Molecular Pathology Practice Questions

Q: What is the incidence of Down's syndrome directly proportional to?

Maternal age. The correct answer is **Maternal Age**. Down’s syndrome (Trisomy 21) is primarily caused by **meiotic non-disjunction**, where chromosomes fail to separate properly during oogenesis. As a woman ages, the primary oocytes (which have been arrested in Prophase I since birth) undergo "biological aging." This leads to a breakdown in the spindle apparatus and cohesive proteins, significantly increasing the risk of chromosomal errors. While the risk is approximately 1 in 1,500 at age 20, it rises sharply to 1 in 100 by age 40 and 1 in 25 by age 45. **Analysis of Incorrect Options:** * **Parity:** The number of previous pregnancies does not influence chromosomal non-disjunction; a first-time mother at age 40 has the same risk as a multiparous woman of the same age. * **Consanguinity:** This increases the risk of **autosomal recessive** disorders (e.g., Thalassemia, Wilson’s disease) by bringing together rare recessive alleles, but it does not cause numerical chromosomal aberrations like Trisomy 21. * **Mutations:** While Down’s syndrome is a genetic abnormality, it is typically a **cytogenetic error** (aneuploidy) rather than a point mutation or a specific gene defect. **High-Yield Clinical Pearls for NEET-PG:** * **Most common cause:** Meiotic non-disjunction (95% of cases), most often occurring during Maternal Meiosis I. * **Robertsonian Translocation:** Accounts for ~4% of cases; unlike non-disjunction, this type is **not** related to maternal age and carries a high recurrence risk if a parent is a carrier. * **Screening:** The "Quadruple Screen" (done at 15-20 weeks) typically shows **Low AFP, Low uE3, High hCG, and High Inhibin-A.** * **Ultrasound marker:** Increased Nuchal Translucency (NT) in the first trimester.

Q: A patient's karyotype shows the following. What is the expected clinical abnormality?

Gynecomastia with long thin limbs. ***Gynecomastia with long thin limbs*** - The karyotype **47,XXY** (Klinefelter syndrome) causes **hypogonadism** leading to decreased testosterone and relative estrogen excess, resulting in **gynecomastia**. - Patients typically present with **tall stature**, **long limbs**, and **eunuchoid body habitus** due to delayed epiphyseal closure from testosterone deficiency. *Short stature with polydactyly* - **Polydactyly** is associated with conditions like **Patau syndrome (trisomy 13)** or **Ellis-van Creveld syndrome**, not Klinefelter syndrome. - Klinefelter syndrome typically causes **tall stature**, not short stature, due to prolonged growth before epiphyseal fusion. *Webbed neck with widely spaced nipples* - These features are characteristic of **Turner syndrome (45,X)**, which affects females and causes **short stature** and **ovarian dysgenesis**. - Klinefelter syndrome affects **males** and does not involve **pterygium colli** (webbed neck) or chest wall abnormalities. *Rocker bottom feet* - This feature is classically associated with **Edwards syndrome (trisomy 18)** and involves a **convex plantar surface**. - Klinefelter syndrome does not typically cause **skeletal foot deformities** but rather affects **sexual development** and **body proportions**.

Q: All of the following are true about tumors associated with BRCA-1 except:

Hormone receptor positive. **Explanation:** The correct answer is **A (Hormone receptor positive)** because BRCA-1 associated breast cancers are characteristically **Triple Negative** (ER negative, PR negative, and HER2/neu negative). **1. Why Option A is the correct answer (The Exception):** BRCA-1 mutations are associated with a specific molecular phenotype known as "Basal-like" carcinoma. Unlike sporadic breast cancers or BRCA-2 mutations, BRCA-1 tumors typically lack estrogen and progesterone receptors. Therefore, they do not respond to hormonal therapies like Tamoxifen or Aromatase inhibitors. **2. Analysis of Incorrect Options:** * **B. Poorly differentiated:** BRCA-1 tumors are histologically aggressive. they are typically high-grade (Grade 3), show a high mitotic index, and often exhibit pushing margins and lymphocytic infiltration. * **C. Chromosome 17:** The BRCA-1 gene is located on the long arm of **Chromosome 17 (17q21)**. (Note: BRCA-2 is on Chromosome 13q12). * **D. Early age onset:** Hereditary breast cancers present significantly earlier than sporadic cases, often in the 30s or 40s. **Clinical Pearls for NEET-PG:** * **BRCA-1 vs. BRCA-2:** BRCA-1 has a higher risk of **Ovarian cancer** (up to 40%) compared to BRCA-2 (up to 20%). BRCA-2 is more strongly associated with **Male breast cancer** and is typically **ER/PR positive**. * **Prophylaxis:** Bilateral Salpingo-oophorectomy (BSO) reduces the risk of ovarian cancer by 80-90% and also significantly reduces breast cancer risk if performed pre-menopausally. * **Associated Tumors:** BRCA-1 is also linked to prostate and colon cancers, while BRCA-2 is linked to pancreatic, prostate, and gallbladder cancers.

Q: What is the rapid method for chromosome identification in intersex conditions?

FISH. **Explanation:** The identification of chromosomal sex is a critical step in the management of intersex conditions (Disorders of Sex Development). **Why FISH is the correct answer:** **Fluorescence In Situ Hybridization (FISH)** is the preferred rapid method because it uses fluorescently labeled DNA probes that bind to specific sequences on the X and Y chromosomes. It can be performed on **interphase nuclei** (non-dividing cells), meaning it does not require a time-consuming cell culture. Results are typically available within **24–48 hours**, making it ideal for urgent gender assignment or clinical decision-making in neonates [1]. [1] **Why the other options are incorrect:** * **Karyotyping:** While it is the "Gold Standard" for definitive diagnosis, it requires cells to be in metaphase [2]. This necessitates a cell culture that takes **7–14 days**, making it too slow for immediate rapid identification. * **PCR (Polymerase Chain Reaction):** Though very fast and sensitive for detecting specific genes (like the *SRY* gene), it does not provide a comprehensive view of chromosome morphology or mosaicism as effectively as FISH in a clinical setting for intersex. * **SSCP (Single Strand Conformation Polymorphism):** This is a technique used to detect small mutations or polymorphisms in DNA sequences, not for identifying whole chromosomes or numerical abnormalities. **High-Yield Clinical Pearls for NEET-PG:** * **Barr Body:** A condensed, inactive X chromosome found in females. The number of Barr bodies = (Total X chromosomes - 1). * **SRY Gene:** Located on the short arm of the Y chromosome (Yp11.3); its presence determines male sexual differentiation. * **Gold Standard for Aneuploidy:** Karyotyping remains the definitive test for Turner (45,XO) and Klinefelter (47,XXY) syndromes, though FISH is the fastest initial screen [1].

Question 1

Which of the following types of karyotyping is performed under light microscopy?

Accepted Answer

G banding

Answer

R banding

Answer

Q banding

Answer

C banding

Question 2

Which of the following is NOT a chromosomal breakage syndrome?

Accepted Answer

Duchenne muscular dystrophy

Answer

Fragile X syndrome

Answer

Bloom syndrome

Answer

Ataxia telangiectasia

Question 3

Which test is used to differentiate between the chromosomal patterns of a normal cell and a cancer cell?

Accepted Answer

Comparative genomic hybridization

Answer

Fluorescence in situ hybridization (FISH)

Answer

Polymerase chain reaction (PCR)

Answer

Karyotyping

Question 4

What is the incidence of Down's syndrome directly proportional to?

Accepted Answer

Maternal age

Answer

Parity

Answer

Consanguinity

Answer

Mutations

Question 5

A patient's karyotype shows the following. What is the expected clinical abnormality?

Accepted Answer

Gynecomastia with long thin limbs

Answer

Short stature with polydactyly

Answer

Webbed neck with widely spaced nipples

Answer

Rocker bottom feet

Question 6

What is the total number of chromosomes typically found in an individual with Turner syndrome?

Accepted Answer

45

Answer

47

Answer

46

Answer

42

Question 7

All of the following are true about tumors associated with BRCA-1 except:

Accepted Answer

Hormone receptor positive

Answer

Poorly differentiated

Answer

Chromosome 17

Answer

Early age onset

Question 8

Xeroderma pigmentosum is characterized by

Accepted Answer

Inability to repair sunlight induced damage to DNA

Answer

Autosomal dominant inheritance

Answer

Irregular accumulation of melanin in the basal cell layer

Answer

Acanthosis of epithelium with elongation of rete ridges

Question 9

What is the rapid method for chromosome identification in intersex conditions?

Accepted Answer

FISH

Answer

PCR

Answer

SSCP

Answer

Karyotyping

Question 10

What is true about Klinefelter syndrome?

Accepted Answer

XXY

Answer

XO

Answer

Testes are absent

Answer

Female hypogonadism

Molecular Pathology — MCQs

Molecular Pathology — MCQs

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