Molecular Pathology — MCQs

Molecular Pathology Indian Medical PG Practice Questions and MCQs

Question 61: Which of the following is a pro-apoptotic factor?

A. Bax (Correct Answer)
B. Bcl-2
C. Bcl-xL
D. Mcl-1

Explanation: **Explanation:** Apoptosis (programmed cell death) is tightly regulated by the **Bcl-2 family of proteins**, which act as a molecular switch for the intrinsic (mitochondrial) pathway [2]. These proteins are categorized into two functional groups: pro-apoptotic and anti-apoptotic. **Why Bax is Correct:** **Bax** (along with **Bak**) is a **pro-apoptotic effector** protein [1]. When activated by cellular stress or DNA damage, Bax and Bak oligomerize and insert into the outer mitochondrial membrane. This creates pores, leading to **Mitochondrial Outer Membrane Permeabilization (MOMP)**. This allows the release of **Cytochrome c** into the cytosol, which activates the caspase cascade, ultimately leading to cell death. **Why the Other Options are Incorrect:** * **Bcl-2, Bcl-xL, and Mcl-1 (Options B, C, and D):** These are all **anti-apoptotic (pro-survival)** proteins [1]. They reside in the mitochondrial membranes and cytosol, where they bind to and inhibit pro-apoptotic sensors and effectors. Their primary role is to prevent the leakage of Cytochrome c, thereby keeping the cell alive. **High-Yield Clinical Pearls for NEET-PG:** * **The Ratio Matters:** The balance between pro-apoptotic (Bax/Bak) and anti-apoptotic (Bcl-2/Bcl-xL) factors determines the cell's fate [2]. * **BH3-only proteins:** Proteins like **Bad, Bim, and Bid** are "sensors" that neutralize anti-apoptotic proteins, allowing Bax/Bak to function. * **Follicular Lymphoma:** Characterized by the **t(14;18)** translocation, which leads to the overexpression of **Bcl-2**, preventing apoptosis and allowing neoplastic B-cells to survive [3]. * **Mnemonic:** "Bax" and "Bak" make the mitochondrial membrane "leak." **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Neoplasia, p. 310. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Cellular Responses to Stress and Toxic Insults: Adaptation, Injury, and Death, pp. 64-65. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Neoplasia, pp. 310-311.

Question 62: In Vitamin-A deficiency, cancerous lesions occur due to which cellular adaptation?

A. Metaplasia (Correct Answer)
B. Dysplasia
C. Aplasia
D. Hyperplasia

Explanation: **Explanation:** **Why Metaplasia is Correct:** Vitamin A (Retinoic acid) is essential for the normal differentiation of epithelial tissues. It acts as a transcription factor by binding to nuclear receptors, ensuring that specialized epithelia (like the mucus-secreting columnar epithelium of the respiratory tract) maintain their specific characteristics. In **Vitamin A deficiency**, this regulatory signal is lost, leading to **Squamous Metaplasia**. The delicate columnar epithelium is replaced by a rugged, stratified squamous epithelium. While this new epithelium is more resistant to physical stress, it loses vital functions (like mucus secretion) [1]. If the underlying stimulus (deficiency) persists, this metaplastic epithelium can undergo genetic mutations, progressing to **dysplasia** [2] and eventually **squamous cell carcinoma** [1]. **Why Other Options are Incorrect:** * **Dysplasia:** This refers to disordered growth and loss of cellular architectural uniformity [2]. While dysplasia is a precursor to cancer, it is the *consequence* of persistent metaplasia in this context, not the primary cellular adaptation caused directly by the deficiency. * **Aplasia:** This refers to the failure of an organ or tissue to develop or function. It is a developmental or regenerative failure, not a transformation of cell types. * **Hyperplasia:** This is an increase in the number of cells in an organ. While it can coexist with other changes [2], it does not describe the change in cell *type* (differentiation) characteristic of Vitamin A deficiency. **High-Yield Clinical Pearls for NEET-PG:** * **Bitot’s Spots:** Keratin debris on the conjunctiva due to squamous metaplasia. * **Keratomalacia:** Softening and ulceration of the cornea. * **Xerophthalmia:** Pathological dryness of the conjunctiva and cornea. * **Therapeutic Use:** All-trans retinoic acid (ATRA) is used in Acute Promyelocytic Leukemia (APL - M3) to induce the differentiation of leukemic blasts. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Cellular Responses to Stress and Toxic Insults: Adaptation, Injury, and Death, p. 49. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Lung, p. 723.

Question 63: Steroid-resistant nephrotic syndrome is associated with mutations in which gene?

A. NPHS2 (Correct Answer)
B. HOX11
C. PAX
D. ACE

Explanation: **Explanation:** The correct answer is **A. NPHS2**. **1. Why NPHS2 is correct:** Steroid-resistant nephrotic syndrome (SRNS) is frequently caused by genetic mutations affecting the structural integrity of the glomerular filtration barrier [1]. The **NPHS2 gene** encodes **Podocin**, a critical integral membrane protein localized to the slit diaphragm of podocytes [1]. Mutations in NPHS2 lead to autosomal recessive SRNS, typically manifesting as Focal Segmental Glomerulosclerosis (FSGS). Unlike minimal change disease, these genetic forms do not respond to corticosteroid therapy because the defect is structural rather than immunological [1]. **2. Why the other options are incorrect:** * **HOX11 (TLX1):** This is a homeobox gene primarily associated with T-cell acute lymphoblastic leukemia (T-ALL) and spleen development, not renal filtration. * **PAX:** The PAX gene family (e.g., PAX2, PAX8) is crucial for kidney development (nephrogenesis). Mutations in PAX2 are associated with Renal-Coloboma Syndrome, characterized by optic nerve coloboma and renal hypoplasia, but not specifically SRNS. * **ACE:** The Angiotensin-Converting Enzyme gene is studied for its role in hypertension and the progression of chronic kidney disease, but it is not the primary causative mutation for steroid-resistant nephrotic syndrome. **High-Yield Clinical Pearls for NEET-PG:** * **NPHS1:** Encodes **Nephrin**. Mutations cause Finnish-type congenital nephrotic syndrome (autosomal recessive). * **NPHS2:** Encodes **Podocin**. Associated with childhood-onset SRNS and FSGS [1]. * **ACTN4:** Encodes ̡-actinin-4; mutations cause an autosomal dominant form of FSGS [1]. * **WT1:** Mutations can lead to Denys-Drash syndrome (nephropathy, Wilms tumor, and intersex disorders). **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Kidney, pp. 921-928.

Question 64: Which of the following chromosomal abnormalities will exhibit two Barr bodies?

A. 47, XXX (Correct Answer)
B. 47, XXY
C. 45, X0
D. 46, XY

Explanation: **Explanation:** The number of Barr bodies in a cell is determined by the **Lyon Hypothesis**, which states that in individuals with more than one X chromosome, all except one X chromosome are inactivated to ensure dosage compensation. The formula to calculate the number of Barr bodies is: **Number of Barr bodies = Total number of X chromosomes – 1** **1. Why Option A (47, XXX) is correct:** In Triple X syndrome, there are three X chromosomes [1]. Applying the formula (3 - 1 = 2), these individuals exhibit **two Barr bodies** in their somatic cell nuclei (e.g., buccal smear). **2. Analysis of Incorrect Options:** * **47, XXY (Klinefelter Syndrome):** Despite being phenotypically male, these individuals have two X chromosomes [1]. Therefore, they exhibit **one Barr body** (2 - 1 = 1). * **45, X0 (Turner Syndrome):** These individuals have only one X chromosome. Since 1 - 1 = 0, they exhibit **no Barr bodies**. * **46, XY (Normal Male):** Normal males have only one X chromosome and thus show **no Barr bodies**. **High-Yield Clinical Pearls for NEET-PG:** * **Barr Body Composition:** It is composed of highly condensed **facultative heterochromatin**. * **XIST Gene:** Located on the X-inactivation center (Xic) at **Xq13**, the *XIST* non-coding RNA is essential for the initiation and spread of X-inactivation. * **Drumstick Appearance:** In peripheral blood smears, the Barr body appears as a "drumstick" appendage on the nucleus of **polymorphonuclear neutrophils (PMNs)**. * **Timing:** X-inactivation occurs early in embryonic life (blastocyst stage, approximately day 15-16). **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. (Basic Pathology) introduces the student to key general principles of pathology, both as a medical science and as a clinical activity with a vital role in patient care. Part 2 (Disease Mechanisms) provides fundamental knowledge about the cellular and molecular processes involved in diseases, providing the rationale for their treatment. Part 3 (Systematic Pathology) deals in detail with specific diseases, with emphasis on the clinically important aspects., pp. 92-93.

Question 65: A 56-year-old chronic smoker presents with a mass in the bronchus that was resected. What is the most useful immunohistochemical marker for making a definitive diagnosis?

A. Cytokeratin (Correct Answer)
B. Vimentin
C. Epithelial membrane antigen
D. Leukocyte common antigen

Explanation: ### Explanation **1. Why Cytokeratin (CK) is the Correct Answer:** The clinical presentation (56-year-old chronic smoker with a bronchial mass) is highly suggestive of **Bronchogenic Carcinoma** (most commonly Squamous Cell Carcinoma or Small Cell Carcinoma). These are **epithelial tumors**. Cytokeratins are intermediate filaments found specifically in the intracytoplasmic cytoskeleton of epithelial cells. IHC staining for CK is the gold standard for confirming the epithelial origin of a tumor, thereby definitively diagnosing it as a **Carcinoma** [1]. **2. Analysis of Incorrect Options:** * **Vimentin:** This is the intermediate filament marker for **mesenchymal cells**. It is used to diagnose sarcomas (e.g., fibrosarcoma, osteosarcoma) [1]. While some carcinomas can show focal vimentin expression (epithelial-mesenchymal transition), it is not the primary diagnostic marker for a bronchial mass. * **Epithelial Membrane Antigen (EMA):** While EMA is expressed by many carcinomas, it is less specific than Cytokeratin. It is also expressed in some plasma cell tumors and certain sarcomas (like synovial sarcoma), making it less reliable for a definitive primary diagnosis of a bronchial mass. * **Leukocyte Common Antigen (LCA/CD45):** This is the definitive marker for **hematolymphoid malignancies** (Lymphomas/Leukemias). It would be used if the differential diagnosis included a primary pulmonary lymphoma, which is much rarer than carcinoma in a chronic smoker [1]. **3. NEET-PG High-Yield Clinical Pearls:** * **CK7+/CK20-:** Pattern typically seen in Primary Lung Adenocarcinoma. * **p40 and p63:** Highly specific markers for **Squamous Cell Carcinoma** of the lung. * **TTF-1 (Thyroid Transcription Factor-1):** Positive in Lung Adenocarcinoma and Small Cell Carcinoma (also positive in Thyroid tumors). * **Synaptophysin/Chromogranin:** Markers used for **Neuroendocrine tumors** (Small Cell and Carcinoid). * **Rule of Thumb:** Carcinoma = Cytokeratin; Sarcoma = Vimentin; Lymphoma = LCA; Melanoma = S100/HMB-45. **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. (Basic Pathology) introduces the student to key general principles of pathology, both as a medical science and as a clinical activity with a vital role in patient care. Part 2 (Disease Mechanisms) provides fundamental knowledge about the cellular and molecular processes involved in diseases, providing the rationale for their treatment. Part 3 (Systematic Pathology) deals in detail with specific diseases, with emphasis on the clinically important aspects., pp. 208-209.

Question 66: The gene for Wilms tumor is located on which chromosome?

A. Chromosome 11 (Correct Answer)
B. Chromosome 1
C. Chromosome 10
D. Chromosome 12

Explanation: **Explanation:** **1. Why Chromosome 11 is Correct:** Wilms tumor (Nephroblastoma) is the most common primary renal tumor of childhood. Its pathogenesis is strongly linked to the **WT1 (Wilms Tumor 1) gene**, which is located on **Chromosome 11p13** [1]. This gene is essential for normal renal and gonadal development. Mutations or deletions in this region are associated with sporadic Wilms tumor and syndromic forms like **WAGR syndrome** (Wilms tumor, Aniridia, Genitourinary anomalies, and mental Retardation) [1]. Additionally, the **WT2 gene** locus is located on **Chromosome 11p15.5**, associated with **Beckwith-Wiedemann Syndrome**. **2. Analysis of Incorrect Options:** * **Chromosome 1:** While many cancers have secondary changes here, it is not the primary locus for Wilms tumor. However, 1p deletions are sometimes seen as a poor prognostic marker in Wilms. * **Chromosome 10:** This is the location of the **PTEN gene** (Cowden syndrome) and the **RET proto-oncogene** (MEN 2A/2B and Medullary Thyroid Carcinoma). * **Chromosome 12:** Associated with genes like **KRAS** and certain sarcomas (e.g., Clear cell sarcoma of the kidney), but not the classic Wilms tumor gene. **3. High-Yield Clinical Pearls for NEET-PG:** * **Histology:** Characterized by a **triphasic pattern** (Blastema, Stroma, and Epithelium). * **Denys-Drash Syndrome:** Associated with WT1 mutations, characterized by gonadal dysgenesis and early-onset nephropathy. * **Beckwith-Wiedemann Syndrome (BWS):** Linked to the WT2 locus (11p15.5); features include macroglossia, organomegaly, and hemihypertrophy. * **Prognosis:** The presence of **anaplasia** (TP53 mutation) is the most important histological predictor of poor prognosis. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of Infancy and Childhood, pp. 487-488.

Question 67: All of the following are true about dyskeratosis congenita, EXCEPT:

A. Cutaneous depigmentation (Correct Answer)
B. Leukoplakia
C. Nail dystrophy
D. Shortened telomere length in leukocytes

Explanation: ### Explanation **Dyskeratosis Congenita (DKC)** is a rare inherited bone marrow failure syndrome characterized by the classic **clinical triad**: 1. **Nail dystrophy** (ridged, split, or absent nails) 2. **Oral leukoplakia** (white patches on the tongue/mucosa) 3. **Reticular skin hyperpigmentation** (typically in a "lace-like" pattern on the neck and chest) **Why Option A is the Correct Answer:** The cutaneous manifestation of DKC is **hyperpigmentation**, not depigmentation. The skin changes usually appear in the first decade of life and are characterized by a dusky, reticular (net-like) pattern of increased melanin deposition. **Analysis of Other Options:** * **Option B (Leukoplakia):** This is a hallmark of the classic triad. It carries a high risk of malignant transformation into squamous cell carcinoma. * **Option C (Nail Dystrophy):** This is often the earliest sign of the triad, appearing in early childhood. * **Option D (Shortened telomere length):** DKC is fundamentally a **"telomeropathy."** It is caused by mutations in genes responsible for telomere maintenance (e.g., *DKC1, TERC, TERT*). Measuring telomere length in peripheral blood leukocytes via Flow-FISH is the gold-standard diagnostic test. **High-Yield Clinical Pearls for NEET-PG:** * **Inheritance:** Most commonly X-linked recessive (*DKC1* gene encoding **dyskerin**), but autosomal dominant and recessive forms exist. * **Primary Cause of Death:** Bone marrow failure (aplastic anemia) occurs in ~80% of patients. * **Cancer Risk:** Significant predisposition to Head and Neck Squamous Cell Carcinoma (HNSCC) and Myelodysplastic Syndrome (MDS). * **Hoyeraal-Hreidarsson Syndrome:** A severe variant of DKC characterized by cerebellar hypoplasia and immunodeficiency.

Question 68: Cat eye syndrome is a chromosomal abnormality characterized by which of the following?

A. Trisomy 18
B. Trisomy 13
C. Trisomy 21
D. Trisomy 22 (Correct Answer)

Explanation: **Explanation:** **Cat Eye Syndrome (Schmid-Fraccaro Syndrome)** is a rare chromosomal disorder typically caused by a partial tetrasomy of the short arm (p) and a small section of the long arm (q) of **chromosome 22**. Specifically, it involves an extra marker chromosome (inv dup 22q11). While technically a partial tetrasomy, in the context of standard medical examinations like NEET-PG, it is classically associated with **Trisomy 22** (specifically partial trisomy/tetrasomy 22). The syndrome derives its name from the characteristic vertical coloboma of the iris, which resembles the pupil of a cat. **Analysis of Options:** * **Trisomy 18 (Edwards Syndrome):** Characterized by micrognathia, low-set ears, clenched fists with overlapping fingers, and rocker-bottom feet [1], [2]. * **Trisomy 13 (Patau Syndrome):** Characterized by midline defects such as holoprosencephaly, cleft lip/palate, polydactyly, and microphthalmia [1]. * **Trisomy 21 (Down Syndrome):** The most common autosomal trisomy, presenting with epicanthal folds, Simian crease, intellectual disability, and cardiac defects (endocardial cushion defects) [1], [2]. **High-Yield Clinical Pearls for NEET-PG:** * **Clinical Triad:** The classic presentation includes **Iris Coloboma**, **Anal Atresia** (with fistula), and **Preauricular pits/tags**. * **Genetics:** It is usually a de novo mutation involving the 22q11 region, but it is distinct from DiGeorge Syndrome (which is a microdeletion of 22q11.2) [1]. * **Other features:** Congenital heart defects (often TAPVC) and renal abnormalities. * **Mnemonic:** Remember the **"3 As"** of Cat Eye Syndrome: **A**nal atresia, **A**uricular tags, and **A**bnormal iris (Coloboma). **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Genetic Disorders, pp. 170-173. [2] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. (Basic Pathology) introduces the student to key general principles of pathology, both as a medical science and as a clinical activity with a vital role in patient care. Part 2 (Disease Mechanisms) provides fundamental knowledge about the cellular and molecular processes involved in diseases, providing the rationale for their treatment. Part 3 (Systematic Pathology) deals in detail with specific diseases, with emphasis on the clinically important aspects., pp. 92-93.

Question 69: Angelman syndrome is caused by:

A. Maternal imprinting (Correct Answer)
B. Paternal imprinting
C. Both of the above
D. None of the above

Explanation: **Explanation:** Angelman syndrome is a classic example of **Genomic Imprinting**, an epigenetic process where certain genes are expressed in a parent-of-origin-specific manner [1]. **1. Why Maternal Imprinting is Correct:** In normal individuals, the **UBE3A gene** on chromosome 15 (15q11-q13) is active only on the maternal chromosome, while the paternal copy is silenced (imprinted). Angelman syndrome occurs when the **maternal** contribution is lost—either through a deletion of the maternal 15q11-q13 region (70% of cases), paternal uniparental disomy (two copies from the father), or imprinting defects [1]. Because the paternal gene is already silenced, the loss of the functional maternal gene leads to a total lack of UBE3A expression in the brain. **2. Why Other Options are Incorrect:** * **Paternal Imprinting:** This refers to the silencing of the paternal allele. If the **paternal** contribution is lost (and the maternal copy is silenced), it results in **Prader-Willi Syndrome**, not Angelman [1]. * **Both/None:** These are incorrect as the syndromes are distinct clinical entities based on which parental allele is defective [1]. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic:** **M**aternal = **A**ngelman (**M**appy **A**ngel); **P**aternal = **P**rader-Willi (**P**opular **P**rader). * **Angelman Presentation:** "Happy Puppet" syndrome—characterized by inappropriate laughter, seizures, ataxia, and severe intellectual disability [1]. * **Prader-Willi Presentation:** Hyperphagia (obesity), hypogonadism, and hypotonia [1]. * **Diagnosis:** Fluorescence in situ hybridization (FISH) or methylation-specific PCR [1]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Genetic Disorders, pp. 181-182.

Question 70: Which of the following tests is not used for the detection of specific aneuploidy?

A. FISH
B. None
C. QF-PCR
D. Microarray (Correct Answer)

Explanation: **Explanation:** The core of this question lies in the distinction between **targeted** detection of specific chromosomes and **genome-wide** screening. **1. Why Microarray is the correct answer:** Chromosomal Microarray (CMA) is a high-resolution, genome-wide screening tool. While it can detect aneuploidy, it is **not specific** to a pre-selected chromosome [1]. Instead, it scans the entire genome to identify copy number variants (CNVs), microdeletions, and microduplications. Unlike FISH or QF-PCR, you do not need to "suspect" a specific trisomy beforehand to use a microarray; it provides a comprehensive map of gains and losses across all chromosomes [1]. **2. Why the other options are incorrect:** * **FISH (Fluorescence In Situ Hybridization):** This is a targeted technique. It uses fluorescent probes specific to a particular chromosome (e.g., probes for 13, 18, 21, X, and Y) [1]. It is the gold standard for rapid detection of **specific** suspected aneuploidies in prenatal diagnosis. * **QF-PCR (Quantitative Fluorescence Polymerase Chain Reaction):** This is a highly specific molecular method. It uses chromosome-specific polymorphic markers (STRs) to quantify the amount of DNA. It is specifically designed to detect common aneuploidies (Trisomy 13, 18, 21) rapidly. **Clinical Pearls for NEET-PG:** * **Karyotyping:** Detects balanced translocations (Microarray cannot detect balanced rearrangements because there is no change in the "amount" of DNA). Karyotyping allows chromosomes to be counted and grouped to reveal disorders like trisomy [2]. * **Microarray:** The first-line investigation for children with multiple congenital anomalies, developmental delay, or autism. * **Resolution:** Microarray (10-100 kb) > Karyotyping (5-10 Mb). * **QF-PCR:** Preferred for rapid prenatal diagnosis due to its high throughput and lower cost compared to FISH. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Genetic Disorders, pp. 186-187. [2] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. (Basic Pathology) introduces the student to key general principles of pathology, both as a medical science and as a clinical activity with a vital role in patient care. Part 2 (Disease Mechanisms) provides fundamental knowledge about the cellular and molecular processes involved in diseases, providing the rationale for their treatment. Part 3 (Systematic Pathology) deals in detail with specific diseases, with emphasis on the clinically important aspects., pp. 54-55.

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