FMGE 2025 Practice Questions

Q: A patient presents with multiple colonic polyps and has been diagnosed with colorectal carcinoma. There is a strong family history of Hereditary Non-Polyposis Colorectal Cancer (HNPCC). Which DNA repair mechanism is most likely defective in this condition?

Mismatch repair. ***Mismatch repair***- **HNPCC (Lynch syndrome)** is caused by inherited germline mutations in genes (e.g., *MLH1*, *MSH2*) that are responsible for the **mismatch repair (MMR)** pathway. - The failure of MMR leads to the accumulation of errors, specifically in repetitive DNA sequences, resulting in **microsatellite instability** which drives carcinogenesis.*Nucleotide excision repair*- This mechanism repairs bulky helix-distorting lesions in DNA, most commonly **pyrimidine dimers** caused by UV radiation. - A classic disease associated with defective **NER** is **Xeroderma Pigmentosum**, which presents with extreme sun sensitivity and a high risk of skin cancers.*Base excision repair*- This pathway primarily corrects small, non-helix distorting damage, such as oxidized or alkylated bases, utilizing enzymes like **DNA glycosylases**.- While fundamental for DNA maintenance, primary defects in BER are not the underlying cause of pathogenesis in **Lynch syndrome**.*Double-strand break repair*- This mechanism repairs severe damage where the entire DNA helix is broken, typically via **Homologous Recombination (HR)** or **Non-Homologous End Joining (NHEJ)**. - Defects in HR are often linked to hereditary breast and ovarian cancers (e.g., *BRCA1*/ *BRCA2* mutations) and are distinct from the pathogenesis of **HNPCC**.

Q: A man presents with high VLDL and chylomicrons, with eruptive xanthomas. What is the most likely diagnosis?

Familial hypertriglyceridemia. ***Familial hypertriglyceridemia (Type IV or V hyperlipidemia)*** - This condition presents with **elevated VLDL and chylomicrons**, causing severe hypertriglyceridemia [1] - **Eruptive xanthomas** are pathognomonic for triglyceride levels >1000 mg/dL, appearing as small yellow papules on extensor surfaces and buttocks - Patients are at risk for **acute pancreatitis** due to extreme triglyceride elevation - Treatment includes **fibrates, omega-3 fatty acids, and strict dietary fat restriction** [2] *Familial hyperlipidemia* - This is a non-specific term that could refer to any inherited lipid disorder - Not a precise diagnostic entity used in clinical practice *Familial dysbetalipoproteinemia (Type III)* - Characterized by elevated **IDL (intermediate-density lipoproteins)**, not primarily VLDL + chylomicrons [1] - Presents with **palmar xanthomas (yellowish discoloration of palmar creases)** and tuberoeruptive xanthomas [1] - Different lipid pattern and xanthoma distribution than described *Familial hypercholesterolemia* - Characterized by elevated **LDL cholesterol**, not triglycerides [1] - Presents with **tendinous xanthomas, xanthelasma, and corneal arcus** [1] - Does not cause eruptive xanthomas or chylomicronemia

Q: What is the primary protein that binds to thyroxine?

Thyroxine-binding globulin. ***Thyroxine-binding globulin*** - **TBG** is a single chain glycoprotein that is the primary transporter, binding approximately 70-80% of circulating **T4** (thyroxine) and a smaller proportion of T3. - It serves as a high-affinity reservoir, maintaining hormonal homeostasis and contributing to the long **half-life** of T4. *Follistatin* - **Follistatin** binds and inhibits the activity of **activin** and is primarily involved in regulating the release of **FSH** (follicle-stimulating hormone) from the pituitary. - It has no functional role in the systemic transport or binding of thyroid hormones. *Transthyretin* - **Transthyretin** (or prealbumin) is the second most abundant carrier, binding about 10-15% of circulating T4, and is the principal carrier of **retinol** (Vitamin A). - Although it transports T4, its binding affinity and capacity are significantly lower than those of **TBG**, thus it is not the primary binder. *Transferrin* - **Transferrin** is the main plasma protein responsible for transporting **ferric iron (Fe3+)** throughout the body. - Its binding specificity is strictly for iron and does not involve the transport of **thyroxine**.

Q: Which vitamin deficiency can lead to lactic acidosis?

Thiamine. ***Thiamine*** - **Thiamine (Vitamin B1)** is a crucial cofactor for the enzyme **pyruvate dehydrogenase (PDH)**, which converts **pyruvate** to **acetyl-CoA** to enter the Krebs cycle. - When thiamine is deficient, pyruvate cannot be processed efficiently, leading to its accumulation and subsequent shunting into **lactate** via **lactate dehydrogenase**, thus causing **lactic acidosis**, characteristic of **beriberi**. *Riboflavin* - Riboflavin (Vitamin B2) is a precursor for the coenzymes **FAD** and **FMN**, essential for redox reactions, but its deficiency symptoms mainly involve the oral cavity and skin. - Deficiency leads to **angular cheilitis**, **glossitis**, and **corneal vascularization**, and is not the direct cause of severe lactic acidosis. *Niacin* - Niacin (Vitamin B3) is a precursor for **NAD+** and **NADP+**, vital for many metabolic reactions. - Deficiency causes **pellagra**, characterized by the 3 D's: **Dermatitis**, **Diarrhea**, and **Dementia**, not primarily lactic acidosis. *Biotin* - Biotin (Vitamin B7) acts as a coenzyme for **carboxylase enzymes** (e.g., pyruvate carboxylase, acetyl-CoA carboxylase), which are necessary for gluconeogenesis and fatty acid synthesis. - While **pyruvate carboxylase** uses biotin, thiamine deficiency specifically impairs the key step of converting pyruvate to acetyl-CoA (via PDH complex), making it the primary cause of vitamin-deficiency-related lactic acidosis.

Q: Which opportunistic pathogen demonstrates a “crushed ping pong ball appearance” on Gomori methenamine stain?

Pneumocystis jirovecii. ***Pneumocystis jirovecii*** - This opportunistic fungus classically appears as collapsed, crescent-shaped cysts on **Gomori methenamine silver (GMS) stain**, giving it the pathognomonic **“crushed ping pong ball”** appearance. - It is a common cause of **Pneumocystis pneumonia (PCP)** in immunocompromised individuals, particularly those with advanced HIV infection, and is typically found in the alveolar spaces. *Histoplasma capsulatum* - This dimorphic fungus appears as small, oval yeasts that are characteristically found **intracellularly within macrophages**. - It does not form the collapsed cysts seen with *P. jirovecii* and lacks the “crushed ping pong ball” morphology. *Cryptococcus neoformans* - This yeast is distinguished by its thick **polysaccharide capsule**, which creates a clear halo around the organism on **India ink stain**. - While it can be stained with GMS, it appears as a budding yeast and does not exhibit the collapsed cyst morphology. *Aspergillus fumigatus* - This mold is identified by its characteristic **septate hyphae** that branch at **acute (45-degree) angles**. - It does not form cysts in tissue and has a filamentous structure, which is entirely different from the appearance of *P. jirovecii*.

Q: Which antibody is the first to appear and acts fastest during a primary (first) immune response to an infection?

IgM. ***IgM***- **IgM** is the first antibody isotype produced and secreted by **plasma B cells** following initial exposure to an antigen (primary immune response).- Because it is a **pentamer** (five Y-shaped units), IgM has 10 binding sites, giving it superior efficiency in complement activation, agglutination, and acting as the immediate responder.*IgG*- **IgG** is the most abundant immunoglobulin in the serum and generally appears later than IgM during the primary response.- It is the predominant antibody during the **secondary immune response**, providing long-term immunity and crossing the **placenta**.*IgE*- **IgE** is associated primarily with the initiation of **Type I hypersensitivity reactions** (allergies) by binding to mast cells and basophils.- It is also critical for defense against **helminthic parasites** but is not the first antibody in standard acute infection.*IgA*- **IgA** functions primarily in **mucosal immunity**, being secreted as a dimer into milk, saliva, tears, and mucosal linings (e.g., gut and respiratory tract).- While vital for preventing pathogen entry, it does not lead the kinetics of the initial systemic antibody response.

Q: Chocolate agar is primarily used for the isolation of which of the following organisms?

Haemophilus influenzae. ***Haemophilus influenzae*** - *H. influenzae* is a **fastidious** organism requiring **X factor (hemin)** and **V factor (NAD/NADH)** for growth, both of which are supplied by the lysed red blood cells in chocolate agar. - Chocolate agar is essentially **heated blood agar** where the red blood cells have lysed, releasing essential growth factors required by organisms like *Haemophilus spp*. *Listeria monocytogenes* - *Listeria monocytogenes* is a **non-fastidious** organism that typically grows well on routine sheep **Blood Agar** (often showing weak beta-hemolysis). - Isolation of *Listeria* often utilizes cold enrichment or specialized selective media like **Oxford agar** or **PALCAM agar**. *Streptococcus pneumoniae* - *S. pneumoniae* typically grows well on routine **Blood Agar**, where it exhibits characteristic **alpha-hemolysis** (partial lysis resulting in a green discoloration). - While it can grow on chocolate agar, it does not require the specific X and V factors released, making Blood Agar the standard medium for its isolation. *Escherichia coli* - *E. coli* is a non-fastidious, common enteric bacterium that grows easily on non-enriched media like **Nutrient agar**. - It is typically identified using selective and differential media such as **MacConkey agar** (lactose-fermenting pink colonies) or Eosin Methylene Blue (EMB) agar.

Q: After the parotidectomy operation, a patient presents with excessive sweating and redness over the parotid region. What is the diagnosis?

Frey’s Syndrome. ***Frey’s Syndrome***- It is a common post-parotidectomy complication resulting from **aberrant regeneration** of the severed **auriculotemporal nerve**.- The parasympathetic secretomotor fibers meant for the parotid gland mistakenly reinnervate the overlying cutaneous sweat glands and blood vessels, causing **gustatory sweating** and **flushing (redness)** in the parotid region upon chewing or eating.*Horner’s syndrome*- This syndrome results from interruption of the **cervical sympathetic trunk** and presents with the classic triad of **ptosis** (droopy eyelid), **miosis** (constricted pupil), and **anhidrosis** (lack of sweating) on the affected side of the face.- It is unrelated to the auriculotemporal nerve damage common after parotidectomy and involves *lack* of sweating, contrary to the patient's complaint of *excessive* sweating.*Bell’s Palsy*- This is an **idiopathic acute peripheral facial nerve palsy**, leading to unilateral weakness or paralysis of the muscles of facial expression (e.g., inability to close the eye or raise the eyebrow).- While the facial nerve (CN VII) is at risk during parotidectomy, Bell's Palsy itself does not account for the specific symptoms of post-operative gustatory sweating and redness.*Glossopharyngeal neuralgia*- This condition involves brief, severe episodes of stabbing pain in the throat, tonsillar area, back of the tongue, or ear due to irritation of the **glossopharyngeal nerve (CN IX)**.- It is a disorder characterized purely by pain, often triggered by **swallowing** or **talking**, and is not associated with post-operative salivary gland complication symptoms like gustatory sweating.

Question 1

A patient presents with multiple colonic polyps and has been diagnosed with colorectal carcinoma. There is a strong family history of Hereditary Non-Polyposis Colorectal Cancer (HNPCC). Which DNA repair mechanism is most likely defective in this condition?

Accepted Answer

Mismatch repair

Answer

Double-strand break repair

Answer

Nucleotide excision repair

Answer

Base excision repair

Question 2

A man presents with high VLDL and chylomicrons, with eruptive xanthomas. What is the most likely diagnosis?

Accepted Answer

Familial hypertriglyceridemia

Answer

Familial hyperlipidemia

Answer

Familial dysbetalipoproteinemia

Answer

Familial hypercholesterolemia

Question 3

What is the primary protein that binds to thyroxine?

Accepted Answer

Thyroxine-binding globulin

Answer

Follistatin

Answer

Transthyretin

Answer

Transferrin

Question 4

A breastfed infant presents with lethargy, hepatomegaly, and cataracts. Which of the following enzyme deficiencies is most likely responsible for this presentation?

Accepted Answer

Galactose-1-phosphate uridyltransferase (GALPUT)

Answer

Galactokinase

Answer

Aldolase B

Answer

Fructokinase

Question 5

Which vitamin deficiency can lead to lactic acidosis?

Accepted Answer

Thiamine

Answer

Riboflavin

Answer

Niacin

Answer

Biotin

Question 6

Which opportunistic pathogen demonstrates a “crushed ping pong ball appearance” on Gomori methenamine stain?

Accepted Answer

Pneumocystis jirovecii

Answer

Cryptococcus neoformans

Answer

Aspergillus fumigatus

Answer

Histoplasma capsulatum

Question 7

Which antibody is the first to appear and acts fastest during a primary (first) immune response to an infection?

Accepted Answer

IgM

Answer

IgE

Answer

IgA

Answer

IgG

Question 8

Chocolate agar is primarily used for the isolation of which of the following organisms?

Accepted Answer

Haemophilus influenzae

Answer

Listeria monocytogenes

Answer

Streptococcus pneumoniae

Answer

Escherichia coli

Question 9

In malignant hyperthermia, a genetic mutation in the ryanodine receptor (RYR1) leads to a life-threatening reaction to certain anesthetic agents. What is the primary ionic abnormality caused by this receptor defect?

Accepted Answer

Increased calcium release from the sarcoplasmic reticulum

Answer

Increased sodium influx into the muscle cell

Answer

Increased potassium uptake into the sarcoplasmic reticulum

Answer

Increased chloride efflux from the muscle cell

Question 10

After the parotidectomy operation, a patient presents with excessive sweating and redness over the parotid region. What is the diagnosis?

Accepted Answer

Frey’s Syndrome

Answer

Bell’s Palsy

Answer

Glossopharyngeal neuralgia

Answer

Horner’s syndrome

FMGE 2025

Biochemistry

Microbiology

Physiology

Surgery