Biochemical Markers for Disease Diagnosis Indian Medical PG Practice Questions and MCQs
Practice Indian Medical PG questions for Biochemical Markers for Disease Diagnosis. These multiple choice questions (MCQs) cover important concepts and help you prepare for your exams.
Biochemical Markers for Disease Diagnosis Indian Medical PG Question 1: Preferred biochemical marker(s) in patients presenting with myocardial infarction:
- A. Cardiac specific Troponins (Correct Answer)
- B. All of the options
- C. Myoglobin
- D. CK-MB
Biochemical Markers for Disease Diagnosis Explanation: ***Cardiac specific Troponins***
- **Cardiac troponins** (cTnI and cTnT) are the preferred and most sensitive and specific biomarkers for diagnosing **myocardial infarction (MI)**.
- They are proteins released into the bloodstream when myocardial cells are damaged, and their levels rise within hours of MI onset and remain elevated for several days.
*All of the options*
- While other markers like **CK-MB** and **Myoglobin** were historically used, **cardiac troponins** have superior specificity and sensitivity for MI.
- The latest guidelines from major cardiology societies recommend troponins as the primary diagnostic markers.
*Myoglobin*
- **Myoglobin** is an early marker, but it is not specific to cardiac muscle and can be elevated in various conditions involving skeletal muscle damage.
- Its short half-life means it can return to normal quickly, making it less reliable for diagnosing MI, especially if there's a delay in presentation.
*CK-MB*
- **Creatine Kinase-MB (CK-MB)** is a more specific marker than total CK for cardiac muscle damage but is still less specific than cardiac troponins.
- It can be elevated in conditions like **myocarditis** or **pericarditis**, and its levels typically peak and decline earlier than troponins, limiting its diagnostic window.
Biochemical Markers for Disease Diagnosis Indian Medical PG Question 2: Which of the following reagents would be most useful in determining the N-terminal amino acid of a polypeptide?
- A. Trypsin
- B. Carboxypeptidase
- C. Phenylisothiocyanate (Correct Answer)
- D. Cyanogen bromide
Biochemical Markers for Disease Diagnosis Explanation: ***Phenylisothiocyanate***
- **Phenylisothiocyanate** (PITC), also known as Edman's reagent, is used in the **Edman degradation** method to identify the N-terminal amino acid.
- It sequentially cleaves the **N-terminal amino acid** without hydrolyzing the rest of the peptide chain, allowing for identification by chromatography.
*Trypsin*
- **Trypsin** is a protease that cleaves peptide bonds at the carboxyl side of **lysine** and **arginine** residues.
- It is used for peptide fragmentation, not for determining the N-terminal amino acid.
*Carboxypeptidase*
- **Carboxypeptidases** are exopeptidases that cleave amino acids from the **C-terminal end** of a polypeptide chain.
- They are used to identify the C-terminal amino acid, not the N-terminal.
*Cyanogen bromide*
- **Cyanogen bromide (CNBr)** is a chemical reagent that specifically cleaves peptide bonds on the C-terminal side of **methionine** residues.
- It is used for specific peptide fragmentation and not for N-terminal sequencing.
Biochemical Markers for Disease Diagnosis Indian Medical PG Question 3: Cardiac biomarker used for diagnosing reinfarction 8 days after initial ischemia is?
- A. Troponins
- B. CK-MB (Correct Answer)
- C. Myoglobin
- D. LDH
Biochemical Markers for Disease Diagnosis Explanation: ***CK-MB***
- **CK-MB** (creatine kinase-MB) levels typically return to normal within **2-3 days** after an initial myocardial infarction, making it a suitable marker for detecting reinfarction several days later because its re-elevation would indicate new damage [2].
- Its relatively rapid normalization kinetics compared to troponins allows for better discrimination of new cardiac injury following the resolution of a prior event [2].
*Troponins*
- **Cardiac troponins (I and T)** remain elevated for an extended period, typically **7-10 days** or even longer, after an acute myocardial infarction [3].
- Due to their prolonged elevation, troponins would likely still be elevated from the initial infarct 8 days prior, making it difficult to detect a reinfarction based solely on their levels [3].
*Myoglobin*
- **Myoglobin** is one of the earliest markers to rise after myocardial injury but also has a very rapid clearance, returning to baseline within **24 hours**.
- While sensitive for early detection, its short half-life makes it unsuitable for diagnosing reinfarction 8 days after initial ischemia, as any elevation would have resolved much earlier.
*LDH*
- **Lactate dehydrogenase (LDH)** is a late marker of myocardial infarction, rising within 24-48 hours and remaining elevated for up to **10-14 days** [1].
- Similar to troponins, the prolonged elevation of LDH from the initial infarct would obscure the detection of a reinfarction 8 days later [1].
Biochemical Markers for Disease Diagnosis Indian Medical PG Question 4: Biochemical etiology of Alzheimer's disease relates to:
- A. Dopamine
- B. Acetylcholine (Correct Answer)
- C. GABA
- D. Serotonin
Biochemical Markers for Disease Diagnosis Explanation: ***Acetylcholine***
- Alzheimer's disease is significantly associated with a **reduction in cholinergic neuronal activity** in the brain, impacting memory and learning.
- Medications for Alzheimer's disease often aim to **increase acetylcholine levels** or prevent its breakdown (e.g., cholinesterase inhibitors).
*Dopamine*
- **Dopamine deficits** are primarily associated with **Parkinson's disease**, affecting motor control and movement.
- While dopamine may play a minor role, it is **not considered the primary biochemical etiology** of Alzheimer's.
*GABA*
- **GABA (gamma-aminobutyric acid)** is the main inhibitory neurotransmitter in the brain and is often associated with anxiety disorders and epilepsy.
- While GABAergic system changes can occur in Alzheimer's, they are **secondary to the primary cholinergic dysfunction**.
*Serotonin*
- **Serotonin** is widely known for its role in mood, sleep, and appetite regulation, and its imbalances are linked to depression and anxiety.
- While some **serotonergic changes** can be observed in Alzheimer's disease, the primary biochemical deficit is not serotonin.
Biochemical Markers for Disease Diagnosis Indian Medical PG Question 5: Which of the following is not expressed in majority of cases of pediatric B-cell acute lymphoblastic leukemia?
- A. CD7 (Correct Answer)
- B. Terminal deoxynucleotidyl transferase (TdT)
- C. CD19
- D. CD10
Biochemical Markers for Disease Diagnosis Explanation: ***CD7***
- **CD7** is a **T-cell associated antigen** and is typically **not expressed** on B-cell acute lymphoblastic leukemia (ALL) cells [1].
- Its presence would suggest a **T-cell ALL** or an atypical mixed phenotype leukemia, rather than a B-cell ALL.
*Terminal deoxynucleotidyl transferase (TdT)*
- **TdT** is a **nuclear enzyme** that adds random nucleotides to V(D)J gene segments during lymphoid development and is a **marker of immaturity** in both B and T cell lymphoblasts [2].
- It is **expressed in the majority of B-cell ALL cases** and is crucial for diagnosis.
*CD19*
- **CD19** is an **early and pan-B-cell marker** that is consistently expressed by B-cell lymphoblasts throughout their development [1].
- It is a **key diagnostic marker** for B-cell ALL.
*CD10*
- **CD10**, also known as **common acute lymphoblastic leukemia antigen (CALLA)**, is expressed in most progenitor and pre-B ALLs [1].
- Its presence is an important marker used in the immunophenotyping of **B-cell ALL**, particularly the common ALL subtype [2].
**References:**
[1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of White Blood Cells, Lymph Nodes, Spleen, and Thymus, p. 598.
[2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of White Blood Cells, Lymph Nodes, Spleen, and Thymus, pp. 599-600.
Biochemical Markers for Disease Diagnosis Indian Medical PG Question 6: Which of the following statements about the inheritance of an X-linked recessive trait is true?
- A. Fathers can transmit X-linked traits to their sons
- B. 25% of sons of a carrier mother are affected
- C. Carrier mothers have a 50% chance of transmitting the disease to their sons (Correct Answer)
- D. 100% of daughters of a diseased father are affected
Biochemical Markers for Disease Diagnosis Explanation: ***Carrier mothers have a 50% chance of transmitting the disease to their sons***
- A mother who is a carrier for an **X-linked recessive trait** has one normal X chromosome and one X chromosome carrying the recessive allele.
- Each son she has has a **50% chance** of inheriting the X chromosome with the recessive allele (and thus being affected) and a 50% chance of inheriting the normal X chromosome.
*Fathers can transmit X-linked traits to their sons*
- Fathers transmit their **Y chromosome** to their sons, not an X chromosome.
- Therefore, fathers cannot directly transmit X-linked traits to their sons.
*25% of sons of a carrier mother are affected*
- This statement is incorrect; as explained above, a carrier mother has a **50% chance** of transmitting the affected X chromosome to each son.
- The 25% probability typically applies to autosomal recessive inheritance, not X-linked.
*100% of daughters of a diseased father are affected*
- A diseased father (meaning he has the **X-linked recessive trait**) will pass his single X chromosome to all of his daughters.
- Therefore, all his daughters will be **obligate carriers**, but they will only be affected if their mother also contributes an X chromosome with the recessive allele (which is rare for recessive traits).
Biochemical Markers for Disease Diagnosis Indian Medical PG Question 7: Which of the following is a sex-linked disorder?
- A. Hemophilia (Correct Answer)
- B. Neurofibromatosis
- C. Klinefelter's syndrome
- D. Thalassemia
Biochemical Markers for Disease Diagnosis Explanation: ***Hemophilia***
- Hemophilia is an **X-linked recessive disorder**, meaning the gene responsible is located on the X chromosome.
- Males are predominantly affected because they have only one X chromosome, so a single copy of the mutated gene is sufficient to cause the disease.
*Neurofibromatosis*
- Neurofibromatosis is an **autosomal dominant disorder**, meaning a single copy of the mutated gene on a non-sex chromosome is enough to cause the condition.
- It affects males and females equally and is characterized by tumors along nerves and skin changes.
*Klinefelter's syndrome*
- Klinefelter's syndrome is a **chromosomal disorder** resulting from an extra X chromosome in males (XXY), not a single gene mutation on a sex chromosome.
- While it involves sex chromosomes, it's categorized as a **sex chromosome aneuploidy** rather than a sex-linked disorder in the traditional genetic sense.
*Thalassemia*
- Thalassemia is an **autosomal recessive disorder**, meaning it requires two copies of the mutated gene (one from each parent) on non-sex chromosomes to manifest.
- It affects the production of hemoglobin and impacts males and females equally.
Biochemical Markers for Disease Diagnosis Indian Medical PG Question 8: A patient presents with ochronosis. Which of the following substance accumulates in this condition?
- A. Homogentisic acid (Correct Answer)
- B. Phenylalanine
- C. Tyrosine
- D. Tryptophan
Biochemical Markers for Disease Diagnosis Explanation: ***Homogentisic acid***
- Ochronosis (alkaptonuria) is caused by the accumulation of **homogentisic acid** in connective tissues, leading to a dark blue-black discoloration of cartilage, skin, and organs.
- This accumulation results from a deficiency of **homogentisate 1,2-dioxygenase**, an enzyme involved in the metabolism of **tyrosine**.
- The accumulated homogentisic acid polymerizes and deposits in tissues, causing the characteristic pigmentation.
*Phenylalanine*
- Accumulation of **phenylalanine** occurs in **phenylketonuria (PKU)**, not ochronosis.
- PKU is caused by deficiency of phenylalanine hydroxylase and presents with intellectual disability, musty odor, and fair complexion if untreated.
*Tyrosine*
- While ochronosis involves a defect in **tyrosine metabolism**, tyrosine itself does not accumulate in this condition.
- Tyrosine accumulation occurs in **tyrosinemia**, which presents with different clinical features including hepatic dysfunction and renal tubular defects.
*Tryptophan*
- Defects in **tryptophan metabolism** are associated with conditions like **Hartnup disease**, which presents with pellagra-like symptoms, not ochronosis.
- Tryptophan is a precursor for **serotonin** and **niacin (vitamin B3)**.
Biochemical Markers for Disease Diagnosis Indian Medical PG Question 9: A patient reports a change in colour of urine on air exposure. All are true about the condition shown below except:
- A. Blackening of urine is accelerated on exposure to sunlight
- B. Alkaptone bodies are deposited in intervertebral disc
- C. Urine Benedict's test is negative (Correct Answer)
- D. The condition is caused by deficiency of homogentisate 1,2-dioxygenase
Biochemical Markers for Disease Diagnosis Explanation: ***Urine Benedict's test is negative***
- This is FALSE - Benedict's test is actually **POSITIVE** in alkaptonuria because **homogentisic acid** is a reducing agent.
- Homogentisic acid readily **reduces Benedict's reagent**, giving a positive test result in alkaptonuria patients.
*Blackening of urine is accelerated on exposure to sunlight*
- This is TRUE - **UV light** and sunlight accelerate the **oxidation of homogentisic acid** in urine.
- The characteristic **dark discoloration** occurs more rapidly when exposed to light and air.
*Alkaptone bodies are deposited in intervertebral disc*
- This is TRUE - **Homogentisic acid (alkaptone bodies)** polymerizes to form **ochronotic pigment** deposits.
- These deposits accumulate in **cartilage** including intervertebral discs, causing degenerative changes and spondylosis.
*The condition is caused by deficiency of homogentisate 1,2-dioxygenase*
- This is TRUE - Alkaptonuria is caused by deficiency of **homogentisate 1,2-dioxygenase** enzyme in the **tyrosine metabolic pathway**.
- This enzyme deficiency leads to accumulation of **homogentisic acid** in blood and urine, causing the characteristic symptoms.
Biochemical Markers for Disease Diagnosis Indian Medical PG Question 10: All are involved in bilirubin metabolism except?
- A. Biliverdin reductase
- B. Heme oxygenase
- C. Glucuronyl transferase
- D. ALA synthase (Correct Answer)
Biochemical Markers for Disease Diagnosis Explanation: ***ALA synthase***
- **ALA synthase** is the enzyme responsible for the first committed step in **heme synthesis**, not bilirubin metabolism.
- It catalyzes the condensation of **succinyl CoA** and **glycine** to form δ-aminolevulinic acid (ALA).
*Biliverdin reductase*
- This enzyme catalyzes the conversion of **biliverdin**, a green pigment, into **unconjugated bilirubin**, a yellow pigment.
- It is an essential step in the breakdown pathway of **heme** into bilirubin.
*Heme oxygenase*
- **Heme oxygenase** is the enzyme that cleaves the **heme ring** to form **biliverdin**, releasing carbon monoxide and iron.
- This is the initial and rate-limiting step in **heme catabolism**, leading to bilirubin formation.
*Glucuronyl transferase*
- **UDP-glucuronyl transferase** (UGT) conjugates unconjugated bilirubin with **glucuronic acid** in the liver.
- This conjugation process makes bilirubin water-soluble, allowing its excretion into the **bile**.
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