle cell anemia

Answer

Phenylketonuria

Answer

Wilson's disease

Question 7

Which of the following is true for Klinefelter's syndrome?

Accepted Answer

Tall stature

Answer

45, XO

Answer

Normal Intelligence Quotient

Answer

Normal testes and genitalia

Question 8

Lisch nodules and a pancreatic somatostatinoma are seen in which condition?

Accepted Answer

Neurofibromatosis

Answer

Multiple endocrine neoplasia 2A

Answer

Turcot syndrome

Answer

Familial adenomatous polyposis

Question 9

Which genetic abnormality is depicted by the following FISH technique?

*Probe legend:* Red probe = BCR (chromosome 22); Green probe = ABL (chromosome 9). Expected normal signal pattern: 2 red + 2 green (separate signals). The image shows an apparent 1-red/2-green interphase pattern, suggesting loss of one red (BCR) probe signal.

Accepted Answer

Deletion

Answer

Ligation

Answer

Translocation

Answer

Duplication

Question 10

Which of the following chromosomal abnormalities is most likely to cause mental retardation?

Accepted Answer

Trisomy 21

Answer

Klinefelter's syndrome

Answer

Fusion of chromosomes 21 and 15

Answer

Turner's syndrome

Molecular Pathology — MCQs

Molecular Pathology — MCQs

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