Chromosomal Disorders — MCQs
All the following are characteristic features of Turner syndrome except:
All of the following are true about Down syndrome except for one.
What is the name of the syndrome associated with the deletion of chromosome 22?
Select the FALSE combination of chromosomal pattern and the syndrome:
In which condition is the presence of an extra pair of ribs sometimes observed?
A child presents with a webbed neck, short stature, and a low posterior hairline. What is the most likely diagnosis?
Which investigation is the gold standard for diagnosing Edwards syndrome?
What term describes a chromosomal number that is an exact multiple of 23?
Number of chromosomes in Klinefelter syndrome:
Which of the following conditions is characterized by the presence of telangiectasia?
Chromosomal Disorders Indian Medical PG Practice Questions and MCQs
Question 1: All the following are characteristic features of Turner syndrome except:
- A. Cubitus valgus
- B. Webbing of Neck
- C. Umbilical Hernia (Correct Answer)
- D. Coarctation of Aorta
- E. Short stature
Explanation: ***Umbilical Hernia*** - While various **congenital anomalies** can occur in individuals with Turner syndrome, an **umbilical hernia** is not considered a characteristic or commonly associated feature. - The other options represent classic physical findings frequently observed in Turner syndrome. *Cubitus valgus* - This is a common orthopedic finding in Turner syndrome, characterized by an **increased carrying angle** at the elbow. - It results from the skeletal dysplasias associated with the **45,X karyotype**. *Webbing of Neck* - **Pterygium colli**, or webbing of the neck, is a classic and highly recognizable feature of Turner syndrome. - It is caused by **lymphatic abnormalities** during fetal development. *Coarctation of Aorta* - **Cardiovascular malformations**, particularly **coarctation of the aorta** and **bicuspid aortic valve**, are common and serious complications of Turner syndrome. - These conditions require careful monitoring and intervention due to their potential impact on health. *Short stature* - **Short stature** is one of the most universal features of Turner syndrome, present in over **95% of cases**. - Average adult height without growth hormone treatment is approximately **143-145 cm (4'8"-4'9")**. - Results from haploinsufficiency of the **SHOX gene** on the X chromosome.
Question 2: All of the following are true about Down syndrome except for one.
- A. Incidence of Robertsonian translocation is 1:1000 (Correct Answer)
- B. Most common cause is trisomy 21
- C. Mosaicism 21 has no association with maternal age
- D. Extra chromosome is of maternal origin
- E. Incidence increases with advanced maternal age
Explanation: **Incidence of Robertsonian translocation is 1:1000** - This statement is **not accurate** for Down syndrome. Robertsonian translocation accounts for only about **3-4% of Down syndrome cases**, not a general population incidence of 1:1000. - The vast majority of Down syndrome cases (~95%) are due to trisomy 21 from nondisjunction, not translocation. - This is the **correct answer** as it is the FALSE statement. *Extra chromosome is of maternal origin* - In approximately **90-95% of Down syndrome cases**, the extra copy of chromosome 21 originates from the mother due to **nondisjunction** during meiosis. - This maternal origin is strongly correlated with **advanced maternal age**. *Most common cause is trisomy 21* - **Trisomy 21** (due to meiotic nondisjunction) accounts for about **95% of all Down syndrome cases**, making it the most common genetic mechanism. - This results in three separate copies of chromosome 21 in all body cells. *Mosaicism 21 has no association with maternal age* - **Mosaic Down syndrome** occurs when nondisjunction happens *after fertilization* in early embryonic development, leading to a mixture of cells with normal and trisomic cells. - Because it is a **post-zygotic event**, its incidence is independent of **maternal age**, unlike full trisomy 21. *Incidence increases with advanced maternal age* - **TRUE statement** - The risk of Down syndrome (particularly trisomy 21) increases significantly with **maternal age**. - Risk is approximately 1:1500 at age 20, 1:1000 at age 30, 1:400 at age 35, and 1:100 at age 40. - This is due to increased risk of meiotic nondisjunction in older oocytes.
Question 3: What is the name of the syndrome associated with the deletion of chromosome 22?
- A. Down syndrome
- B. Di George syndrome (Correct Answer)
- C. Turner syndrome
- D. Klinefelter syndrome
- E. Prader-Willi syndrome
Explanation: ***Di George syndrome*** - Di George syndrome, also known as **22q11.2 deletion syndrome**, is caused by a deletion on the long arm of chromosome 22. - This syndrome is associated with varied clinical features, including **congenital heart defects**, **thymic hypoplasia** (leading to immune deficiencies), **hypocalcemia** due to parathyroid hypoplasia, and characteristic facial features. *Down syndrome* - Down syndrome is caused by a **trisomy of chromosome 21**, meaning there's an extra copy of chromosome 21. - It is characterized by intellectual disability, distinctive facial features, and developmental delays, and is not associated with chromosome 22 deletion. *Turner syndrome* - Turner syndrome is a chromosomal condition affecting females, characterized by the partial or complete absence of one of the **X chromosomes (45, X0)**. - It leads to short stature, ovarian dysfunction, and characteristic physical features, unrelated to chromosome 22. *Klinefelter syndrome* - Klinefelter syndrome is a chromosomal disorder in males resulting from an extra **X chromosome (47, XXY)**. - Individuals often experience hypogonadism, reduced fertility, and abnormal body proportions, which is distinct from a deletion on chromosome 22. *Prader-Willi syndrome* - Prader-Willi syndrome is caused by a **deletion of paternal chromosome 15q11-q13** or maternal uniparental disomy. - It presents with hypotonia, hyperphagia, obesity, intellectual disability, and hypogonadism, unrelated to chromosome 22 deletion.
Question 4: Select the FALSE combination of chromosomal pattern and the syndrome:
- A. Swyer's syndrome-46XY
- B. Klinefelter's syndrome-47XXY
- C. Turner's syndrome-45XO
- D. Mayer Rokitansky-46XY (Correct Answer)
Explanation: ***Mayer Rokitansky-46XY*** - Mayer-Rokitansky-Küster-Hauser (MRKH) syndrome is characterized by **vaginal agenesis** and **uterine anomalies** in individuals with a normal **46,XX** **karyotype**, making 46,XY an incorrect chromosomal pattern for this syndrome. - Individuals with MRKH have female external genitalia and normal ovarian function, differentiating it from disorders of sexual development involving sex chromosome abnormalities. *Swyer's syndrome-46XY* - This is a **correct** combination; Swyer's syndrome is a form of **XY gonadal dysgenesis** where individuals have a **46,XY karyotype** but develop female external genitalia due a non-functional SRY gene [2]. - These individuals typically present with **primary amenorrhea** and **streak gonads**, requiring hormone replacement therapy and gonadectomy to prevent gonadoblastoma. *Klinefelter's syndrome-47XXY* - This is a **correct** combination; Klinefelter's syndrome is characterized by the presence of an **extra X chromosome** in biological males, resulting in a **47,XXY karyotype** [2]. - Affected individuals typically exhibit **hypogonadism**, **infertility**, **gynecomastia**, and often have a taller stature [3]. *Turner's syndrome-45XO* - This is a **correct** combination; Turner's syndrome is characterized by the **absence or partial absence of one X chromosome** in females, resulting in a **45,XO karyotype** [1]. - Clinical features include **short stature**, **ovarian dysgenesis** (streak gonads), **primary amenorrhea**, and distinctive physical features such as a **webbed neck** and **broad chest** [1].
Question 5: In which condition is the presence of an extra pair of ribs sometimes observed?
- A. Down syndrome
- B. Turner syndrome (Correct Answer)
- C. Holt-Oram syndrome
- D. Fibrous dysplasia
- E. Klinefelter syndrome
Explanation: ***Turner syndrome*** - **Turner syndrome** (45,X) is often associated with skeletal abnormalities, including an extra pair of ribs (cervical ribs) in some cases. - Other common skeletal features include **short stature**, a **shield chest**, and **cubitus valgus**. *Down syndrome* - **Down syndrome** (trisomy 21) is characterized by specific facial features, intellectual disability, and congenital heart defects. - While it can manifest with various skeletal anomalies, an extra pair of ribs is not a characteristic feature. *Klinefelter syndrome* - **Klinefelter syndrome** (47,XXY) is characterized by hypogonadism, tall stature, gynecomastia, and learning difficulties. - Skeletal features may include long limbs and decreased bone density, but cervical ribs are not typically associated with this condition. *Holt-Oram syndrome* - **Holt-Oram syndrome** is a genetic disorder affecting heart and limb development, specifically the upper limbs (thumb abnormalities, phocomelia). - It does not typically involve the presence of an extra pair of ribs. *Fibrous dysplasia* - **Fibrous dysplasia** is a bone disorder where normal bone is replaced by fibrous tissue, leading to weakened bone and fractures. - It is a localized bone condition and does not involve the presence of supernumerary ribs.
Question 6: A child presents with a webbed neck, short stature, and a low posterior hairline. What is the most likely diagnosis?
- A. Edwards syndrome
- B. Turner syndrome (Correct Answer)
- C. Patau syndrome
- D. Down syndrome
- E. Noonan syndrome
Explanation: ***Turner syndrome*** - **Turner syndrome** is characterized by the presence of a **single X chromosome (45,XO)** and is associated with a **webbed neck**, **short stature**, and a **low posterior hairline**. - Other classic features include **gonadal dysgenesis**, **cardiac anomalies** (e.g., coarctation of the aorta), and **renal anomalies**. - **Occurs only in females** due to the chromosomal abnormality. *Edwards syndrome* - **Edwards syndrome** (Trisomy 18) is characterized by severe developmental delays, a **rocker-bottom feet deformity**, **micrognathia**, and **clenched hands with overlapping fingers**. - **Webbed neck** and **short stature** are not primary distinguishing features of Edwards syndrome. *Patau syndrome* - **Patau syndrome** (Trisomy 13) is associated with severe midline defects, including **cleft lip and palate**, **polydactyly**, **microphthalmia**, and **holoprosencephaly**. - It does not typically present with a **webbed neck** or a **low posterior hairline**. *Down syndrome* - **Down syndrome** (Trisomy 21) is typically characterized by **upslanting palpebral fissures**, a **single palmar crease**, **intellectual disability**, and **cardiac defects**. - While **short stature** can be present, the classic combination of a **webbed neck** and **low posterior hairline** is not characteristic of Down syndrome. *Noonan syndrome* - **Noonan syndrome** shares phenotypic similarities with Turner syndrome, including **webbed neck**, **short stature**, and **cardiac defects** (especially pulmonary stenosis). - However, it occurs in **both males and females** with a **normal karyotype** and is caused by mutations in genes of the RAS-MAPK pathway. - Key differentiating features include **pectus excavatum**, **cryptorchidism in males**, and the absence of gonadal dysgenesis.
Question 7: Which investigation is the gold standard for diagnosing Edwards syndrome?
- A. Karyotype (Correct Answer)
- B. MLPA
- C. Microarray
- D. FISH
Explanation: ***Karyotype*** - A **karyotype** is considered the **gold standard** for diagnosing chromosomal abnormalities like **Edwards syndrome** (Trisomy 18) because it allows for the visualization and analysis of all 46 chromosomes [1]. - It can detect changes in chromosome number (aneuploidy) and large structural rearrangements, directly confirming the presence of an extra chromosome 18 [2]. *MLPA (Multiplex Ligation-dependent Probe Amplification)* - **MLPA** is a molecular technique used to detect **copy number variations** for specific targeted regions but does not provide a comprehensive view of the entire karyotype. - While it can detect trisomies, it is generally used for specific gene deletions or duplications and is not the first-line diagnostic method for whole chromosome aneuploidies like Edwards syndrome. *Microarray (Chromosomal Microarray Analysis)* - **Microarray** is a high-resolution method that can detect smaller deletions and duplications (microdeletions/microduplications) unidentifiable by traditional karyotyping. - However, for whole chromosome trisomies, a **karyotype** remains the gold standard as it directly visualizes the extra chromosome rather than inferring its presence through copy number changes of multiple probes [3]. *FISH (Fluorescence In Situ Hybridization)* - **FISH** is a targeted technique that uses fluorescent probes to detect specific chromosomal regions or whole chromosomes [3]. - While useful for rapid detection of common aneuploidies or specific translocations, it requires prior suspicion of a particular chromosomal abnormality and does not provide a comprehensive global view of all chromosomes like a traditional **karyotype** [3]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Genetic Disorders, pp. 167-168. [2] 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. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Genetic Disorders, pp. 186-187.
Question 8: What term describes a chromosomal number that is an exact multiple of 23?
- A. Euploidy (Correct Answer)
- B. Aneuploidy
- C. Mosaicism
- D. Trisomy
Explanation: ***Euploidy*** - Euploidy refers to the condition where the **chromosomal number is an exact multiple of 23**, indicating a complete set of chromosomes. - This condition represents the normal state for organisms and includes multiples like **diploidy (2n)** and **triploidy (3n)**. *Aneuploidy* - Aneuploidy is an **abnormal chromosomal number** that is not a complete multiple of 23, leading to conditions like **trisomy** or **monosomy** [1]. - It typically results in **genetic disorders** such as Down syndrome (Trisomy 21) due to the presence of an extra chromosome [1]. *Trisomy* - Trisomy specifically refers to the presence of an **extra chromosome** in a pair, resulting in a total of 47 chromosomes instead of the normal 46 [1]. - It is a specific type of **aneuploidy**, making it not a complete multiple of 23 in the context discussed [1]. *Mosaicism* - Mosaicism describes a situation where an individual has **two or more genetically different cell lines**, leading to a mix of normal and abnormal cells [1]. - It does not inherently correspond to an **exact multiple** of chromosome sets, thus not applicable here [1]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Genetic Disorders, pp. 168-169.
Question 9: Number of chromosomes in Klinefelter syndrome:
- A. 44
- B. 46
- C. 47 (Correct Answer)
- D. 45
Explanation: ***47*** - **Klinefelter syndrome** is a genetic condition in males characterized by the presence of an extra X chromosome, resulting in a **47, XXY karyotype** [1]. - This additional chromosome increases the total count from the typical 46 to **47** [1]. *44* - A count of 44 chromosomes would indicate either a severe **aneuploidy** or a **haploid** state, which is not compatible with human life in a full somatic cell. - Normal human somatic cells contain 46 chromosomes (2n). *46* - A count of 46 chromosomes represents the **normal diploid number** for human somatic cells (46, XX for females and 46, XY for males). - This count would signify a genetically typical individual, not someone with Klinefelter syndrome. *45* - A count of 45 chromosomes typically indicates a **monosomy**, such as **Turner syndrome** (45, X) in females, where one sex chromosome is missing. - This is a different chromosomal abnormality from Klinefelter syndrome, which involves an extra chromosome. **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. 92-93.
Question 10: Which of the following conditions is characterized by the presence of telangiectasia?
- A. Hereditary hemorrhagic telangiectasia (Correct Answer)
- B. Telangiectasia due to systemic sclerosis
- C. Telangiectasia due to rosacea
- D. Acquired telangiectasia due to sun exposure
Explanation: ***Hereditary hemorrhagic telangiectasia*** - This condition, also known as **Osler-Weber-Rendu disease**, is a **genetic disorder** resulting in abnormal blood vessel formation, leading to **telangiectasias** and arteriovenous malformations that can cause significant bleeding. - Key diagnostic criteria include spontaneous recurrent nosebleeds, multiple mucocutaneous telangiectasias, visceral organ involvement (e.g., pulmonary, hepatic, cerebral AVMs), and a family history. *Telangiectasia due to systemic sclerosis* - While telangiectasias can be a feature of **systemic sclerosis** (especially the limited cutaneous form, **CREST syndrome**), they are typically localized and are not the primary defining characteristic of the disease. - Systemic sclerosis is primarily characterized by **fibrosis of skin and internal organs**, and the telangiectasias are a secondary manifestation, not the fundamental underpinning of the condition as in HHT. *Telangiectasia due to rosacea* - **Rosacea** is a chronic inflammatory skin condition characterized by facial erythema, papules, pustules, and **telangiectasias**, particularly on the cheeks and nose. - However, rosacea-associated telangiectasias are localized to the face and are part of a broader inflammatory dermatological process, distinct from the systemic vascular abnormalities seen in HHT. *Acquired telangiectasia due to sun exposure* - **Sun exposure** can indeed cause **telangiectasias**, particularly on sun-damaged skin, due to chronic photodamage to dermal blood vessels. - These are generally localized, non-syndromic, and a result of environmental factors rather than a systemic or inherited disorder as seen in hereditary hemorrhagic telangiectasia.
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