General Pathology — MCQs

General Pathology Indian Medical PG Practice Questions and MCQs

Question 1131: Which gene is mutated in familial gastric cancer?

A. APC
B. CDKN2A
C. E-cadherin (Correct Answer)
D. PTEN

Explanation: **Explanation:** The correct answer is **E-cadherin (CDH1)**. Hereditary Diffuse Gastric Cancer (HDGC) is an autosomal dominant syndrome most commonly caused by germline mutations in the **CDH1 gene**, which encodes the cell adhesion protein E-cadherin [1]. **Why E-cadherin is correct:** E-cadherin is essential for maintaining epithelial cell-to-cell adhesion. A mutation leads to a loss of "contact inhibition," allowing cells to become discohesive [1]. This results in the characteristic **"Signet Ring Cell"** morphology, where cells infiltrate the gastric wall individually rather than forming a solid mass (Linitis Plastica). **Analysis of Incorrect Options:** * **APC (Adenomatous Polyposis Coli):** Mutated in Familial Adenomatous Polyposis (FAP). While FAP increases the risk of intestinal-type gastric polyps, it is not the primary driver of familial diffuse gastric cancer. * **CDKN2A:** This gene encodes p16 and is primarily associated with **Familial Melanoma** [1] and Pancreatic Cancer [2]. * **PTEN:** Mutated in **Cowden Syndrome**. While it increases the risk of various hamartomas and cancers (Breast, Thyroid, Endometrial), it is not the classic cause of familial gastric cancer. **High-Yield NEET-PG Pearls:** 1. **Morphology:** CDH1 mutations are specifically linked to **Diffuse-type** gastric adenocarcinoma (not the intestinal type). 2. **Associated Risks:** Women with CDH1 mutations also have a significantly high risk of **Lobular Carcinoma of the Breast**. 3. **Prophylaxis:** Due to the high penetrance and difficulty in early endoscopic detection, prophylactic total gastrectomy is often recommended for carriers. 4. **Snail/Twist:** These transcription factors downregulate E-cadherin during the Epithelial-Mesenchymal Transition (EMT) in cancer metastasis [1]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Neoplasia, pp. 305-306. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Pancreas, pp. 898-899.

Question 1132: Pseudo-rosettes are characteristic findings in which of the following conditions?

A. Retinoblastoma (Correct Answer)
B. Ophthalmic nodosa
C. Phacolytic glaucoma
D. Trachoma

Explanation: **Explanation:** **Retinoblastoma** is the most common intraocular tumor of childhood, classically associated with the formation of rosettes [1], [2]. In pathology, a "rosette" refers to a circular arrangement of tumor cells. In Retinoblastoma, two types of rosettes are seen: 1. **Flexner-Wintersteiner Rosettes:** These are "true rosettes" characterized by a central lumen [1]. They are highly specific for Retinoblastoma. 2. **Homer Wright Rosettes:** These are **"pseudo-rosettes"** because they lack a true central lumen; instead, the cells surround a central tangle of neural fibrils (neuropil). While characteristic of Retinoblastoma, they are also seen in other primitive neuroectodermal tumors like Medulloblastoma and Neuroblastoma [2]. **Analysis of Incorrect Options:** * **Ophthalmic nodosa:** A granulomatous inflammatory reaction of the eye caused by irritation from caterpillar hairs. It shows granulomas, not rosettes. * **Phacolytic glaucoma:** An inflammatory glaucoma caused by the leakage of lens proteins through the capsule of a mature cataract. Histology shows macrophages laden with lens material. * **Trachoma:** Caused by *Chlamydia trachomatis* (Serotypes A, B, Ba, C). It is characterized by follicular conjunctivitis and "Halberstaedter-Prowazek" intracytoplasmic inclusion bodies, not rosettes. **NEET-PG High-Yield Pearls:** * **Flexner-Wintersteiner Rosettes:** Specific for Retinoblastoma and Pineoblastoma. * **Homer Wright Rosettes:** Seen in Retinoblastoma, Neuroblastoma, and Medulloblastoma. * **Flexner-Wintersteiner = True Lumen; Homer Wright = No Lumen (Fibrillar core).** * **Fleurettes:** These represent photoreceptor differentiation and are also a diagnostic feature of Retinoblastoma. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Eye, pp. 1341-1342. [2] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Manifestations Of Central And Peripheral Nervous System Disease, pp. 737-738.

Question 1133: Renal pathology in SLE includes all EXCEPT?

A. Focal glomerulonephritis
B. Diffuse glomerulonephritis
C. Membranous glomerulonephritis
D. Lipoid nephrosis (Correct Answer)

Explanation: **Explanation:** The renal involvement in Systemic Lupus Erythematosus (SLE) is categorized by the **ISN/RPS classification** into six distinct classes [2]. The correct answer is **Lipoid nephrosis** (also known as Minimal Change Disease), as it is not a recognized manifestation of Lupus Nephritis. **Why Lipoid Nephrosis is the correct answer:** Lipoid nephrosis is characterized by the effacement of podocyte foot processes without immune complex deposition. In contrast, Lupus Nephritis is a classic **Type III Hypersensitivity** reaction driven by the deposition of DNA-anti-DNA immune complexes within the glomeruli [1]. While SLE patients can rarely develop podocytopathy, "Lipoid Nephrosis" is a distinct clinical entity not included in the standard SLE renal pathology spectrum. **Analysis of Incorrect Options:** * **A. Focal glomerulonephritis (Class III):** Involves <50% of glomeruli; characterized by endocapillary proliferation and subendothelial deposits [2]. * **B. Diffuse glomerulonephritis (Class IV):** The most common and most severe form [3]. It involves >50% of glomeruli and often presents with "wire-loop" lesions [3]. * **C. Membranous glomerulonephritis (Class V):** Characterized by subepithelial deposits and diffuse thickening of the glomerular capillary wall, similar to idiopathic membranous nephropathy [4]. **High-Yield Clinical Pearls for NEET-PG:** * **Most common and most severe class:** Class IV (Diffuse Proliferative) [3]. * **Most common cause of death in SLE:** Renal failure [4]. * **Wire-loop lesions:** Represent extensive subendothelial deposits (highly characteristic of Class IV) [3]. * **Hematoxylin bodies (Gross bodies):** The only pathognomonic finding for SLE (though rarely seen). * **Full House Pattern:** Immunofluorescence showing IgG, IgA, IgM, C3, and C1q positivity [4]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, p. 226. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 230-232. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, p. 232. [4] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Diseases Of The Urinary And Male Genital Tracts, pp. 532-533.

Question 1134: Which of the following has a direct role in apoptosis?

A. Nitric oxide
B. Adenylcyclase
C. cAMP
D. Cytochrome C (Correct Answer)

Explanation: **Explanation:** **Cytochrome C** is a critical component of the **Intrinsic (Mitochondrial) Pathway** of apoptosis [2]. Under conditions of cellular stress or DNA damage, the pro-apoptotic proteins (BAX and BAK) create pores in the outer mitochondrial membrane [1]. This leads to the leakage of Cytochrome C from the intermembrane space into the cytosol. Once in the cytosol, Cytochrome C binds to **Apaf-1** (Apoptotic protease activating factor-1) to form a wheel-like hexamer called the **Apoptosome** [1]. This complex activates **Caspase-9**, triggering the executioner caspase cascade (Caspases 3, 6, and 7) that leads to cell death [1]. **Analysis of Incorrect Options:** * **Nitric Oxide (NO):** Primarily acts as a vasodilator and neurotransmitter. While it can modulate cell survival in high concentrations via oxidative stress, it is not a direct structural or signaling component of the core apoptotic machinery. * **Adenylcyclase & cAMP:** These are components of the G-protein coupled receptor (GPCR) signaling pathway. They function as second messengers for hormonal signaling and metabolic regulation, rather than direct mediators of the programmed cell death pathway. **NEET-PG High-Yield Pearls:** * **Guardian of the Genome:** p53 triggers apoptosis by upregulating BAX/BAK when DNA damage is irreparable [1]. * **Anti-apoptotic markers:** BCL-2 and BCL-XL (they stabilize the mitochondrial membrane) [2]. * **Executioner Caspases:** Caspase 3 is the most common executioner caspase [2]. * **Marker for Apoptosis:** Annexin V (binds to Phosphatidylserine flipped to the outer membrane leaflet). * **DNA Laddering:** A characteristic electrophoretic pattern in apoptosis due to internucleosomal cleavage by endonucleases. **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. 65-67.

Question 1135: Which amongst the following is characteristic of a carcinoma?

A. Cytokeratin (Correct Answer)
B. Vimentin
C. Calretinin
D. CD45

Explanation: **Explanation:** The identification of tumors using **Immunohistochemistry (IHC)** is a high-yield topic for NEET-PG. IHC relies on the expression of specific intermediate filaments that reflect the cell of origin. [1] **Why Cytokeratin is correct:** **Cytokeratin** is the characteristic intermediate filament found in **epithelial cells**. Since **Carcinomas** are malignant tumors arising from epithelial tissues (e.g., skin, GI tract, lung), they consistently express Cytokeratin [1]. It is the primary marker used to differentiate a poorly differentiated carcinoma from other types of malignancies [1]. **Analysis of Incorrect Options:** * **Vimentin:** This is the intermediate filament characteristic of **mesenchymal cells** [2]. It is the primary marker for **Sarcomas** (e.g., Osteosarcoma, Liposarcoma) [1]. While some carcinomas can show focal vimentin expression during "epithelial-mesenchymal transition," it is not the defining characteristic. * **Calretinin:** This is a calcium-binding protein used as a specific marker for **Mesothelioma** (tumors of the pleura/peritoneum) and certain steroid-producing tumors like Adrenocortical carcinoma or Sex cord-stromal tumors. * **CD45 (LCA - Leukocyte Common Antigen):** This is the definitive marker for cells of hematopoietic origin. It is used to identify **Lymphomas** and Leukemias [1]. **High-Yield Clinical Pearls for NEET-PG:** * **Desmin:** Marker for Muscle tumors (Rhabdomyosarcoma, Leiomyosarcoma). * **S-100 / HMB-45:** Markers for Melanoma and Neural crest-derived tumors. * **PSA:** Marker for Prostatic Adenocarcinoma. * **Chromogranin/Synaptophysin:** Markers for Neuroendocrine tumors (e.g., Carcinoid). * **GFAP:** Marker for Glial tumors (Astrocytoma). **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. [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. 210-211.

Question 1136: In which of the following pathological processes are caspases involved?

A. Apoptosis (Correct Answer)
B. Fatty change
C. Hydropic degeneration
D. Collagen hyalinosis

Explanation: **Explanation:** **1. Why Apoptosis is Correct:** Apoptosis (programmed cell death) is fundamentally driven by a cascade of enzymes called **Caspases** (Cysteine-aspartic proteases) [1]. These exist as inactive zymogens (pro-caspases) and are activated via two pathways: * **Intrinsic (Mitochondrial) Pathway:** Triggered by the release of Cytochrome C, leading to the activation of **Caspase-9** [1]. * **Extrinsic (Death Receptor) Pathway:** Triggered by FAS-FAS ligand binding, leading to the activation of **Caspase-8 or 10** [1]. Both pathways converge on the **Executioner Caspases (3, 6, and 7)**, which cleave structural proteins and activate endonucleases to cause DNA fragmentation [1]. **2. Why Other Options are Incorrect:** * **Fatty change (Steatosis):** This is a form of reversible cell injury characterized by the abnormal accumulation of triglycerides within parenchymal cells (commonly the liver). It involves metabolic derangements, not proteolytic cascades. * **Hydropic degeneration:** Also known as cloudy swelling, this is the earliest form of reversible cell injury due to the failure of Na+/K+ ATPase pumps, leading to an influx of water. * **Collagen hyalinosis:** This refers to a descriptive histological term where tissues take on a glassy, pink, homogeneous appearance (e.g., in old scars or vascular walls in hypertension). It is an extracellular protein deposition, not an active cellular death process. **High-Yield Clinical Pearls for NEET-PG:** * **Initiator Caspases:** 8, 9, 10. * **Executioner Caspases:** 3, 6, 7 (Caspase-3 is the most important). * **Inflammatory Caspases:** 1, 4, 5 (Caspase-1 is involved in Pyroptosis). * **Marker for Apoptosis:** Annexin V (binds to Phosphatidylserine flipped to the outer membrane) and TUNEL assay (detects DNA fragmentation). **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, pp. 63-67.

Question 1137: What is an ultrastructural finding of irreversible cellular injury?

A. Ribosomal detachment from the endoplasmic reticulum
B. Amorphous densities in mitochondria (Correct Answer)
C. Formation of phagolysosomes
D. Cell swelling

Explanation: ### Explanation In cellular pathology, the transition from reversible to irreversible injury is marked by two critical phenomena: the inability to reverse mitochondrial dysfunction and profound disturbances in membrane function [2]. **Why Option B is Correct:** **Amorphous densities (flocculent densities)** within the mitochondrial matrix are the hallmark ultrastructural sign of **irreversible injury** [1]. These densities represent large aggregates of denatured proteins and precipitated calcium salts [1]. Their presence indicates that the mitochondria have suffered permanent damage and can no longer produce ATP, leading to inevitable cell death (necrosis). **Analysis of Incorrect Options:** * **A. Ribosomal detachment:** This occurs due to the swelling of the Rough Endoplasmic Reticulum (RER) when ATP-dependent ion pumps fail [5]. It leads to decreased protein synthesis but is a **reversible** change if oxygenation is restored [3]. * **C. Formation of phagolysosomes:** This is a part of the normal cellular process of autophagy or heterophagy. While it may increase during stress, it is a physiological or adaptive mechanism, not a marker of irreversible injury. * **D. Cell swelling (Hydropic change):** This is the **earliest** light microscopic manifestation of almost all forms of injury [3]. It results from the failure of the Na+/K+ ATPase pump but is entirely **reversible** [5]. **NEET-PG High-Yield Pearls:** * **Point of No Return:** The two definitive markers of irreversible injury are **Mitochondrial Vacuolization/Amorphous Densities** and **Lysosomal Rupture** (leading to enzymatic digestion of the cell) [4]. * **Reversible vs. Irreversible:** Small, "small-sized" mitochondrial densities can be seen in reversible injury; however, **large, flocculent/amorphous** densities are always irreversible. * **Nuclear Changes:** Irreversible injury is also characterized by nuclear changes: Pyknosis (shrinkage), Karyorrhexis (fragmentation), and Karyolysis (dissolution). **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, pp. 53-55. [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. 102-103. [3] 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. 61-62. [4] 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. 60-61. [5] 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. 56-57.

Question 1138: The ability of stem cells to differentiate into a cell of another lineage, expressing molecular characteristics and performing the function of the new cell type, is referred to as what?

A. Dedifferentiation
B. Redifferentiation
C. Transdifferentiation (Correct Answer)
D. Subdifferentiation

Explanation: ### Explanation **Correct Answer: C. Transdifferentiation** **Concept Overview:** Transdifferentiation is a process where a differentiated stem cell (or a somatic cell) switches its lineage to become a completely different cell type. Unlike typical differentiation, where a stem cell matures into its programmed progeny, transdifferentiation involves "crossing" lineage boundaries. The new cell expresses the molecular markers and performs the specific physiological functions of the new lineage. **Why the other options are incorrect:** * **A. Dedifferentiation:** This refers to a process where a specialized cell reverts to a more primitive, less specialized state (e.g., a mature cell becoming a stem-like cell). It is often seen in regeneration or certain neoplastic processes. * **B. Redifferentiation:** This is the process where a dedifferentiated cell matures again into a specialized cell type. * **D. Subdifferentiation:** This is not a standard pathological term used to describe lineage switching. **Clinical Pearls & High-Yield Facts for NEET-PG:** * **Classic Example:** The most common clinical example of transdifferentiation is **Barrett’s Esophagus**. Here, the chronic acid reflux causes the stratified squamous epithelium of the esophagus to change into intestinal-type columnar epithelium (containing goblet cells). * **Metaplasia vs. Transdifferentiation:** While "Metaplasia" is the clinical term for the replacement of one adult cell type with another, **transdifferentiation** is the specific cellular mechanism/reprogramming that drives this change [1]. * **Stem Cell Niche:** Transdifferentiation is often triggered by changes in the "niche" or microenvironment, leading to the activation of different sets of transcription factors [1]. * **Regenerative Medicine:** Transdifferentiation is a major area of research for converting abundant cells (like skin fibroblasts) into scarce cells (like insulin-producing beta cells) without passing through a pluripotent state. **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.

Question 1139: Increased amounts of calcium in the cytosol of an injured cell reflect a release of calcium from which intracellular organelle?

A. Peroxisomes
B. Smooth Endoplasmic Reticulum
C. Lysosomes
D. Mitochondria (Correct Answer)

Explanation: **Explanation:** In the context of cell injury, the loss of calcium homeostasis is a critical event. Intracellular cytosolic calcium is normally maintained at extremely low levels (approx. 0.1 μmol) compared to extracellular levels [1]. This gradient is maintained by ATP-dependent calcium pumps. **Why Mitochondria is the Correct Answer:** Intracellular calcium is primarily sequestered within two major organelles: the **Mitochondria** and the **Endoplasmic Reticulum (ER)** [1]. When a cell is injured (e.g., by ischemia or toxins), there is an initial release of $Ca^{2+}$ from these intracellular stores into the cytosol, followed by an influx across the plasma membrane [1]. The mitochondria serve as a significant reservoir; however, the pathological accumulation of calcium within the mitochondria itself eventually leads to the opening of the **Mitochondrial Permeability Transition Pore (MPTP)**, resulting in the failure of ATP production and the release of pro-apoptotic proteins like Cytochrome C [2]. **Analysis of Incorrect Options:** * **A. Peroxisomes:** These are involved in the catabolism of very-long-chain fatty acids and the detoxification of reactive oxygen species (ROS) via catalase; they do not store significant calcium. * **B. Smooth Endoplasmic Reticulum:** While the ER (specifically the Sarcoplasmic Reticulum in muscle) does store calcium, standard pathology texts (Robbins) emphasize that in the context of general cell injury mechanisms, the release from **Mitochondria** and ER occurs [1], but Mitochondria are often the primary focus regarding the transition from reversible to irreversible injury. *Note: If both are options, Mitochondria is traditionally the preferred answer in this specific question context.* * **C. Lysosomes:** These contain hydrolytic enzymes (acid hydrolases). While their membrane breakdown leads to enzymatic digestion of the cell (autolysis), they are not a primary storage site for calcium [3]. **NEET-PG High-Yield Pearls:** * **Irreversible Injury Marker:** Amorphous densities (flocculent densities) in the mitochondrial matrix, composed of calcium and proteins, are a hallmark of irreversible cell injury. * **Enzyme Activation:** Increased cytosolic calcium activates several damaging enzymes: **Phospholipases** (membrane damage), **Proteases** (cytoskeletal damage), **Endonucleases** (DNA fragmentation), and **ATPases** (accelerating ATP depletion) [1]. * **Dystrophic Calcification:** Occurs in necrotic/dying tissues with normal serum calcium levels. Mitochondria are the initial site of calcium crystal formation in this process. **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, pp. 57-59. [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. 102-103. [3] 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. 60-61.

Question 1140: Which of the following is a finding in lymphoid tissues in individuals with common variable hypogammaglobulinemia?

A. Decreased B cell count
B. Increased B cell count
C. Normal B cell count (Correct Answer)
D. Absent B cells

Explanation: ### Explanation **Common Variable Immunodeficiency (CVID)** is a primary immunodeficiency characterized by hypogammaglobulinemia (low IgG, IgA, and often IgM) and a failure of B cells to differentiate into plasma cells [1]. **Why Option C is Correct:** The hallmark of CVID is a **normal or near-normal number of circulating B cells** [1]. The defect is not in the production of B cells (which occurs in the bone marrow), but in their **maturation into antibody-secreting plasma cells** [1]. Because B cells are present but dysfunctional, the lymphoid tissues (lymph nodes, spleen, and Peyer’s patches) typically show preserved or even hyperplastic B-cell areas, though they lack mature plasma cells. **Why Other Options are Incorrect:** * **Options A, B, and D:** These are incorrect because CVID is defined by a functional defect rather than a quantitative deficiency of B cells. A **decrease or absence of B cells (Option A and D)** is characteristic of **X-linked Agammaglobulinemia (Bruton’s)**, where a mutation in the BTK gene prevents B cell maturation from the pre-B stage [1]. An **increased B cell count (Option B)** is not a feature of primary immunodeficiency and would more likely suggest a lymphoproliferative disorder. **High-Yield Clinical Pearls for NEET-PG:** * **Age of Onset:** Unlike Bruton’s (infancy), CVID typically presents in the **2nd or 3rd decade** of life (late teens/young adults). * **Clinical Features:** Recurrent sinopulmonary infections (H. influenzae, S. pneumoniae) and chronic diarrhea (often due to *Giardia lamblia*). * **Associated Risks:** High risk of **autoimmune diseases** (e.g., Pernicious anemia, RA) and **malignancies** (especially B-cell lymphomas and gastric carcinoma). * **Pathology:** Lymph nodes may show **hyperplastic lymphoid follicles** (paradoxical follicular hyperplasia) due to the body's attempt to stimulate the dysfunctional B cells. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 249-250.

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Cell Injury and Cell Death

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Adaptations of Cellular Growth

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Accumulations and Deposits

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Acute and Chronic Inflammation

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Tissue Repair and Wound Healing

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Hemodynamic Disorders

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Genetic Disorders

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Environmental Pathology

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Nutritional Diseases

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Molecular Basis of Disease

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