Molecular Pathology — MCQs
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Which banding technique is most commonly used for karyotyping?
Which of the following is a channelopathy?
What is the genotype of Klinefelter syndrome?
The expression of which gene is most strongly associated with a high incidence of medullary carcinomas of the thyroid?
Molecular Pathology Indian Medical PG Practice Questions and MCQs
Question 251: Which banding technique is most commonly used for karyotyping?
- A. G banding (Correct Answer)
- B. Q banding
- C. C banding
- D. R banding
Explanation: ***G banding*** - This method is the **most widely used** technique for karyotyping, allowing clear visualization of chromosome bands under light microscopy [1][2]. - G banding helps in identifying **chromosomal abnormalities** and is routinely utilized in clinical genetics [2]. *C banding* - Primarily highlights the **centromeric regions** of chromosomes, but is less common than G banding for overall karyotyping. - Does not provide a full **karyotype view**, making it less suitable for routine analysis. *R banding* - Useful for providing **reverse staining**, which shows the bands in a different manner but is not as commonly employed in clinical settings. - Typically used to analyze specific **chromosomal translocations**, rather than routine karyotyping. *Q banding* - This technique involves **fluorescent microscopy** to visualize chromosomes but is not as prevalent for basic karyotyping. - Mainly used for detecting **specific chromosomal anomalies**, not the standard karyotype assessment. **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. (Basic Pathology) introduces the student to key general principles of pathology, both as a medical science and as a clinical activity with a vital role in patient care. Part 2 (Disease Mechanisms) provides fundamental knowledge about the cellular and molecular processes involved in diseases, providing the rationale for their treatment. Part 3 (Systematic Pathology) deals in detail with specific diseases, with emphasis on the clinically important aspects., pp. 54-55. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Genetic Disorders, pp. 167-168.
Question 252: Which of the following is a channelopathy?
- A. Anderson Tawil Syndrome (Correct Answer)
- B. Ataxia Telangiectasia
- C. Spinocerebellar Ataxia
- D. Friedreich Ataxia
Explanation: ***Anderson Tawil Syndrome*** - This syndrome is a **channelopathy** specifically linked to mutations in the **KCNJ2 gene**, which encodes a subunit of a potassium channel. [1] - It presents with a triad of symptoms: **paroxysmal periodic paralysis**, **cardiac arrhythmias (long QT syndrome)**, and **dysmorphic facial features**. *Ataxia Telangiectasia* - This is an **autosomal recessive disorder** characterized by **progressive cerebellar ataxia**, oculocutaneous telangiectasias, and immunodeficiency. - It is caused by mutations in the **ATM gene**, which is involved in DNA repair, not ion channel function. *Spinocerebellar Ataxia* - This is a broad group of **hereditary ataxias** primarily affecting the cerebellum and spinal cord. - Most forms involve **trinucleotide repeat expansions** or other gene mutations that lead to neuronal degeneration, not directly affecting ion channels. *Friedreich Ataxia* - This is an **autosomal recessive neurodegenerative disorder** caused by a **GAA triplet repeat expansion** in the **FXN gene**, which encodes the protein frataxin. - The disease involves **progressive ataxia**, dysarthria, and loss of proprioception, but it is not classified as a channelopathy. **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. (Basic Pathology) introduces the student to key general principles of pathology, both as a medical science and as a clinical activity with a vital role in patient care. Part 2 (Disease Mechanisms) provides fundamental knowledge about the cellular and molecular processes involved in diseases, providing the rationale for their treatment. Part 3 (Systematic Pathology) deals in detail with specific diseases, with emphasis on the clinically important aspects., pp. 120-122.
Question 253: What is the genotype of Klinefelter syndrome?
- A. 47,XXY (Correct Answer)
- B. Trisomy 13
- C. 47,XXX
- D. 45,X
Explanation: ***47,XXY*** - This genotype represents the presence of an **extra X chromosome** in males, which is the defining characteristic of Klinefelter syndrome. - Individuals with this syndrome typically have **47 chromosomes** instead of the usual 46. *45,X* - This genotype describes **Turner syndrome**, which is characterized by the absence of one X chromosome in females [1]. - Individuals with Turner syndrome are typically female and present with a distinct set of physical features and health issues. *47,XXX* - This genotype is known as **Triple X syndrome** or **Trisomy X**, which affects females who have an extra X chromosome. - While it involves an extra sex chromosome, it is distinct from Klinefelter syndrome both in terms of affected sex and clinical presentation. *Trisomy 13* - This refers to **Patau syndrome**, a severe chromosomal disorder caused by an extra copy of chromosome 13. - It is an **autosomal trisomy** and is not related to sex chromosome abnormalities like Klinefelter syndrome. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Genetic Disorders, pp. 191-192.
Question 254: The expression of which gene is most strongly associated with a high incidence of medullary carcinomas of the thyroid?
- A. p53
- B. Ret proto-oncogene (Correct Answer)
- C. Rb gene
- D. Her2/neu
Explanation: ***Ret proto-oncogene (Correct Answer)*** - **Mutations** in the **RET proto-oncogene** are central to the development of **medullary thyroid carcinoma (MTC)**, especially in hereditary forms like **Multiple Endocrine Neoplasia type 2 (MEN 2)** [1], [2]. - Activating mutations in *RET* lead to constitutive activation of its tyrosine kinase domain, promoting uncontrolled cell growth and survival in **parafollicular C cells** [1], [3]. - Found in ~98% of hereditary MTC and ~40-50% of sporadic cases. *p53 (Incorrect)* - The **p53 tumor suppressor gene** is frequently mutated in a wide variety of human cancers, but it is not the primary driver in **medullary thyroid carcinoma**. - Its role is often seen in later-stage or more aggressive cancers, typically losing normal cell cycle control. *Her2/neu (Incorrect)* - The **HER2/neu (ERBB2) gene** encodes a receptor tyrosine kinase primarily associated with **breast cancer** and some **gastric cancers**, where its overexpression is a therapeutic target [1]. - Its overexpression is not a characteristic feature or driver mutation for **medullary thyroid carcinoma**. *Rb gene (Incorrect)* - The **retinoblastoma (Rb) gene** is a **tumor suppressor gene** crucial for regulating the cell cycle, and mutations are associated with retinoblastoma and other cancers like **osteosarcoma** and **small cell lung cancer**. - While it's a significant tumor suppressor, mutations in the *Rb gene* are not directly linked to the pathogenesis of **medullary thyroid carcinoma**. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Neoplasia, p. 292. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Endocrine System, pp. 1139-1140. [3] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Liver And Biliary System Disease, pp. 428-429.
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