Molecular Pathology — MCQs

Q: Which of the following is not a chromosome breakage disorder?

Duchenne muscular dystrophy. ***Duchenne muscular dystrophy*** - Duchenne muscular dystrophy is primarily a **muscle degeneration disorder** caused by mutations in the **dystrophin gene**, not a chromosome breakage disorder. - It does not involve issues with **chromosomal stability** or breakage, unlike the others listed. *Ataxia telangiectasia* - Ataxia telangiectasia is associated with defects in **DNA repair mechanisms**, leading to **chromosome breakage** and instability [1]. - Patients exhibit progressive **ataxia**, **telangiectasia**, and increased sensitivity to radiation. *Fanconi anemia* - Fanconi anemia is characterized by a defect in the **DNA repair pathway**, resulting in increased **chromosome breakage** [1]. - It is associated with **bone marrow failure** and development of various malignancies. *Bloom syndrome* - Bloom syndrome results from defects in the **BLM gene**, leading to **genomic instability** and an increased rate of chromosome breakage [1]. - This condition causes symptoms like **short stature**, **facial lesions**, and a predisposition to cancer. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Neoplasia, pp. 322-323.

Q: Which of the following is a channelopathy?

Anderson Tawil Syndrome. ***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.

Q: Which banding technique is most commonly used for karyotyping?

G banding. ***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.

Q: What is the genotype of Klinefelter syndrome?

47,XXY. ***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.

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Principles of Molecular Pathology

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