Molecular Pathology Practice Questions

Q: Li-Fraumeni syndrome occurs due to mutation in which gene?

TP53. ***Correct Answer: TP53*** - Li-Fraumeni syndrome is an autosomal dominant hereditary cancer syndrome linked to germline mutations in the **TP53 tumor suppressor gene**. - The TP53 gene encodes the **p53 protein**, a critical regulator of the cell cycle and apoptosis, often called the "guardian of the genome." *Incorrect: CDKN2A* - Mutations in the **CDKN2A gene** are primarily associated with familial melanoma and pancreatic cancer. - This gene encodes two tumor suppressor proteins, **p16INK4a** and **p14ARF**, which regulate the cell cycle. *Incorrect: PTEN* - The **PTEN gene** is associated with Cowden syndrome, which increases the risk of benign and malignant tumors in various tissues, including breast, thyroid, and endometrium. - PTEN is a tumor suppressor gene involved in cell growth, proliferation, and apoptosis. *Incorrect: MDM2* - The **MDM2 gene** is an oncogene that inactivates the p53 tumor suppressor protein. - While it interacts with p53, MDM2 mutations or overexpression are not the primary cause of Li-Fraumeni syndrome; rather, they contribute to cancer development by inhibiting p53 function.

Q: What is the chromosomal defect associated with Prader-Willi syndrome?

Chromosome 15. ***Chromosome 15*** - **Prader-Willi syndrome** is characterized by a deletion or other abnormality on the **paternal copy** of **chromosome 15q11-q13** [1]. - This specific region contains genes critical for normal development and function, whose altered expression due to the paternal origin causes the syndrome [1]. *Chromosome 5* - Abnormalities of chromosome 5 are associated with conditions like **Cri-du-chat syndrome**, which involves a deletion on the short arm (5p). - This is not linked to the characteristic symptoms of Prader-Willi syndrome. *Chromosome 10* - Defects on chromosome 10 are associated with various other genetic disorders, such as **multiple endocrine neoplasia type 2 (MEN 2)** or **Cowden syndrome**. - There is no established direct link between chromosome 10 abnormalities and Prader-Willi syndrome. *Chromosome 21* - **Trisomy 21** is the genetic defect responsible for **Down syndrome** (presence of an extra copy of chromosome 21) [2]. - While a common chromosomal abnormality, it presents with a distinct set of clinical features different from Prader-Willi syndrome [2]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Genetic Disorders, pp. 182-183. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Genetic Disorders, pp. 171-172.

Q: Which of the following conditions is characterized by the absence of Barr bodies?

Turner syndrome. ***Turner syndrome*** - Females with **Turner syndrome** have a 45,XO karyotype, meaning they have only one X chromosome. - Since a **Barr body** is formed from the inactivation of one X chromosome in normal females (46,XX), individuals with Turner syndrome have **no Barr bodies** due to the absence of a second X chromosome. *Klinefelter syndrome* - Individuals with **Klinefelter syndrome** typically have a 47,XXY karyotype, meaning they have two X chromosomes. - The presence of two X chromosomes leads to the formation of **one Barr body** (from inactivation of one of the two X chromosomes), making this option incorrect. *Down's syndrome* - **Down's syndrome** is caused by trisomy 21 (extra copy of chromosome 21), which is an autosomal abnormality. - The number of Barr bodies in individuals with Down's syndrome depends on their sex chromosome complement (normal pattern: 46,XX females have one Barr body, 46,XY males have none). *Marfan's syndrome* - **Marfan's syndrome** is an autosomal dominant disorder affecting connective tissue, caused by a mutation in the **FBN1 gene**. - This condition does not involve abnormalities in sex chromosomes, so the number of Barr bodies follows the normal pattern (one in 46,XX females, none in 46,XY males).

Q: Which gene is primarily associated with Cowden syndrome?

PTEN. ***PTEN*** - Cowden syndrome is an **autosomal dominant** inherited disorder caused by germline mutations in the **PTEN (phosphatase and tensin homolog) tumor suppressor gene**. - The PTEN gene plays a crucial role in cell growth, proliferation, and apoptosis, and its dysfunction leads to uncontrolled cell growth and the development of multiple **hamartomas** and increased cancer risk. *TP53* - Mutations in the **TP53 gene** are primarily associated with Li-Fraumeni syndrome, a different inherited cancer predisposition syndrome characterized by a high risk of various cancers including sarcomas, breast cancer, and adrenocortical carcinoma. - While both inherited cancer syndromes involve tumor suppressor gene mutations, the specific gene affected and the clinical presentation differ significantly. *RB1* - The **RB1 gene** is a tumor suppressor gene primarily associated with **retinoblastoma**, a rare childhood eye cancer, and an increased risk of other cancers like osteosarcoma. - It plays a critical role in cell cycle regulation, and its mutation leads to uncontrolled cell division in the retina and other tissues. *KRAS* - The **KRAS gene** is an oncogene, not a tumor suppressor gene, and its mutations are frequently found in various sporadic cancers, particularly **colorectal cancer**, pancreatic cancer, and lung cancer. - KRAS mutations lead to constitutive activation of signaling pathways that promote cell growth and survival, but they are not the primary genetic cause of inherited Cowden syndrome.

Q: Structure of chromosomes is studied by?

G-banding. ***G-banding*** - G-banding is the most commonly used method for the **detailed examination of chromosomes**, allowing visualization of banding patterns [1][2]. - It facilitates the identification of **chromosomal abnormalities** and is essential in **cytogenetic studies** [1][2]. *Q-banding* - Q-banding reveals a different pattern that is primarily used for **detection of specific chromosome markers** but is less common than G-banding. - It is more useful for cases requiring **fluorescent bright bands** but not for overall structural analysis. *C-banding* - C-banding specifically highlights the **centromeric regions** of chromosomes, not the overall structure. - It is limited in scope compared to G-banding since it doesn't provide a complete picture of chromosome morphology. *Brd V-staining* - Brd V-staining focuses on specific **DNA regions** and is related to the **visualization of viral DNA** in infected cells rather than chromosome structure. - It does not offer insights into the **general structural characteristics** of chromosomes like G-banding does. **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: Which genetic condition is considered the most lethal due to monosomy?

Autosomal monosomy. ***Autosomal monosomy*** - **Autosomal monosomy** is the most lethal form of monosomy because it involves the loss of an entire autosome, leading to a severe imbalance in gene dosage. [1] - The human body cannot typically survive with the loss of a whole autosome, resulting in early embryonic or fetal demise. [1] *Chromosomal monosomy* - This is a broader term that includes both **autosomal monosomy** and **sex chromosome monosomy**. - While many forms of chromosomal monosomy are lethal, **sex chromosome monosomy (e.g., Turner syndrome)** is survivable, making the general term "chromosomal monosomy" less specific for the *most lethal* condition. [1] *Autosomal trisomy* - **Autosomal trisomy** involves an extra copy of an autosome (e.g., Trisomy 21 for Down syndrome), which, while causing significant health issues, is generally less lethal than the complete loss of an autosome. [1] - Many individuals with autosomal trisomies can survive to birth and beyond, unlike most cases of autosomal monosomy. [1] *Chromosomal trisomy* - This refers to having an extra copy of any chromosome, including **autosomes** and **sex chromosomes**. - While conditions like **Trisomy 13 (Patau syndrome)** and **Trisomy 18 (Edwards syndrome)** are highly lethal, the presence of *extra* genetic material is typically less universally lethal than the *absence* of an entire autosome. [1] **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Genetic Disorders, pp. 168-169.

Question 1

Which of the following statements about Von Hippel-Lindau (VHL) syndrome is true?

Accepted Answer

Regular screening for clear cell carcinoma of the kidneys is essential.

Answer

It is an autosomal recessive condition.

Answer

Central nervous system involvement is rare.

Answer

The VHL gene acts as a growth promoter.

Question 2

Li-Fraumeni syndrome occurs due to mutation in which gene?

Accepted Answer

TP53

Answer

CDKN2A

Answer

PTEN

Answer

MDM2

Question 3

Which of the following statements about FISH (Fluorescence In Situ Hybridization) is false?

Accepted Answer

Requires DNA polymerase

Answer

Used to detect copy number variations

Answer

Used to detect balanced translocations

Answer

Requires fluorescent probes

Question 4

What is the chromosomal defect associated with Prader-Willi syndrome?

Accepted Answer

Chromosome 15

Answer

Chromosome 5

Answer

Chromosome 10

Answer

Chromosome 21

Question 5

Diagnose the disorder by looking at the karyotype.

Accepted Answer

Down syndrome.

Answer

Patau syndrome.

Answer

Turner syndrome.

Answer

Klinefelter syndrome.

Question 6

Which of the following conditions is characterized by the absence of Barr bodies?

Accepted Answer

Turner syndrome

Answer

Klinefelter syndrome

Answer

Down's syndrome

Answer

Marfan's syndrome

Question 7

Which gene is primarily associated with Cowden syndrome?

Accepted Answer

PTEN

Answer

RB1

Answer

KRAS

Answer

TP53

Question 8

Structure of chromosomes is studied by?

Accepted Answer

G-banding

Answer

C-banding

Answer

Q-banding

Answer

BrdU staining

Question 9

Which genetic condition is considered the most lethal due to monosomy?

Accepted Answer

Autosomal monosomy

Answer

Chromosomal monosomy

Answer

Autosomal trisomy

Answer

Chromosomal trisomy

Question 10

Which of the following is a chromosomal instability syndrome?

Accepted Answer

Bloom syndrome

Answer

Fanconi anemia

Answer

Ataxia-telangiectasia

Answer

None of the options

Molecular Pathology — MCQs

Molecular Pathology — MCQs

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