Genetic Disorders and Biochemical Pathology Practice Questions

Q: What is the genotype of Klinefelter syndrome?

47XXY. **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).

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

Hemochromatosis. **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).

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

Lysosome. **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.

Q: NARP syndrome is a type of:

Mitochondrial function disorder. **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.

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

Copper. **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.

Q: Glucosylceramide is accumulated in which of the following conditions?

Gaucher's disease. **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).

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

Trimethylaminuria. **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.

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

Vitamin C. ### 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.

Question 1

What is the genotype of Klinefelter syndrome?

Accepted Answer

47XXY

Answer

45X0

Answer

47XXX

Answer

Trisomy 13

Question 2

Bronze diabetes is seen in which of the following conditions?

Accepted Answer

Hemochromatosis

Answer

Wilson's disease

Answer

Sarcoidosis

Answer

Lead intoxication

Question 3

Which cell organelle is affected in Wolman’s Disease?

Accepted Answer

Lysosome

Answer

Peroxisome

Answer

Liposome

Answer

Dictyosome

Question 4

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?

Accepted Answer

Wolman's disease

Answer

Adrenal hemorrhage

Answer

Pheochromocytoma

Answer

Addison's disease

Question 5

NARP syndrome is a type of:

Accepted Answer

Mitochondrial function disorder

Answer

Glycogen storage disorder

Answer

Lysosomal storage disorder

Answer

Lipid storage disorder

Question 6

Wilson disease is due to the accumulation of which element?

Accepted Answer

Copper

Answer

Iron

Answer

Zinc

Answer

Nickel

Question 7

What is true about linkage analysis in familial gene disorders?

Accepted Answer

A characteristic DNA polymorphism in a family is associated with the disorder.

Answer

Useful to create a pedigree chart to show affected and non-affected family members.

Answer

Used to create a pedigree chart to show non-paternity.

Answer

Pedigree charts are used to identify disease frequency.

Question 8

Glucosylceramide is accumulated in which of the following conditions?

Accepted Answer

Gaucher's disease

Answer

Tay-Sachs disease

Answer

Krabbe's disease

Answer

Niemann-Pick disease

Question 9

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

Accepted Answer

Trimethylaminuria

Answer

Hawkinsinuria

Answer

Phenylketonuria

Answer

Maple syrup urine disease (MSUD)

Question 10

Which of the following vitamins is used in the treatment of Alkaptonuria?

Accepted Answer

Vitamin C

Answer

Vitamin A

Answer

Vitamin D

Answer

Vitamin K

Genetic Disorders and Biochemical Pathology — MCQs

Genetic Disorders and Biochemical Pathology — MCQs

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