Molecular Pathology Practice Questions

Q: Division of a chromosome perpendicular to its normal axis of division leads to which of the following?

Isochromosome. ### Explanation **Correct Option: B. Isochromosome** An **isochromosome** is a structural chromosomal abnormality formed when a chromosome divides **transversely (perpendicular)** to its longitudinal axis rather than the normal longitudinal (vertical) division. [1] * **Mechanism:** Instead of separating into two identical sister chromatids, the centromere splits horizontally. This results in one chromosome consisting of two short arms (p) and another consisting of two long arms (q). [1] * **Consequence:** The resulting cell has a loss of one arm's genetic material and a duplication of the other. The most common clinical example is **i(12p)** in germ cell tumors and **i(Xq)**, which is seen in approximately 15% of cases of **Turner Syndrome** (45,X/46,X,i(Xq)). [1] **Analysis of Incorrect Options:** * **A. Ring chromosome:** Formed when a chromosome sustains breaks at both ends (telomeres), followed by the fusion of the damaged "sticky" ends. This results in a circular structure and loss of distal genetic material. * **C & D. Acrocentric and Subtelocentric chromosomes:** These terms describe the **normal morphology** of chromosomes based on centromere position. * *Acrocentric:* Centromere is very near one end (e.g., chromosomes 13, 14, 15, 21, 22). * *Subtelocentric:* Centromere is located between the midpoint and the tip. These are not results of abnormal division. **High-Yield Clinical Pearls for NEET-PG:** * **Turner Syndrome:** The most common structural abnormality is the isochromosome of the long arm of X [i(Xq)]. [1] * **Robertsonian Translocation:** Occurs only in **acrocentric** chromosomes; it involves the fusion of two long arms and the loss of two short arms. * **Philadelphia Chromosome:** A reciprocal translocation t(9;22) seen in CML. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Genetic Disorders, pp. 169-170.

Q: Which syndrome is characterized by the occurrence of both colorectal and endometrial cancers?

Lynch syndrome. **Explanation:** **Lynch Syndrome (Hereditary Non-Polyposis Colorectal Cancer - HNPCC)** is the correct answer. It is an autosomal dominant condition caused by germline mutations in **DNA Mismatch Repair (MMR) genes** (MLH1, MSH2, MSH6, and PMS2), leading to microsatellite instability. While it carries the highest risk for colorectal cancer (CRC), the most common extra-colonic manifestation is **Endometrial Cancer**. In fact, for female patients with Lynch syndrome, the risk of endometrial cancer often equals or exceeds the risk of CRC. **Analysis of Incorrect Options:** * **Cowden Syndrome:** Part of the PTEN hamartoma tumor syndrome. It is characterized by multiple hamartomas, macrocephaly, and a high risk of **Breast, Thyroid (follicular), and Endometrial cancers**, but it is not primarily defined by the CRC-Endometrial duo. * **Turcot’s Syndrome:** A variant of polyposis syndromes (FAP or Lynch) characterized by the association of **Colorectal tumors and Central Nervous System (CNS) tumors** (Medulloblastoma in FAP; Glioblastoma in Lynch). * **Juvenile Polyposis Syndrome (JPS):** Characterized by multiple hamartomatous polyps in the GI tract. While it increases the risk of GI cancers, it is not typically associated with endometrial malignancy. **High-Yield Clinical Pearls for NEET-PG:** * **Amsterdam II Criteria (3-2-1 rule):** 3 relatives with Lynch-associated cancer, 2 successive generations, 1 diagnosed before age 50. * **Lynch-associated cancers:** Colorectal (right-sided predominance), Endometrial, Ovarian, Gastric, and Small Bowel. * **Screening:** For Lynch syndrome, colonoscopy is recommended every 1–2 years starting at age 20–25. Prophylactic hysterectomy and bilateral salpingo-oophorectomy (BSO) are often considered after childbearing is complete.

Q: What is the diagnosis suggested by the following karyotype?

Cri du chat syndrome. ***Cri du chat syndrome*** - The karyotype showing **deletion of the short arm of chromosome 5 (del 5p)** is diagnostic of Cri du chat syndrome. - Clinical features include **characteristic cat-like cry** in infants, **microcephaly**, **intellectual disability**, and **distinctive facial features**. *Down's syndrome* - Characterized by **trisomy 21** karyotype (47,XY,+21 or 47,XX,+21), not a deletion on chromosome 5. - Clinical features include **epicanthal folds**, **simian crease**, and **intellectual disability** with cardiac defects. *Turner's syndrome* - Shows **monosomy X** karyotype (45,X) or mosaic patterns, involving sex chromosomes not chromosome 5. - Clinical features include **short stature**, **webbed neck**, **shield chest**, and **ovarian dysgenesis**. *Patau Syndrome* - Demonstrates **trisomy 13** karyotype (47,XY,+13 or 47,XX,+13), not involving chromosome 5 deletion. - Clinical features include **holoprosencephaly**, **cleft lip/palate**, **polydactyly**, and severe **intellectual disability**.

Question 1

Division of a chromosome perpendicular to its normal axis of division leads to which of the following?

Accepted Answer

Isochromosome

Answer

Ring chromosome

Answer

Acrocentric chromosome

Answer

Subtelocentric chromosome

Question 2

Which of the following procedures is routinely used for karyotyping using light microscopy?

Accepted Answer

G-banding

Answer

C-banding

Answer

Q-banding

Answer

BrdU-staining

Question 3

Which one of the following is NOT a characteristic feature of an autosomal recessive disorder?

Accepted Answer

Wide variation in phenotype within a family

Answer

Males and females are equally affected

Answer

Parents of an affected child are usually heterozygous carriers

Answer

Display a horizontal pattern in pedigrees

Question 4

Multifactorial inheritance is most likely to play a role in which of the following conditions?

Accepted Answer

Cleft lip

Answer

Marfan's syndrome

Answer

Down's syndrome

Answer

Erythroblastosis fetalis

Question 5

Von Hippel-Lindau disease is associated with all the following except?

Accepted Answer

Hemangioblastomas

Answer

Endolymphatic sac tumors

Answer

Pheochromocytoma

Answer

Islet cell tumors

Question 6

Klinefelter syndrome is associated with all, except:

Accepted Answer

Barr body absent

Answer

Delayed puberty

Answer

Male phenotype

Answer

Azoospermia

Question 7

Which of the following is false regarding Noonan syndrome?

Accepted Answer

It is autosomal recessive.

Answer

It involves mutations in chromosome 12.

Answer

Both males and females are affected.

Answer

Low levels of clotting factors XI and XII are present.

Question 8

Which syndrome is characterized by the occurrence of both colorectal and endometrial cancers?

Accepted Answer

Lynch syndrome

Answer

Cowden syndrome

Answer

Turcot's syndrome

Answer

Juvenile polyposis syndrome

Question 9

What is the diagnosis suggested by the following karyotype?

Accepted Answer

Cri du chat syndrome

Answer

Down's syndrome

Answer

Turner's syndrome

Answer

Patau Syndrome

Question 10

Down's syndrome is associated with mental retardation. Which of the following chromosomal abnormalities are not typically found in Down's syndrome?

Accepted Answer

Deletion of chromosome 21

Answer

Trisomy 21

Answer

Translocation involving chromosome 21 (e.g., t(13,21), t(21,21))

Answer

Mosaicism with trisomy 21

Molecular Pathology — MCQs

Molecular Pathology — MCQs

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