Genetics and Disease — MCQs

Genetics and Disease Indian Medical PG Practice Questions and MCQs

Question 301: Which of the following statements about Wilson's disease is false?

A. Autosomal recessive
B. Serum ceruloplasmin level < 20 mg/dl
C. Urinary copper excretion < 100 micrograms/day (Correct Answer)
D. Zinc acetate is used as maintenance therapy

Explanation: ***Urinary copper excretion < 100 micrograms/day*** - A definitive diagnostic criterion for Wilson's disease is an **elevated 24-hour urinary copper excretion**, typically **greater than 100 µg/day** (or occasionally 40-100 μg/day in symptomatic patients). - Therefore, a value *less than 100 µg/day* would be considered a normal finding and would indicate that Wilson's disease is unlikely, making this statement false in the context of diagnosing the disease. *Autosomal recessive* - Wilson's disease is inherited in an **autosomal recessive pattern**, meaning an individual must inherit two copies of the mutated *ATP7B* gene (one from each parent) to develop the disease. - This characteristic inheritance pattern is fundamental to understanding the genetic basis of the disorder. *Serum ceruloplasmin level < 20 mg/dl* - **Low serum ceruloplasmin** (typically < 20 mg/dL) is a hallmark of Wilson's disease, as ceruloplasmin is the major copper-carrying protein in the blood, and its synthesis is impaired. - This low level indicates defective copper metabolism and transport, leading to copper accumulation. *Zinc acetate is used as maintenance therapy* - **Zinc acetate** (e.g., Galzin) is a commonly used maintenance therapy for Wilson's disease. - It works by inducing **metallothionein** in enterocytes, which sequesters dietary copper and prevents its absorption, thereby promoting fecal copper excretion.

Question 302: Which of the following laboratory findings is the MOST characteristic of Wilson's disease?

A. Elevated serum copper
B. Low serum copper
C. Increased urinary copper excretion (Correct Answer)
D. Low ceruloplasmin

Explanation: ***Low ceruloplasmin and high urinary copper*** - In Wilson's disease, there is decreased **ceruloplasmin** due to impaired copper metabolism, leading to low levels in the serum [1]. - The condition results in **increased urinary copper excretion**, which is a hallmark feature and confirms the diagnosis [2]. *Low urinary copper* - Wilson's disease presents with **high urinary copper** levels due to excessive copper being expelled by the kidneys. - **Low urinary copper** would suggest a different condition, such as **Chronic liver disease** or **renal tubular disorders**. *High ceruloplasmin* - Patients with Wilson's disease have **low ceruloplasmin levels** rather than high, indicating ineffective copper transport [1]. - **High ceruloplasmin** levels are typically associated with conditions like **inflammation** or **pregnancy** rather than Wilson's disease. *Low serum copper* - In Wilson's disease, serum copper levels are typically **normal or elevated**, not low. - The primary defect is in the transport of copper, resulting in accumulation in tissues, not a deficiency in serum levels [1]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Liver and Gallbladder, pp. 855-856. [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. 132-133.

Question 303: Which of the following is NOT an X-linked disease?

A. Hemophilia A
B. Duchenne Muscular Dystrophy
C. Cystic Fibrosis (Correct Answer)
D. Color Blindness

Explanation: ***DE*** - This oes not correspond to recognized **X-linked diseases**, making it the correct choice of exception. - X-linked diseases primarily include **Duchenne muscular dystrophy** [1] and **hemophilia**, which are not found in this option. *AB* - This an represent **conditions like hemophilia**, which are clearly X-linked. - Many X-linked diseases affect males more severely due to the single X chromosome. *BC* - Similar to AB, this could allude to X-linked conditions, such as **hemophilia A or B**. - X-linked inheritance patterns result in a higher prevalence in males compared to females. *CA* - May also relate to **X-linked disorders**, including **color blindness** or **Duchenne muscular dystrophy** [1]. - These diseases follow a characteristic pattern of inheritance tied to the X chromosome [1].

Question 304: Genetic anticipation is characteristic of:

A. Myotonic dystrophy (Correct Answer)
B. Duchenne muscular dystrophy
C. Emery-Dreifuss muscular dystrophy
D. Beckers muscular dystrophy

Explanation: ### Myotonic dystrophy - **Genetic anticipation** is a hallmark of myotonic dystrophy, where the disease worsens and appears earlier in successive generations due to expansion of **CTG trinucleotide repeats**. - Symptoms include **myotonia** (delayed muscle relaxation), muscle wasting, cataracts, and cardiac conduction defects. ### Duchenne muscular dystrophy - This is an **X-linked recessive** disorder caused by mutations in the **dystrophin gene**, leading to progressive muscle degeneration [1], [2]. - It does not demonstrate genetic anticipation; the severity and age of onset are generally consistent within affected families. ### Emery-Dreifuss muscular dystrophy - Characterized by a classic triad of **humero-peroneal muscle weakness**, **contractures** (especially of elbows, ankles, and neck), and **cardiac conduction abnormalities**. - It is typically inherited in an X-linked, autosomal dominant, or autosomal recessive manner, but does not involve genetic anticipation. ### Becker muscular dystrophy - A milder form of muscular dystrophy than Duchenne, also caused by mutations in the **dystrophin gene**, but results in a partially functional protein. - While it is a progressive muscle weakness disorder, it does not exhibit the phenomenon of genetic anticipation.

Question 305: Which one of the following disorders is not X-linked recessive?

A. Lesch-Nyhan syndrome
B. Hunter syndrome
C. Charcot-Marie-Tooth disease (Correct Answer)
D. Fragile-X syndrome

Explanation: **Charcot-Marie-Tooth disease** - Charcot-Marie-Tooth disease encompasses a group of **hereditary neuropathies** that are most commonly inherited in an **autosomal dominant** pattern, though autosomal recessive and X-linked forms exist, but the dominant form is the most prevalent. - Its diverse genetic basis means it's not exclusively an X-linked recessive disorder. *Lesch-Nyhan syndrome* - This is an **X-linked recessive** disorder caused by a deficiency of the enzyme **hypoxanthine-guanine phosphoribosyltransferase (HGPRT)**. - It is characterized by **hyperuricemia**, neurological dysfunction, and self-mutilating behavior. *Hunter syndrome* - Hunter syndrome (Mucopolysaccharidosis Type II) is an **X-linked recessive** lysosomal storage disorder [1]. - It results from a deficiency of the enzyme **iduronate-2-sulfatase** [1]. *Fragile-X syndrome* - Fragile-X syndrome is an **X-linked disorder** and is the most common inherited cause of intellectual disability. - It is caused by an expansion of a **CGG trinucleotide repeat** in the FMR1 gene.

Question 306: A middle-aged woman with a history of backache who underwent a Schober test and tested positive, and who also has hyperpigmented nose and ears, is most likely diagnosed with:

A. Ankylosing spondylitis
B. Degenerative disc disease
C. Ochronosis (Correct Answer)
D. Fluorosis

Explanation: ***Ochronosis*** - **Hyperpigmentation of the nose and ears** (due to homogentisic acid accumulation) along with **backache** and a positive **Schober test** (indicating spinal inflexibility from ochronotic arthropathy) are classic features of ochronosis. - This inherited disorder results from a deficiency of **homogentisic acid oxidase**, leading to the accumulation of homogentisic acid. *Ankylosing spondylitis* - While **backache** and a positive **Schober test** (indicating axial skeleton involvement) are characteristic of ankylosing spondylitis, it does not typically present with **hyperpigmented nose and ears**. - **HLA-B27 positivity** and inflammatory back pain improving with activity are key differentiating features not mentioned. *Degenerative disc disease* - This condition is characterized by **chronic backache** due to age-related changes in the intervertebral discs but does not cause **hyperpigmentation of the nose and ears**. - A **positive Schober test** is less specific for degenerative disc disease and is more indicative of widespread spinal stiffness. *Fluorosis* - While severe fluorosis can lead to **skeletal changes** and pain mimicking arthritis, it is primarily associated with **dental mottling** and does not cause characteristic hyperpigmentation of the nose and ears. - มัน usually results from excessive fluoride intake, often from contaminated drinking water.

Question 307: Which disorder is associated with NARP syndrome, characterized by neuropathy, ataxia, and retinitis pigmentosa?

A. Mitochondrial function disorder (Correct Answer)
B. Glycogen storage disorder
C. Lysosomal storage disorder
D. Lipid storage disorder

Explanation: ***Mitochondrial function disorder*** - NARP syndrome (Neurogenic weakness, Ataxia, Retinitis Pigmentosa) is caused by a specific point mutation in the **MT-ATP6 gene**, which encodes a subunit of the mitochondrial ATP synthase [1]. - This mutation leads to impaired mitochondrial energy production, affecting tissues with high energy demands, such as the **nervous system** and retina [1]. *Glycogen storage disorder* - These disorders involve defects in enzymes responsible for **glycogen synthesis or degradation**, leading to abnormal glycogen accumulation in tissues [1]. - While they can cause muscle weakness and neurological symptoms, the specific constellation of **neuropathy, ataxia, and retinitis pigmentosa** is not characteristic of glycogenoses. *Lysosomal storage disorder* - These conditions result from deficiencies in lysosomal enzymes, causing the accumulation of **undigested macromolecules** within lysosomes. - Symptoms vary widely but typically involve progressive neurological degeneration, organomegaly, and skeletal abnormalities, without the classic NARP presentation. *Lipid storage disorder* - These disorders are characterized by the accumulation of **specific lipids** due to enzyme deficiencies involved in lipid metabolism. - Examples include Gaucher disease and Niemann-Pick disease, which involve different clinical manifestations such as hepatosplenomegaly, bone crises, and various neurological issues, distinct from NARP syndrome.

Question 308: Which of the following is not a major criterion for diagnosing Marfan syndrome?

A. Dilatation of the ascending aorta
B. Dural ectasia
C. Ectopia lentis
D. Striae over the buttocks (Correct Answer)

Explanation: Striae over the buttocks - While striae (stretch marks) can be common in individuals with Marfan syndrome due to connective tissue fragility, they are considered a minor criterion rather than a major one based on the Ghent nosology. - Major criteria are defined by their higher diagnostic specificity and clinical significance in identifying Marfan syndrome. Ectopia lentis - Ectopia lentis (dislocation of the ocular lens) is a major diagnostic criterion for Marfan syndrome and is highly specific to the condition. - It results from the weakness of the suspensory ligaments of the lens due to fibrillin-1 deficiency. Dilatation of the ascending aorta - Aortic root dilatation and aortic dissection are critical cardiovascular manifestations and major diagnostic criteria for Marfan syndrome [1]. - These reflect the systemic connective tissue defect affecting the integrity of the aortic wall and are associated with significant morbidity and mortality [1]. Dural ectasia - Dural ectasia, which is the widening of the dural sac due to weakening of connective tissue, is a major criterion for the diagnosis of Marfan syndrome when observed on imaging studies. - It often occurs in the lumbosacral region and can cause neurological symptoms.

Question 309: Which of the following is a feature of Ehlers-Danlos syndrome?

A. Achalasia
B. Kyphoscoliosis
C. Joint hypermobility (Correct Answer)
D. Dermatosparaxis

Explanation: ***Pectus excavatum*** - This condition is characterized by a **depression of the sternum**, leading to a sunken chest appearance, and is least commonly associated with Ehlers-Danlos syndrome (EDS). - Other forms of EDS may present with more notable **joint hypermobility** and skin elasticity issues, rather than pectus excavatum [1]. *Kyphoscoliosis* - This is a common complication in certain types of Ehlers-Danlos syndrome, particularly affecting the spine's curvature [1]. - It is associated with **joint hypermobility** and can lead to significant postural abnormalities [1]. *Achalasia* - While achalasia can occur in EDS, it is not a typical or common association. - This esophageal motility disorder primarily affects **swallowing** due to a failure of the lower esophageal sphincter to relax. *Dermatosparaxis* - This form of EDS specifically features **skin fragility** and tearing with minimal trauma, indicating a significant association with the syndrome [1]. - It is characterized by **excessively fragile skin** and is directly linked to the pathogenic mechanisms of EDS [1].

Question 310: What is the most characteristic finding in familial adenomatous polyposis (FAP)?

A. Predominantly affects males
B. Autosomal dominant inheritance (Correct Answer)
C. If not treated, FAP has a very high risk of progressing to malignancy.
D. Males and females are affected equally

Explanation: ***Familial adenomatous polyposis affects both males and females equally.*** - Familial adenomatous polyposis (FAP) follows an **autosomal dominant inheritance pattern**, therefore affecting both genders. - It typically presents with **hundreds to thousands of adenomatous polyps** in the colon, leading to a significant risk for colon cancer if untreated [1]. *If not treated, it progresses to malignancy in nearly all cases.* - While untreated FAP has a high risk for colorectal cancer, it does not mean **all cases** progress to malignancy; some may be managed effectively. - Regular screening and prophylactic surgery can significantly **reduce** the malignant potential associated with the condition [1]. *Males and females are affected equally.* - While FAP affects males and females, the tendency for development of certain cancers may vary; stating it affects them **equally** could be misleading due to varying cancer risks. - The inheritance and clinical implications do not make a distinction based on gender despite equal prevalence. *Autosomal dominant inheritance.* - This statement about inheritance is indeed **true**, but it is not the correct statement regarding FAP's equality in affecting genders. - The **mutated APC gene** is responsible for FAP, leading to the widespread formation of polyps and the risk of colon cancer [1].

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Principles of Medical Genetics

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Genetic Testing and Counseling

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Single Gene Disorders

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Chromosomal Disorders

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Mitochondrial Diseases

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Pharmacogenomics

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Cancer Genetics

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Genetics of Common Diseases

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Epigenetics and Disease

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Genetic Basis of Developmental Disorders

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Ethical Issues in Medical Genetics

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Gene Therapy and Precision Medicine

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