Genetic Disorders and Biochemical Pathology Practice Questions

Q: The molecule, which is the initiator of cataract formation in the eye lens and whose 1-phosphate derivative is responsible for liver failure, is:

Galacticol. **Explanation:** The correct answer is **Galacticol** (also known as Dulcitol). This question tests the biochemical pathology of **Galactosemia**, specifically the Classic form (GALT deficiency). **Why Galacticol is correct:** In patients with Galactosemia, galactose levels rise in the blood and tissues. In the lens of the eye, the enzyme **Aldose Reductase** reduces galactose into its sugar alcohol, **Galacticol**. Unlike galactose, galacticol is osmotically active and cannot diffuse out of the lens. It draws water in, causing swelling and denaturation of lens proteins, which is the **initiator of cataract formation**. Furthermore, the second part of the question refers to **Galactose-1-Phosphate**, which accumulates in Classic Galactosemia. This derivative is a potent hepatotoxin that inhibits enzymes like phosphoglucomutase, leading to **liver failure**, jaundice, and cirrhosis. **Why other options are incorrect:** * **Sorbitol:** While sorbitol causes cataracts in diabetic patients (via glucose reduction), its 1-phosphate derivative does not cause liver failure. Fructose-1-phosphate is the metabolite linked to liver issues in Fructose Intolerance. * **Mannitol:** This is an exogenous osmotic diuretic and not a metabolic intermediate that causes cataracts or liver failure. * **Inositol:** A component of phospholipids (PIP2) and a second messenger; it is not associated with these pathologies. **High-Yield Clinical Pearls for NEET-PG:** * **Classic Galactosemia:** Deficiency of Galactose-1-phosphate uridyltransferase (**GALT**). Presents with "Oil-drop" cataracts, hepatomegaly, and *E. coli* sepsis. * **Galactokinase Deficiency:** Only causes cataracts (due to galacticol) without liver or kidney damage. * **Mnemonic:** "GALT" is more severe than "GALK" because the phosphate derivative (1-P) traps energy and causes organ damage.

Q: In Wilson disease, which element is chelated?

Zinc. **Explanation:** In the context of **Wilson Disease** (Hepatolenticular degeneration), the question asks which element is **chelated** as a therapeutic intervention. While Wilson disease is a disorder of **copper** metabolism, the correct answer is **Zinc** because it acts as a pharmacological chelator/antagonist used in long-term maintenance therapy. **Why Zinc is Correct:** Zinc (usually as Zinc Acetate) induces the synthesis of **Metallothionein** in the intestinal mucosal cells. Metallothionein is an endogenous chelator that has a high affinity for copper. It binds dietary copper within the enterocytes, preventing its absorption into the portal circulation. The bound copper is then excreted safely in the feces as the intestinal cells are sloughed off. **Analysis of Incorrect Options:** * **Option A (Iron):** Iron chelation (e.g., Deferoxamine) is used in Hemochromatosis or Thalassemia, not Wilson disease. * **Option C (Copper):** Copper is the element that *accumulates* pathologically due to a mutation in the **ATP7B gene**. While drugs like D-Penicillamine and Trientine are used to chelate and excrete copper via urine, Zinc is the specific element among the options that functions as an indirect chelator/blocker of absorption. * **Option D (Selenium):** Selenium is a cofactor for Glutathione Peroxidase and has no role in the chelation therapy of Wilson disease. **NEET-PG High-Yield Pearls:** * **Gold Standard Diagnosis:** Liver biopsy (increased hepatic copper >250 μg/g dry weight). * **Screening:** Low serum Ceruloplasmin and presence of **Kayser-Fleischer (KF) rings** on slit-lamp exam. * **Treatment Triad:** 1. **D-Penicillamine:** First-line chelator (Side effect: Nephrotic syndrome, B6 deficiency). 2. **Trientine:** Preferred if Penicillamine is not tolerated. 3. **Zinc:** Best for maintenance and asymptomatic patients.

Q: What is the cause of alpha thalassemia?

Deletion of alpha genes. ### Explanation **Correct Option: A. Deletion of alpha genes** Alpha-thalassemia is primarily caused by the **deletion** of one or more of the four alpha-globin genes located on **chromosome 16**. Unlike beta-thalassemia, which usually results from point mutations, the physical loss of the gene loci via unequal crossing over during meiosis is the hallmark of this condition. The severity of the disease depends directly on the number of genes deleted (1 to 4). **Analysis of Incorrect Options:** * **B. Deletion of beta genes:** This would lead to beta-thalassemia; however, beta-thalassemia is more commonly caused by point mutations in the promoter or splicing sites rather than large deletions. * **C. Excess of alpha genes:** An excess of alpha chains occurs in **beta-thalassemia**, where the lack of beta chains leaves alpha chains unpaired. These excess alpha chains precipitate, causing hemolysis. * **D. Single amino acid substitution in alpha chain:** This describes a **hemoglobin variant** (hemoglobinopathy) rather than thalassemia. Thalassemia is a *quantitative* defect (reduced production), whereas substitutions represent a *qualitative* defect (e.g., HbS or HbC). **High-Yield Clinical Pearls for NEET-PG:** * **Genetics:** Alpha-globin cluster is on **Chromosome 16**; Beta-globin cluster is on **Chromosome 11**. * **Genotypes:** * **1 gene deletion:** Silent carrier. * **2 gene deletions:** Alpha-thalassemia trait (Microcytic anemia). * **3 gene deletions:** **HbH Disease** (Beta-tetramers, $\beta_4$). HbH forms "golf ball" inclusions on brilliant cresyl blue stain. * **4 gene deletions:** **Hb Barts** (Gamma-tetramers, $\gamma_4$). Leads to **Hydrops Fetalis**, as Hb Barts has an extremely high oxygen affinity and cannot deliver $O_2$ to tissues. * **Cis vs. Trans:** The *cis* deletion (both deletions on the same chromosome) is common in Asians and increases the risk of Hydrops Fetalis in offspring.

Q: In sickle cell anemia, what is the amino acid replacement at the beta-globin chain?

Glutamic acid by Valine in beta-6. ### Explanation **1. Understanding the Correct Answer (Option B):** Sickle cell anemia is caused by a **point mutation** (specifically a transversion) in the DNA sequence of the $\beta$-globin gene. At the **6th position** of the $\beta$-globin chain, the codon GAG (which codes for **Glutamic acid**) is mutated to GTG (which codes for **Valine**). * **Biochemical Impact:** Glutamic acid is a polar, negatively charged amino acid, whereas Valine is non-polar and hydrophobic. This substitution creates a "sticky" hydrophobic patch on the surface of the hemoglobin molecule (HbS). Under deoxygenated conditions, these patches cause HbS molecules to polymerize into long fibers, distorting the RBC into a sickle shape. **2. Analysis of Incorrect Options:** * **Option A:** This is a common distractor. It reverses the order. In HbS, Glutamic acid is the *original* amino acid being replaced, not the replacement itself. * **Option C:** Histidine and Valine at position 8 are not involved in the primary pathology of Sickle Cell Anemia. * **Option D:** The mutation in Sickle Cell Anemia occurs exclusively in the **$\beta$-globin chain**, not the $\alpha$-chain. **3. NEET-PG High-Yield Clinical Pearls:** * **Genetics:** It is an autosomal recessive disorder. The mutation is a **missense mutation**. * **Electrophoresis:** On alkaline electrophoresis, HbS moves **slower** toward the anode than HbA because it has lost two negative charges (one per $\beta$-chain). * **Protective Effect:** Heterozygotes (Sickle cell trait) show resistance to *Plasmodium falciparum* malaria. * **Diagnosis:** The "Gold Standard" for diagnosis is **Hb Electrophoresis** or **HPLC**. Screening is done via the Solubility test or Sodium Metabisulfite test.

Q: Which of the following is an autosomal dominant metabolic disorder?

Familial hypercholesterolemia. **Explanation:** The correct answer is **Familial Hypercholesterolemia (FH)**. **1. Why Familial Hypercholesterolemia is correct:** Most metabolic disorders (enzymopathies) follow an autosomal recessive (AR) inheritance pattern because a 50% reduction in enzyme activity in heterozygotes is usually sufficient for normal function. However, **Familial Hypercholesterolemia** is a notable exception. It is an **Autosomal Dominant (AD)** disorder caused by mutations in the **LDL receptor gene**. This leads to a "dosage effect" where even a 50% reduction in functional receptors (heterozygotes) causes significant elevation in plasma LDL, leading to premature atherosclerosis and xanthomas. **2. Why other options are incorrect:** * **Cystic Fibrosis:** This is the most common lethal **Autosomal Recessive** disorder in Caucasians, caused by a mutation in the CFTR gene on Chromosome 7. * **Phenylketonuria (PKU):** This is a classic **Autosomal Recessive** metabolic disorder caused by a deficiency of Phenylalanine Hydroxylase. * **Alpha-1-antitrypsin deficiency:** This follows an **Autosomal Recessive** (specifically co-dominant) inheritance pattern, leading to emphysema and liver cirrhosis. **3. NEET-PG Clinical Pearls:** * **Mnemonic for AD Metabolic Disorders:** Most AD disorders are structural (e.g., Marfan) or regulatory. Metabolic exceptions include **FH**, **Acute Intermittent Porphyria (AIP)**, and **Hereditary Spherocytosis**. * **FH Clinical Markers:** Look for **Tendon Xanthomas** (especially Achilles) and **Corneal Arcus** in a young patient with a family history of early Myocardial Infarction. * **Genetics:** Homozygous FH is much more severe, often presenting with MI before age 20.

Q: Which of the following diseases has an autosomal recessive inheritance pattern?

Cystic fibrosis. **Explanation:** **Cystic Fibrosis (Option A)** is the correct answer. It is one of the most common **autosomal recessive** disorders, particularly in Caucasian populations. It is caused by a mutation in the **CFTR gene** located on **chromosome 7**. This mutation leads to defective chloride ion transport across epithelial membranes, resulting in thick, dehydrated secretions in the lungs, pancreas, and reproductive tract. **Analysis of Incorrect Options:** * **Hydrocephalus (Option B):** This is a clinical sign (excess CSF accumulation) rather than a single genetic disease. While it can be part of genetic syndromes, the most common inherited form (X-linked aqueductal stenosis) follows an **X-linked recessive** pattern. Most cases are sporadic or acquired (e.g., post-meningitic). * **Duchenne Muscular Dystrophy (Option C):** This is a classic example of an **X-linked recessive** disorder. It involves a mutation in the *Dystrophin* gene (the largest known human gene), primarily affecting males. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for Autosomal Recessive (AR) Disorders:** "ABCDE PQRST" – **A**lbinism, **B**artter syndrome, **C**ystic fibrosis/CAH, **D**eafness (sensorineural), **E**nzyme deficiencies (most), **P**KU, **Q**-fever (not genetic, but used for flow), **R**enal tubular acidosis, **S**ickle cell anemia/Thalassemia, **T**ay-Sachs. * **CFTR Mutation:** The most common mutation is **ΔF508** (deletion of phenylalanine at position 508). * **Diagnostic Gold Standard:** Sweat Chloride Test (Chloride levels >60 mmol/L). * **Associated Finding:** Congenital Bilateral Absence of the Vas Deferens (CBAVD) leading to infertility in males.

Question 1

The molecule, which is the initiator of cataract formation in the eye lens and whose 1-phosphate derivative is responsible for liver failure, is:

Accepted Answer

Galacticol

Answer

Sorbitol

Answer

Mannitol

Answer

Inositol

Question 2

What conditions may develop in a child born to a mother with phenylketonuria?

Accepted Answer

Microcephaly, mental retardation, congenital heart disease

Answer

Mental retardation, cataract, congenital heart disease

Answer

Hydrocephalus, cataract

Answer

Microcephaly, cataract, renal dysplasia

Question 3

In Wilson disease, which element is chelated?

Accepted Answer

Zinc

Answer

Iron

Answer

Copper

Answer

Selenium

Question 4

What is the cause of alpha thalassemia?

Accepted Answer

Deletion of alpha genes

Answer

Deletion of beta genes

Answer

Excess of alpha genes

Answer

Single amino acid substitution in alpha chain

Question 5

In sickle cell anemia, what is the amino acid replacement at the beta-globin chain?

Accepted Answer

Glutamic acid by Valine in beta-6

Answer

Valine by Glutamic acid in beta-6

Answer

Histidine and Valine in beta-8

Answer

Amino acid at alpha-6

Question 6

Which of the following is an autosomal dominant metabolic disorder?

Accepted Answer

Familial hypercholesterolemia

Answer

Cystic fibrosis

Answer

Phenylketonuria

Answer

Alpha-1-antitrypsin deficiency

Question 7

Which of the following diseases has an autosomal recessive inheritance pattern?

Accepted Answer

Cystic fibrosis

Answer

Hydrocephalus

Answer

Duchene muscular dystrophy

Answer

None of the above

Question 8

Adrenogenital syndrome is most commonly caused by which of the following?

Accepted Answer

21-hydroxylase deficiency

Answer

17-alpha-hydroxylase deficiency

Answer

3-beta-hydroxylase deficiency

Answer

Steroid sulfatase deficiency

Question 9

Patients with G6PD deficiency often have an increased susceptibility to infection, which in turn may precipitate a hemolytic episode. What is the most likely underlying mechanism for the increased risk of infection?

Accepted Answer

Decreased amount of reduced nicotinamide adenine dinucleotide phosphate (NADPH) in the white blood cells

Answer

Decreased amount of glutathione in the white blood cells

Answer

Defective phagocytosis

Answer

Deficiency of myeloperoxidase

Question 10

A patient is on treatment for his abnormal lipid profile blood tests. All of the following statements are true about familial hypercholesterolemia, except?

Accepted Answer

Patients with receptor-defective LDL receptor defects have the worst prognosis.

Answer

Cutaneous xanthomas on the hands, wrists, elbows present.

Answer

Total cholesterol levels can be higher than 1000 mg/dL.

Answer

Accelerated atherosclerosis is a devastating complication.

Genetic Disorders and Biochemical Pathology — MCQs

Genetic Disorders and Biochemical Pathology — MCQs

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