Molecular Pathology Practice Questions

Q: Mutation in Marfan's syndrome is in which gene?

Fibrillin I. **Explanation:** **Marfan Syndrome** is an autosomal dominant connective tissue disorder caused by a mutation in the **FBN1 gene** located on **chromosome 15q21**. This gene encodes **Fibrillin-1**, a large glycoprotein that serves as a structural component of calcium-binding microfibrils. These microfibrils form a scaffold for elastin deposition and regulate **TGF-β (Transforming Growth Factor beta)** signaling. A deficiency in Fibrillin-1 leads to weakened connective tissue and excessive TGF-β activation, resulting in the classic skeletal, ocular, and cardiovascular manifestations [1]. **Analysis of Incorrect Options:** * **Fibrillin II (Option B):** Mutations in the *FBN2* gene (chromosome 5) cause **Congenital Contractural Arachnodactyly (Beals Syndrome)**. While it shares skeletal features with Marfan syndrome (like long limbs), it is characterized by "crumpled" ears and joint contractures rather than aortic involvement. * **Collagen I (Option C):** Mutations here are associated with **Osteogenesis Imperfecta** (brittle bone disease) and certain types of Ehlers-Danlos Syndrome (EDS). * **Collagen IV (Option D):** This is a major component of the basement membrane. Mutations lead to **Alport Syndrome** (hereditary nephritis and sensorineural deafness). **High-Yield Clinical Pearls for NEET-PG:** * **Cardiovascular:** Aortic root dilation and **dissection** (most common cause of death) and Mitral Valve Prolapse (MVP). * **Ocular:** **Ectopia lentis** (dislocation of the lens), typically **upward and outward** (superior-temporal) [1]. * **Skeletal:** Arachnodactyly (positive Wrist and Thumb signs), Pectus excavatum/carinatum, and increased arm span to height ratio (>1.05). * **Differentiating Factor:** Unlike Homocystinuria (which also has Marfanoid habitus), Marfan syndrome patients have **normal intellect** and an upward lens dislocation (Homocystinuria is downward).

Q: The following karyotype is suggestive of which disorder?

Patau syndrome. ***Patau syndrome*** - Characterized by **Trisomy 13** (47,+13 karyotype), which involves an extra chromosome in **group D chromosomes**. - Clinical features include severe **intellectual disability**, **cleft lip/palate**, **polydactyly**, and **holoprosencephaly**. *Edward's syndrome* - Caused by **Trisomy 18** (47,+18 karyotype), involving an extra chromosome in **group E chromosomes**. - Presents with **clenched fists**, **rocker-bottom feet**, and severe **growth retardation**. *Alagille syndrome* - Results from **JAG1 gene deletion/mutation** at chromosome **20p12**, not a trisomy condition. - Characterized by **bile duct paucity**, **butterfly vertebrae**, and **triangular facies**. *Williams syndrome* - Caused by **microdeletion at 7q11.23** involving **ELASTIN gene**, not chromosomal aneuploidy. - Features include **supravalvular aortic stenosis**, **stellate iris pattern**, and **cocktail party personality**.

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.

Question 1

Mutation in Marfan's syndrome is in which gene?

Accepted Answer

Fibrillin I

Answer

Fibrillin II

Answer

Collagen I

Answer

Collagen IV

Question 2

The following karyotype is suggestive of which disorder?

Accepted Answer

Patau syndrome

Answer

Edward's syndrome

Answer

Alagille syndrome

Answer

Williams syndrome

Question 3

What is the approximate resolution of visualizing chromosomes through a light microscope?

Accepted Answer

5 megabases (mb)

Answer

5 kilobases (Kb)

Answer

50 megabases (mb)

Answer

500 kilobases (Kb)

Question 4

Which of the following is a clinical feature of 22q11 deletion syndrome?

Accepted Answer

Conotruncal abnormalities

Answer

Hypercalcemia

Answer

Thymic hyperplasia

Answer

Dysmorphogenesis of the 1st and 2nd pharyngeal pouches

Question 5

What is the most common trisomy among the following?

Accepted Answer

Trisomy 21

Answer

Trisomy 18

Answer

Trisomy 13

Answer

Trisomy 5

Question 6

Which one of the following statements is FALSE regarding autosomal dominant disorders?

Accepted Answer

The recurrence risk is 25% for parents with a previously affected child.

Answer

Mutated genes can express themselves in the heterozygous state.

Answer

Males and females are equally affected.

Answer

These disorders typically involve defects of structural proteins or receptors.

Question 7

Premutation is seen in which of the following conditions?

Accepted Answer

Trinucleotide repeat mutation

Answer

Genomic imprinting

Answer

Mitochondrial mutation

Answer

Gonadal mosaicism

Question 8

Karyotyping is done with all, except:

Accepted Answer

Blood monocyte

Answer

Blood lymphocyte

Answer

Amnion

Answer

Fibroblast

Question 9

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 10

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

Molecular Pathology — MCQs

Molecular Pathology — MCQs

On this page

Practice by Chapter

Want unlimited practice?