Genetic Disorders and Biochemical Pathology — MCQs

Genetic Disorders and Biochemical Pathology Indian Medical PG Practice Questions and MCQs

Question 541: What is the genotype of Klinefelter syndrome?

A. 45X0
B. 47XXX
C. 47XXY (Correct Answer)
D. Trisomy 13

Explanation: **Explanation:** **Correct Answer: C. 47XXY** Klinefelter syndrome is the most common sex chromosome disorder affecting males (incidence approx. 1:600). It occurs due to **nondisjunction** of sex chromosomes during meiosis, resulting in an extra X chromosome. The presence of the Y chromosome (SRY gene) ensures a male phenotype, but the extra X chromosome leads to testicular dysgenesis and primary hypogonadism. **Analysis of Incorrect Options:** * **A. 45X0 (Turner Syndrome):** This is the most common sex chromosome abnormality in females, characterized by short stature, webbed neck, and streak ovaries. * **B. 47XXX (Triple X Syndrome):** A female phenotype often associated with tall stature and mild cognitive delays, but frequently asymptomatic. * **C. Trisomy 13 (Patau Syndrome):** An autosomal trisomy characterized by severe midline defects, including holoprosencephaly, cleft lip/palate, and polydactyly. **High-Yield Clinical Pearls for NEET-PG:** * **Clinical Features:** Tall stature, long extremities, gynecomastia, small firm testes (testicular atrophy), and female-type hair distribution. * **Biochemical Profile:** Low Testosterone, **Elevated LH and FSH** (due to loss of feedback inhibition), and elevated Estradiol. * **Histopathology:** Hyalinization and fibrosis of seminiferous tubules and **Leydig cell hyperplasia** (compensatory). * **Complications:** Increased risk of male breast cancer, extragonadal germ cell tumors, and autoimmune diseases (e.g., SLE). * **Barr Body:** Unlike normal males, Klinefelter patients are **Barr body positive** (calculated as Number of X chromosomes minus 1).

Question 542: Bronze diabetes is seen in which of the following conditions?

A. Wilson's disease
B. Sarcoidosis
C. Lead intoxication
D. Hemochromatosis (Correct Answer)

Explanation: **Explanation:** **Bronze Diabetes** is the classic clinical triad of **hyperpigmentation, diabetes mellitus, and cirrhosis**, specifically associated with **Hereditary Hemochromatosis**. 1. **Why Hemochromatosis is correct:** Hemochromatosis is an autosomal recessive disorder (most commonly a mutation in the **HFE gene**) leading to excessive intestinal iron absorption. The excess iron is deposited as **hemosiderin** in various organs. * **Skin:** Iron deposition and increased melanin production cause a "bronze" metallic tint. * **Pancreas:** Iron deposition in the islets of Langerhans causes selective destruction of beta cells, leading to secondary diabetes mellitus. * **Liver:** Leads to micronodular cirrhosis and increases the risk of Hepatocellular Carcinoma (HCC). 2. **Why other options are incorrect:** * **Wilson’s Disease:** A disorder of copper metabolism. While it affects the liver and brain (basal ganglia), it typically presents with Kayser-Fleischer (KF) rings and neurological symptoms, not bronze skin or diabetes. * **Sarcoidosis:** A granulomatous disease that can affect the pancreas, but it is a rare cause of diabetes and does not cause the characteristic bronze pigmentation. * **Lead Intoxication:** Presents with abdominal pain (colic), peripheral neuropathy (wrist drop), and "Burtonian lines" on gums, but does not involve iron-related skin or pancreatic pathology. **High-Yield Clinical Pearls for NEET-PG:** * **Gold Standard Diagnosis:** Liver biopsy with **Prussian Blue staining** (to quantify the Hepatic Iron Index). * **Screening Test of Choice:** Transferrin saturation (increased) and Serum Ferritin. * **Treatment:** Therapeutic phlebotomy is the mainstay; iron chelators (e.g., Deferoxamine) are used if phlebotomy is contraindicated. * **Other associations:** Dilated cardiomyopathy and "Pseudogout" (Calcium pyrophosphate deposition).

Question 543: Which cell organelle is affected in Wolman’s Disease?

A. Peroxisome
B. Lysosome (Correct Answer)
C. Liposome
D. Dictyosome

Explanation: **Explanation:** **Wolman’s Disease** is a severe, autosomal recessive **Lysosomal Storage Disorder (LSD)**. It is caused by a deficiency of the enzyme **Lysosomal Acid Lipase (LAL)**. Under normal physiological conditions, this enzyme is responsible for hydrolyzing cholesteryl esters and triglycerides within the **lysosome**. In its absence, these lipids accumulate massively in the lysosomes of various tissues (liver, spleen, and adrenal glands), leading to multi-organ failure. **Analysis of Options:** * **Option B (Lysosome):** This is the correct site of pathology. The LAL enzyme deficiency leads to the entrapment of lipids inside the lysosomal compartment, characterizing it as a classic LSD. * **Option A (Peroxisome):** Peroxisomes are involved in long-chain fatty acid oxidation (beta-oxidation). Disorders related to peroxisomes include Zellweger Syndrome and Adrenoleukodystrophy, not Wolman’s. * **Option C (Liposome):** Liposomes are artificial spherical vesicles used primarily for drug delivery; they are not naturally occurring functional organelles involved in this disease pathology. * **Option D (Dictyosome):** This is another term for the stacks of the Golgi apparatus, which is involved in protein packaging and modification, not the primary site of lipid hydrolysis. **High-Yield Clinical Pearls for NEET-PG:** * **Pathognomonic Sign:** Bilateral **adrenal calcification** is a classic radiological finding in Wolman’s Disease. * **Clinical Presentation:** Hepatomegaly, splenomegaly, steatorrhea, and failure to thrive in infancy. * **Spectrum:** **Cholesteryl Ester Storage Disease (CESD)** is a milder, later-onset form of LAL deficiency compared to the infantile-onset Wolman’s Disease. * **Treatment:** Enzyme replacement therapy (Sebelipase alfa) is now available.

Question 544: A 2-month-old infant presents with failure to thrive, recurrent emesis, hepatosplenomegaly, and adrenal insufficiency. Adrenal calcification is noted radiologically. What is the most likely diagnosis?

A. Adrenal hemorrhage
B. Wolman's disease (Correct Answer)
C. Pheochromocytoma
D. Addison's disease

Explanation: ### Explanation **Correct Answer: B. Wolman’s disease** **Underlying Concept:** Wolman’s disease is a severe, early-onset lysosomal storage disorder caused by a deficiency of **Lysosomal Acid Lipase (LAL)**. This enzyme is responsible for hydrolyzing cholesteryl esters and triglycerides. Its deficiency leads to the massive accumulation of these lipids in the lysosomes of various tissues, including the liver, spleen, and adrenal glands. The pathognomonic feature of Wolman’s disease is **bilateral adrenal calcification**, which occurs due to the massive deposition of lipids in the adrenal cortex, leading to necrosis and subsequent dystrophic calcification. This results in primary adrenal insufficiency (Addisonian crisis), hepatosplenomegaly, and severe malabsorption (steatorrhea), typically leading to death within the first year of life. **Why Incorrect Options are Wrong:** * **A. Adrenal hemorrhage:** While it can cause adrenal insufficiency and later calcification (Waterhouse-Friderichsen syndrome), it does not explain the hepatosplenomegaly or the progressive failure to thrive seen in this metabolic context. * **C. Pheochromocytoma:** This is a catecholamine-secreting tumor of the adrenal medulla. It presents with hypertension and tachycardia, not adrenal insufficiency or diffuse calcification in infancy. * **D. Addison’s disease:** This is a general term for primary adrenal insufficiency. While present in Wolman’s, it is a clinical finding rather than the underlying diagnosis, and it doesn't account for the hepatosplenomegaly. **High-Yield Clinical Pearls for NEET-PG:** * **Enzyme Defect:** Lysosomal Acid Lipase (LAL). * **Gene:** *LIPA* gene (Chromosome 10). * **Radiological Hallmark:** Bilateral, enlarged, bell-shaped adrenal calcifications. * **Cholesteryl Ester Storage Disease (CESD):** A milder, later-onset variant of LAL deficiency where adrenal calcification is rare. * **Treatment:** Enzyme replacement therapy (Sebelipase alfa).

Question 545: NARP syndrome is a type of:

A. Mitochondrial function disorder (Correct Answer)
B. Glycogen storage disorder
C. Lysosomal storage disorder
D. Lipid storage disorder

Explanation: **Explanation** **NARP syndrome** (Neurogenic muscle weakness, Ataxia, and Retinitis Pigmentosa) is a classic example of a **mitochondrial function disorder**. It is caused by a point mutation in the **MT-ATP6 gene**, which encodes a subunit of the mitochondrial ATP synthase (Complex V). This mutation disrupts the oxidative phosphorylation pathway, leading to a deficit in ATP production that primarily affects high-energy-demand tissues like the nervous system and retina. **Why other options are incorrect:** * **Glycogen storage disorders (GSDs):** These are caused by deficiencies in enzymes involved in glycogen synthesis or breakdown (e.g., Von Gierke or Pompe disease), primarily affecting the liver and skeletal muscles. * **Lysosomal storage disorders (LSDs):** These result from defects in lysosomal acid hydrolases (e.g., Gaucher or Tay-Sachs disease), leading to the accumulation of undigested macromolecules. * **Lipid storage disorders:** These involve the abnormal accumulation of lipids (e.g., Niemann-Pick disease) due to enzymatic failures in lipid metabolism, distinct from mitochondrial DNA mutations. **High-Yield Clinical Pearls for NEET-PG:** * **Maternal Inheritance:** Like most mitochondrial diseases, NARP is inherited exclusively from the mother. * **Heteroplasmy:** The severity of NARP depends on the ratio of mutant to wild-type mitochondrial DNA within cells. * **Leigh Syndrome Link:** If the MT-ATP6 mutation load is very high (>90%), the clinical phenotype shifts from NARP to the more severe **Maternally Inherited Leigh Syndrome (MILS)**, characterized by infantile necrotizing encephalopathy. * **Key Triad:** Always look for the combination of **Proximal neurogenic muscle weakness**, **Ataxia**, and **Salt-and-pepper retinopathy** in clinical vignettes.

Question 546: Wilson disease is due to the accumulation of which element?

A. Copper (Correct Answer)
B. Iron
C. Zinc
D. Nickel

Explanation: **Explanation:** **Wilson Disease (Hepatolenticular Degeneration)** is an autosomal recessive disorder caused by a mutation in the **ATP7B gene** located on chromosome 13. This gene encodes a copper-transporting P-type ATPase. **1. Why Copper is Correct:** In a healthy individual, ATP7B is responsible for incorporating copper into apoceruloplasmin to form **ceruloplasmin** and facilitating the excretion of excess copper into the bile. In Wilson disease, this mechanism fails, leading to the toxic accumulation of **Copper** in various tissues, primarily the **liver** (cirrhosis), **brain** (basal ganglia/lenticular nucleus degeneration), and the **cornea** (Kayser-Fleischer rings). **2. Why Other Options are Incorrect:** * **Iron:** Accumulation of iron leads to **Hemochromatosis**, characterized by the "bronze diabetes" triad (pigmentation, diabetes, and cirrhosis). * **Zinc:** Zinc is actually used as a **treatment** for Wilson disease because it induces metallothionein in intestinal cells, which sequesters copper and prevents its absorption. * **Nickel:** While nickel can be toxic in industrial settings, it is not associated with a specific primary genetic storage disorder like Wilson disease. **3. High-Yield Clinical Pearls for NEET-PG:** * **Diagnosis:** Low serum ceruloplasmin, increased urinary copper excretion, and increased hepatic copper content (Gold Standard). * **Ocular Sign:** **Kayser-Fleischer (KF) rings** (copper deposition in the Descemet’s membrane). * **Neurological Sign:** "Giant Panda Face" appearance on MRI of the midbrain. * **Treatment:** Chelating agents like **D-Penicillamine** or Trientine, and Zinc for maintenance.

Question 547: What is true about linkage analysis in familial gene disorders?

A. Useful to create a pedigree chart to show affected and non-affected family members.
B. Used to create a pedigree chart to show non-paternity.
C. A characteristic DNA polymorphism in a family is associated with the disorder. (Correct Answer)
D. Pedigree charts are used to identify disease frequency.

Explanation: ### Explanation **Linkage analysis** is an indirect method of genetic diagnosis used to track a disease-causing gene within a family. It relies on the principle that genes or DNA sequences located close to each other on the same chromosome are likely to be inherited together (co-segregate) during meiosis. **Why Option C is correct:** In linkage analysis, clinicians look for a **DNA polymorphism** (a genetic marker like an RFLP, SNP, or microsatellite) that is consistently inherited alongside the disease trait in a specific family. This marker acts as a "proxy" for the defective gene. If an individual in that family possesses the specific polymorphism, they are highly likely to have the disease-causing mutation, even if the exact mutation itself has not been sequenced. **Why other options are incorrect:** * **Options A & D:** Pedigree charts are tools used to visualize inheritance patterns (Autosomal Dominant, Recessive, etc.) and calculate recurrence risks, but they do not constitute "linkage analysis" itself. Linkage analysis requires molecular data (DNA markers), not just clinical observation. * **Option B:** While DNA markers can be used in paternity testing, the primary goal of linkage analysis in medical genetics is to track disease alleles, not to establish non-paternity. **Clinical Pearls for NEET-PG:** * **Recombination Frequency:** The closer the marker is to the gene, the lower the chance of recombination, making the test more accurate. * **LOD Score (Logarithm of Odds):** A LOD score of **≥ +3.0** is the gold standard for confirming genetic linkage (1000:1 odds in favor of linkage). A score of **≤ -2.0** excludes linkage. * **Requirement:** Unlike direct mutation analysis, linkage analysis requires DNA samples from multiple family members (affected and unaffected) to be informative.

Question 548: Glucosylceramide is accumulated in which of the following conditions?

A. Tay-Sachs disease
B. Krabbe's disease
C. Gaucher's disease (Correct Answer)
D. Niemann-Pick disease

Explanation: **Explanation:** **Gaucher’s disease** is the correct answer because it is a lysosomal storage disorder caused by a deficiency of the enzyme **$\beta$-glucocerebrosidase** (also known as acid $\beta$-glucosidase). Under normal physiological conditions, this enzyme cleaves **glucosylceramide** (glucocerebroside) into glucose and ceramide. In its absence, glucosylceramide accumulates within the lysosomes of macrophages, transforming them into characteristic **"Gaucher cells"** (described as having a "wrinkled tissue paper" appearance). **Analysis of Incorrect Options:** * **Tay-Sachs disease:** Caused by a deficiency of **Hexosaminidase A**, leading to the accumulation of **$GM_2$ gangliosides**. It is clinically characterized by a cherry-red spot on the macula and the absence of hepatosplenomegaly. * **Krabbe's disease:** Caused by a deficiency of **Galactocerebrosidase**, leading to the accumulation of **galactosylceramide** and psychosine. It is marked by the presence of multinucleated globoid cells. * **Niemann-Pick disease:** Caused by a deficiency of **Sphingomyelinase**, leading to the accumulation of **sphingomyelin**. It features "foam cells" (lipid-laden macrophages) and hepatosplenomegaly. **High-Yield NEET-PG Pearls:** * **Gaucher’s Disease** is the **most common** lysosomal storage disorder. * **Clinical Triad:** Hepatosplenomegaly, bone involvement (Erlenmeyer flask deformity, aseptic necrosis of the femur), and pancytopenia. * **Biomarker:** Elevated levels of **serum chitotriosidase** are used for diagnosis and monitoring. * **Treatment:** Enzyme Replacement Therapy (ERT) with Recombinant glucocerebrosidase (Imiglucerase).

Question 549: Which condition is characterized by the odor of rotting fish in urine?

A. Hawkinsinuria
B. Phenylketonuria
C. Maple syrup urine disease (MSUD)
D. Trimethylaminuria (Correct Answer)

Explanation: **Explanation:** **Trimethylaminuria (Option D)**, also known as **"Fish Odor Syndrome,"** is the correct answer. This condition is caused by a deficiency of the enzyme **Flavin-containing monooxygenase 3 (FMO3)**. Normally, FMO3 converts trimethylamine (TMA)—a volatile, pungent compound produced by gut bacteria from precursors like choline and carnitine—into the odorless trimethylamine N-oxide (TMAO). In its absence, TMA accumulates and is excreted in sweat, breath, and urine, imparting a characteristic **rotting fish odor**. **Analysis of Incorrect Options:** * **Hawkinsinuria (Option A):** A rare defect in tyrosine metabolism (4-hydroxyphenylpyruvate dioxygenase deficiency) characterized by the excretion of hawkinsin. It typically presents with a **swimming pool or chlorine-like odor**. * **Phenylketonuria (Option B):** Caused by a deficiency of phenylalanine hydroxylase. The accumulation of phenylacetic acid leads to a classic **mousy or musty odor**. * **Maple Syrup Urine Disease (Option C):** Caused by a deficiency of the Branched-Chain Alpha-Keto Acid Dehydrogenase (BCKAD) complex. The accumulation of isoleucine leads to a **burnt sugar or maple syrup odor**. **High-Yield Clinical Pearls for NEET-PG:** * **Isovaleric Acidemia:** Sweaty feet/Cheesy odor. * **Tyrosinemia Type 1:** Cabbage-like or rancid butter odor. * **Hypermethioninemia:** Boiled cabbage odor. * **Glutaric Acidemia (Type II):** Sweaty feet odor. * **Management of Trimethylaminuria:** Dietary restriction of choline-rich foods (eggs, legumes, fish) and short courses of antibiotics (neomycin/metronidazole) to reduce gut flora.

Question 550: Which of the following vitamins is used in the treatment of Alkaptonuria?

A. Vitamin A
B. Vitamin C (Correct Answer)
C. Vitamin D
D. Vitamin K

Explanation: ### Explanation **Correct Option: B (Vitamin C)** Alkaptonuria is an autosomal recessive disorder caused by a deficiency of the enzyme **Homogentisate oxidase**, leading to the accumulation of Homogentisic Acid (HGA). Vitamin C (Ascorbic Acid) is used in management for two primary reasons: 1. **Inhibition of Oxidation:** It prevents the oxidation of Homogentisic acid into **Benzoquinone acetate**, the pigmented polymer responsible for tissue damage. 2. **Reduction of Ochronosis:** By inhibiting this polymerization, it slows down the deposition of dark pigments in connective tissues (ochronosis), thereby delaying the progression of ochronotic arthritis. **Why Other Options are Incorrect:** * **Vitamin A:** Primarily involved in vision (rhodopsin synthesis) and epithelial integrity; it has no role in the tyrosine metabolic pathway. * **Vitamin D:** Essential for calcium and phosphate homeostasis; its deficiency leads to Rickets/Osteomalacia, but it does not affect HGA metabolism. * **Vitamin K:** Acts as a co-factor for the gamma-carboxylation of clotting factors (II, VII, IX, X); it does not influence the catabolism of aromatic amino acids. **High-Yield Clinical Pearls for NEET-PG:** * **Classic Triad:** Homogentisic aciduria (urine turns black on standing/alkalinization), Ochronosis (bluish-black pigmentation of cartilage/sclera), and Arthritis (large joints). * **Diagnosis:** Ferric chloride test (transient deep blue color) and Silver nitrate test. * **Definitive Treatment:** **Nitisinone** (inhibits 4-hydroxyphenylpyruvate dioxygenase), which reduces the production of HGA. * **Dietary Advice:** Restriction of Phenylalanine and Tyrosine.

Practice by Chapter

Single Gene Disorders

Practice Questions

Biochemical Diagnosis of Genetic Disorders

Practice Questions

Inborn Errors of Metabolism

Practice Questions

Lysosomal Storage Diseases

Practice Questions

Glycogen Storage Diseases

Practice Questions

Disorders of Lipoprotein Metabolism

Practice Questions

Disorders of Purine and Pyrimidine Metabolism

Practice Questions

Hemoglobinopathies

Practice Questions

Porphyrias

Practice Questions

Biochemical Markers for Disease Diagnosis

Practice Questions

Newborn Screening for Genetic Disorders

Practice Questions

Enzyme Replacement Therapy

Practice Questions

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