Genetic Disorders and Biochemical Pathology Practice Questions

Q: Enzyme imiglucerase (Cerezyme) is used in the treatment of which condition?

Gaucher's disease. **Explanation:** **Imiglucerase (Cerezyme)** is a recombinant form of the human lysosomal enzyme **beta-glucocerebrosidase**. It is the mainstay of **Enzyme Replacement Therapy (ERT)** for **Gaucher’s disease**, the most common lysosomal storage disorder. 1. **Why Gaucher’s Disease is Correct:** Gaucher’s disease is caused by a deficiency of the enzyme glucocerebrosidase, leading to the accumulation of glucosylceramide (glucocerebroside) in macrophages. These "Gaucher cells" infiltrate the bone marrow, liver, and spleen. Imiglucerase replaces the deficient enzyme, reducing organomegaly and improving hematological parameters. 2. **Why Other Options are Incorrect:** * **Galactosemia:** This is a metabolic disorder of carbohydrate metabolism (deficiency of GALT, GALK, or GALE). Treatment is dietary restriction of galactose/lactose, not ERT. * **Niemann-Pick Disease:** This is caused by a deficiency of **sphingomyelinase** (Types A and B). While ERT (Olipudase alfa) exists for Type B, Imiglucerase is specific only to the glucocerebrosidase deficiency in Gaucher’s. * **Trans-maxillary approach:** This is a surgical technique (often used for skull base tumors), not a biochemical condition or a target for pharmacological therapy. **High-Yield Clinical Pearls for NEET-PG:** * **Gaucher Cells:** Described as having a **"wrinkled paper"** or "crumpled silk" cytoplasm. * **Clinical Triad:** Hepatosplenomegaly, bone pain/crises (Erlenmeyer flask deformity of femur), and cytopenias. * **Biochemical Marker:** Elevated levels of **Chitotriosidase** are used to monitor disease activity and response to ERT. * **Alternative Treatment:** **Miglustat** or **Eliglustat** (Substrate Reduction Therapy) can be used for patients who cannot tolerate ERT.

Q: In all the following metabolic disorders, clinical features are seen due to accumulation of toxic compounds EXCEPT?

Mitochondrial disorders. ### Explanation The fundamental distinction in metabolic pathology lies between **"Intoxication-type"** disorders and **"Energy-deficiency"** disorders. **1. Why Mitochondrial Disorders is the Correct Answer:** Mitochondrial disorders (e.g., MELAS, Leigh syndrome) primarily result from a **failure in energy production (ATP)** rather than the accumulation of a specific upstream toxic metabolite. The clinical features—such as encephalopathy, myopathy, and lactic acidosis—arise because tissues with high metabolic demands (brain, muscle, heart) cannot meet their energy requirements due to defects in the respiratory chain or oxidative phosphorylation. **2. Why the Other Options are Incorrect:** * **Phenylketonuria (PKU):** Caused by a deficiency of phenylalanine hydroxylase. Clinical features (intellectual disability, musty odor) are due to the **toxic accumulation of phenylalanine** and its metabolites (phenylpyruvate). * **Maple Syrup Urine Disease (MSUD):** Caused by a defect in the Branched-Chain Alpha-Keto Acid Dehydrogenase complex. Symptoms (seizures, encephalopathy) are due to the **toxic buildup of Leucine, Isoleucine, and Valine.** * **Urea Cycle Defects:** Defects in enzymes like Ornithine Transcarbamylase (OTC) lead to the **toxic accumulation of Ammonia**, which is highly neurotoxic and causes cerebral edema. ### NEET-PG High-Yield Pearls: * **Intoxication Disorders:** Characterized by a "symptom-free interval" after birth followed by acute crisis (vomiting, coma) triggered by protein intake. (Includes: Organic acidemias, Urea cycle defects, Galactosemia). * **Energy Deficiency Disorders:** Often present with hypoglycemia, hypotonia, and cardiomyopathy. (Includes: Mitochondrial disorders, Fatty acid oxidation defects, Glycogen storage diseases). * **Mnemonic:** In **M**itochondrial diseases, the **M**achinery (ATP production) is broken; in others, the **P**ipe is clogged (Toxic buildup).

Q: What is the most common chromosomal defect?

Down syndrome. **Explanation:** **Down Syndrome (Trisomy 21)** is the most common chromosomal abnormality among live-born infants. It occurs due to the presence of an extra copy of chromosome 21, most frequently resulting from **meiotic non-disjunction** (95% of cases), which is strongly associated with advanced maternal age. Its prevalence is approximately 1 in 700 to 800 live births, making it significantly more frequent than other autosomal or sex chromosome aneuploidies. **Analysis of Incorrect Options:** * **Turner Syndrome (45, XO):** This is the most common sex chromosome abnormality in females, but its incidence (1 in 2,500 live births) is much lower than Down syndrome. Notably, it is the most common cause of spontaneous abortion due to chromosomal defects. * **Edwards Syndrome (Trisomy 18):** This is the second most common autosomal trisomy. However, it is much rarer (1 in 5,000–8,000 births) and has a very high mortality rate in utero and infancy. * **Patau Syndrome (Trisomy 13):** This is the least common of the three viable autosomal trisomies (1 in 10,000–16,000 births) and presents with the most severe clinical phenotype, including midline defects like holoprosencephaly. **High-Yield Clinical Pearls for NEET-PG:** * **Most common cause:** Meiotic non-disjunction (maternal origin). * **Second most common cause:** Robertsonian translocation (usually involving chromosomes 14 and 21). * **Screening:** First-trimester screening shows **increased nuchal translucency**, **decreased PAPP-A**, and **increased β-hCG**. * **Quadruple Test (Second Trimester):** Characterized by **low AFP**, **low Estriol**, **high hCG**, and **high Inhibin A**.

Q: Which of the following is NOT an X-linked disease?

Wilson's disease. **Explanation:** The correct answer is **Wilson’s disease** because it follows an **Autosomal Recessive** inheritance pattern, not X-linked. **1. Why Wilson’s Disease is the correct answer:** Wilson’s disease is caused by mutations in the **ATP7B gene** located on **Chromosome 13**. This defect leads to impaired biliary copper excretion and failure to incorporate copper into ceruloplasmin, resulting in toxic copper accumulation in the liver, brain (basal ganglia), and cornea (Kayser-Fleischer rings). Since the gene is on an autosome, it affects males and females equally. **2. Why the other options are incorrect:** * **Androgen Insensitivity Syndrome (AIS):** This is an **X-linked recessive** condition caused by mutations in the androgen receptor gene on the X chromosome. Affected individuals are genotypically male (46, XY) but phenotypically female. * **Duchenne Muscular Dystrophy (DMD):** This is a classic **X-linked recessive** disorder caused by a mutation in the *Dystrophin* gene (the largest known human gene), located on the X chromosome. * **Hemophilia:** Both Hemophilia A (Factor VIII deficiency) and Hemophilia B (Factor IX deficiency) are inherited in an **X-linked recessive** manner. **High-Yield Clinical Pearls for NEET-PG:** * **Wilson vs. Menkes:** While Wilson’s is Autosomal Recessive (ATP7B), **Menkes disease** (kinky hair syndrome) is **X-linked Recessive** (ATP7A). * **Common X-linked Recessive Mnemonic:** "**G**o **C**herish **H**is **D**iamonds" (**G**6PD deficiency, **C**olor blindness, **H**emophilia/Hunter syndrome, **D**MD). * **Wilson’s Diagnosis:** Look for low serum ceruloplasmin, increased urinary copper, and the "Giant Panda" sign on brain MRI.

Q: For which glycogen storage disease, enzyme replacement therapy is available?

Glycogen storage disease type II. **Explanation:** **Glycogen Storage Disease Type II (Pompe Disease)** is the correct answer because it is the only GSD that is also classified as a **lysosomal storage disorder**. It is caused by a deficiency of **Acid α-1,4-glucosidase (Acid Maltase)**, the enzyme responsible for breaking down glycogen within lysosomes. Since the pathology involves a single lysosomal enzyme deficiency, it is amenable to **Enzyme Replacement Therapy (ERT)**. The FDA-approved recombinant human enzyme **Alglucosidase alfa** (and newer generations like Avalglucosidase alfa) is used to improve cardiac and skeletal muscle function in these patients. **Analysis of Incorrect Options:** * **GSD Type I (von Gierke Disease):** Caused by Glucose-6-Phosphatase deficiency. It is a metabolic pathway defect in the cytosol/ER of hepatocytes. Management focuses on dietary prevention of hypoglycemia (e.g., uncooked cornstarch). * **GSD Type III (Cori Disease):** Caused by Debranching enzyme deficiency. Management is primarily nutritional (high protein, frequent meals). * **GSD Type IV (Andersen Disease):** Caused by Branching enzyme deficiency, leading to the accumulation of abnormal glycogen (amylopectin-like). Treatment is supportive, often requiring liver transplantation. **High-Yield Clinical Pearls for NEET-PG:** * **Pompe is Unique:** It is the only GSD with **normal blood glucose levels** (no hypoglycemia) because cytosolic glycogenolysis remains intact. * **Clinical Triad:** Cardiomegaly (massive), hypotonia ("floppy baby"), and early death from heart failure. * **Histology:** PAS-positive material in lysosomes. * **Mnemonic:** "Pompe trashes the **Pump** (heart)."

Q: An albino girl is married to a normal boy. What are the chances of their having an affected child and what are the chances of their children being carriers?

None affected, all carriers. ### Explanation **1. Understanding the Correct Answer (Option A)** Albinism (specifically Oculocutaneous Albinism) is a classic **Autosomal Recessive (AR)** disorder. For an individual to be affected, they must possess two mutant alleles (genotype **aa**). A "normal" individual, unless specified as a carrier, is assumed to be homozygous dominant (genotype **AA**) in medical genetics problems. * **The Cross:** Mother (aa) x Father (AA) * **Punnett Square:** All offspring will have the genotype **Aa**. * **Phenotype:** Since they possess one dominant allele (A), none will manifest the disease (None affected). * **Genotype:** Since they all carry one recessive allele (a), 100% will be obligate heterozygotes (All carriers). **2. Analysis of Incorrect Options** * **Option B (All normal):** While phenotypically true, it is incomplete as it ignores the carrier status, which is a critical genetic implication. * **Option C (50% carriers):** This would only occur if the father was a carrier (Aa) and the mother was homozygous normal (AA). * **Option D (50% affected, 50% carriers):** This is the result of a **Test Cross** (aa x Aa). It only occurs if the "normal" father was actually a carrier (pseudodominance). **3. NEET-PG Clinical Pearls** * **Biochemical Defect:** Most commonly due to a deficiency of the enzyme **Tyrosinase**, which converts Tyrosine to DOPA and Melanin. * **Inheritance Pattern:** Always assume Autosomal Recessive for Albinism unless Ocular Albinism (X-linked) is specifically mentioned. * **Key Association:** Albinism is a feature of **Chédiak-Higashi syndrome** (look for giant cytoplasmic granules in neutrophils and recurrent infections). * **Risk Calculation:** In AR disorders, if both parents are carriers (Aa x Aa), the risk of an affected child is 25%, and the risk of a healthy child being a carrier is 2/3 (66%).

Q: The hallmarks of type Ia glycogen storage disease are all of the following except?

Metabolic alkalosis. **Explanation:** **Type Ia Glycogen Storage Disease (Von Gierke Disease)** is caused by a deficiency of **Glucose-6-Phosphatase**, the enzyme responsible for converting Glucose-6-Phosphate into free glucose. This enzyme is crucial for both glycogenolysis and gluconeogenesis. **Why Metabolic Alkalosis is the correct answer:** In Von Gierke disease, the inability to produce glucose leads to the shunting of Glucose-6-Phosphate into the glycolytic pathway, resulting in excessive production of pyruvate and subsequently **lactic acid**. This leads to **Metabolic Acidosis** (specifically a high anion gap metabolic acidosis), not metabolic alkalosis. **Why the other options are incorrect (Hallmarks of GSD Ia):** * **Hypoglycemia (A):** Severe fasting hypoglycemia occurs because the liver cannot release free glucose into the blood from glycogen stores or via gluconeogenesis. * **Hyperuricemia (C):** Increased G-6-P levels divert into the Pentose Phosphate Pathway, increasing ribose-5-phosphate and purine synthesis. Additionally, lactic acid competes with uric acid for excretion in the kidneys, leading to gouty arthritis. * **Hyperlipidemia (D):** Low insulin and high glucagon levels trigger lipolysis. The liver also increases VLDL synthesis from excess acetyl-CoA, leading to hypertriglyceridemia and "doll-like" facies. **Clinical Pearls for NEET-PG:** * **Key Enzyme:** Glucose-6-Phosphatase (Type Ia); G-6-P Translocase (Type Ib). * **Type Ib specific:** Presents with the same features plus **neutropenia** and recurrent infections. * **Diagnostic Clue:** Hepatomegaly (due to glycogen and fat accumulation) with **no** splenomegaly. * **Treatment:** Frequent oral cornstarch (slow-release glucose) and avoidance of fructose/galactose.

Question 1

Accumulation of sphingomyelin in the spleen and liver is found in which condition?

Accepted Answer

Niemann-Pick disease

Answer

Gaucher's disease

Answer

Obstructive jaundice

Answer

Von Gierke's disease

Question 2

Enzyme imiglucerase (Cerezyme) is used in the treatment of which condition?

Accepted Answer

Gaucher's disease

Answer

Galactosemia

Answer

Niemann Pick disease

Answer

Trans-maxillary approach

Question 3

In all the following metabolic disorders, clinical features are seen due to accumulation of toxic compounds EXCEPT?

Accepted Answer

Mitochondrial disorders

Answer

Phenylketonuria

Answer

Maple syrup urine disease

Answer

Urea cycle defects

Question 4

What is the most common chromosomal defect?

Accepted Answer

Down syndrome

Answer

Turner syndrome

Answer

Edwards syndrome

Answer

Patau syndrome

Question 5

Which of the following is NOT an X-linked disease?

Accepted Answer

Wilson's disease

Answer

Androgen insensitivity syndrome

Answer

Duchenne muscular dystrophy

Answer

Hemophilia

Question 6

A genetic disorder appears in three consecutive generations of a family without any sex predilection. Phenotypically normal family members have healthy offspring. What is the pattern of inheritance of this disorder?

Accepted Answer

Autosomal dominant

Answer

Autosomal recessive

Answer

Mitochondrial inheritance

Answer

Uniparental disomy

Question 7

For which glycogen storage disease, enzyme replacement therapy is available?

Accepted Answer

Glycogen storage disease type II

Answer

Glycogen storage disease type I

Answer

Glycogen storage disease type III

Answer

Glycogen storage disease type IV

Question 8

A 29-year-old man has had angina for the past year with a family history of cardiovascular disease. His blood pressure is 120/80 mm Hg, total serum cholesterol is 185 mg/dL, and glucose is 85 mg/dL. A mutation involving a gene encoding for which of the following is most likely present in this man's family?

Accepted Answer

Apolipoprotein

Answer

Angiotensin

Answer

Endothelin

Answer

Factor VIII

Question 9

An albino girl is married to a normal boy. What are the chances of their having an affected child and what are the chances of their children being carriers?

Accepted Answer

None affected, all carriers

Answer

All normal

Answer

50% carriers

Answer

50% affected, 50% carriers

Question 10

The hallmarks of type Ia glycogen storage disease are all of the following except?

Accepted Answer

Metabolic alkalosis

Answer

Hypoglycemia

Answer

Hyperuricemia

Answer

Hyperlipidemia

Genetic Disorders and Biochemical Pathology — MCQs

Genetic Disorders and Biochemical Pathology — MCQs

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