Biochemical Markers for Disease Diagnosis — MCQs
Preferred biochemical marker(s) in patients presenting with myocardial infarction:
Which of the following reagents would be most useful in determining the N-terminal amino acid of a polypeptide?
Cardiac biomarker used for diagnosing reinfarction 8 days after initial ischemia is?
Biochemical etiology of Alzheimer's disease relates to:
Which of the following is not expressed in majority of cases of pediatric B-cell acute lymphoblastic leukemia?
Which of the following statements about the inheritance of an X-linked recessive trait is true?
Which of the following is a sex-linked disorder?
A patient presents with ochronosis. Which of the following substance accumulates in this condition?
A patient reports a change in colour of urine on air exposure. All are true about the condition shown below except:
All are involved in bilirubin metabolism except?
Biochemical Markers for Disease Diagnosis Indian Medical PG Practice Questions and MCQs
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
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.
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
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.
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
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].
Question 4: Biochemical etiology of Alzheimer's disease relates to:
- A. Dopamine
- B. Acetylcholine (Correct Answer)
- C. GABA
- D. Serotonin
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.
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
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.
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
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).
Question 7: Which of the following is a sex-linked disorder?
- A. Hemophilia (Correct Answer)
- B. Neurofibromatosis
- C. Klinefelter's syndrome
- D. Thalassemia
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.
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
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)**.
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
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.
Question 10: All are involved in bilirubin metabolism except?
- A. Biliverdin reductase
- B. Heme oxygenase
- C. Glucuronyl transferase
- D. ALA synthase (Correct Answer)
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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