Genetics in Dermatology — MCQs

10 questions

Disputed maternity can be solved by using the following tests, EXCEPT:

An affected male does not have affected children but an affected female always has affected children. Type of inheritance?

Which of the following is used to detect abnormal gene sequences EXCEPT?

A patient has multiple meningiomas, acoustic neuroma and hyperpigmented skin lesions; most likely diagnosis is –

Baby born with membrane around him at the time of birth. Which of the following conditions is depicted?

A 5-month-old child presented to the dermatology OPD with dryness along with white, fine scales on most parts of the body with sparing of face. The child was born at 39 weeks gestation by spontaneous vaginal delivery outside the hospital. On examination, fine, white scales were observed predominantly on the extensor surfaces of the limbs along with characteristic hyperlinearity of palms and accentuation of skin markings. Which of the following genes is most likely defective in the above condition:

All are true about this lesion seen in a child with epilepsy except:

A patient presents with the skin finding shown in the image. Identify the most likely diagnosis for this lesion.

A 6-year-old child born to consanguinity has pallor and intolerance to sunlight. His urine was exposed to Wood's light. Probable diagnosis is:

Q10

Lines of Blaschko are related to?

Genetics in Dermatology Indian Medical PG Practice Questions and MCQs

Question 1: Disputed maternity can be solved by using the following tests, EXCEPT:

A. Blood grouping
B. HLA typing
C. DNA fingerprinting
D. Precipitin test (Correct Answer)

Explanation: ***Precipitin test*** - The **precipitin test** is used to determine the origin of a **blood sample**, specifically whether it is **human or animal blood**, by detecting species-specific proteins. It is not used for assessing maternity. - This test is primarily employed in **forensic serology** to differentiate between blood from different animal species, making it irrelevant for paternity or maternity disputes. *Blood grouping* - **Blood grouping** (e.g., ABO and Rh systems) can be used to **exclude paternity or maternity** by comparing the blood types of the child, mother, and alleged father. - If the child's blood type is incompatible with the alleged parents based on Mendelian inheritance, one or both can be excluded. *HLA typing* - **HLA typing** (Human Leukocyte Antigen) is a more powerful genetic marker system than ABO/Rh for determining paternity or maternity. - It involves analyzing highly polymorphic genes on chromosome 6 that encode cell surface proteins, providing a more definitive means of **inclusion or exclusion**. *DNA fingerprinting* - **DNA fingerprinting** (also known as **DNA profiling**) is the **most accurate and widely accepted method** for resolving paternity and maternity disputes. - It analyzes highly variable regions of DNA unique to each individual, providing a statistically strong basis for **inclusion or exclusion** by comparing genetic profiles.

Question 2: An affected male does not have affected children but an affected female always has affected children. Type of inheritance?

A. Autosomal recessive
B. Mitochondrial (Correct Answer)
C. X linked recessive
D. X linked dominant

Explanation: ***Correct Option: Mitochondrial*** - This pattern describes **mitochondrial inheritance**, where all children of an **affected mother** inherit the condition because mitochondria are exclusively inherited from the ovum (maternal inheritance). - An **affected father** cannot pass on the condition to his children, as sperm contribute only nuclear DNA and essentially no mitochondria. - This is the **only inheritance pattern** where an affected male has no affected children while an affected female has all children affected. *Incorrect Option: Autosomal recessive* - This pattern would typically show affected individuals having unaffected parents (who are carriers) and both males and females being affected in equal proportions. - It does not explain the complete absence of transmission from an affected father or universal transmission from an affected mother. - An affected individual could have unaffected children if their partner is not a carrier. *Incorrect Option: X linked recessive* - In **X-linked recessive inheritance**, affected males cannot pass the trait to their sons, but all their daughters would be carriers (not affected). - An affected mother would pass the trait to all her sons (affected) and make all her daughters carriers (not affected), which does not match the described pattern of all children being affected. *Incorrect Option: X linked dominant* - In **X-linked dominant inheritance**, an affected father passes the trait to all his daughters but none of his sons (contradicts "no affected children"). - An affected mother has a 50% chance of passing the trait to **each child**, which is inconsistent with all children of an affected female being affected.

Question 3: Which of the following is used to detect abnormal gene sequences EXCEPT?

A. RFLP analysis
B. Pyrosequencing
C. Flow cytometry (Correct Answer)
D. FISH

Explanation: ***Flow cytometry*** - **Flow cytometry** is primarily used to analyze **cell populations** based on their physical and biochemical characteristics (e.g., size, granularity, and protein expression) by passing them single file through a laser beam, not for direct gene sequencing. - It detects and quantifies cells labeled with **fluorescent antibodies**, making it useful for immunophenotyping, cell sorting, and DNA content analysis, but not for identifying specific gene sequences or mutations. *RFLP analysis* - **Restriction fragment length polymorphism (RFLP) analysis** detects variations in **DNA sequences** by using **restriction enzymes** to cut DNA at specific sites. - Differences in fragment lengths indicate **polymorphisms** or **mutations** within the recognition sites, thereby identifying abnormal gene sequences. *Pyrosequencing* - **Pyrosequencing** is a method of **DNA sequencing** that determines the sequence of nucleotides by detecting the release of pyrophosphate during DNA synthesis. - It is used to identify **single nucleotide polymorphisms (SNPs)** and **short genetic variations**, making it suitable for detecting abnormal gene sequences. *FISH* - **Fluorescence in situ hybridization (FISH)** uses **fluorescently labeled DNA probes** that bind to specific complementary **DNA sequences** on chromosomes. - It is a powerful cytogenetic technique for detecting **chromosomal abnormalities**, such as deletions, translocations, and amplifications, thereby identifying abnormal gene sequences.

Question 4: A patient has multiple meningiomas, acoustic neuroma and hyperpigmented skin lesions; most likely diagnosis is –

A. Neurofibromatosis (Correct Answer)
B. Von Hippel lindau disease
C. Sturge weber syndrome
D. Tuberous sclerosis

Explanation: ***Neurofibromatosis*** - The combination of **multiple meningiomas**, **acoustic neuroma** (specifically bilateral in NF2) [1], and **hyperpigmented skin lesions** (cafe-au-lait spots in NF1, or multiple cutaneous neurofibromas) is highly characteristic of neurofibromatosis. - This presentation suggests either **Neurofibromatosis type 1 (NF1)** with meningiomas (less common but possible) or, more strongly, **Neurofibromatosis type 2 (NF2)** due to the bilateral acoustic neuromas and the presence of meningiomas, with hyperpigmentation being a variable feature [1]. *Von Hippel-Lindau disease* - This disorder is characterized by **hemangioblastomas** of the retina and central nervous system, **renal cell carcinoma**, and **pheochromocytomas**. - It does not typically involve meningiomas, acoustic neuromas, or hyperpigmented skin lesions. *Sturge-Weber syndrome* - This is a neurocutaneous disorder featuring a **port-wine stain (facial nevus flammeus)**, leptomeningeal angioma, and **glaucoma**. - The clinical picture of meningiomas, acoustic neuroma, and hyperpigmented skin lesions does not align with Sturge-Weber syndrome. *Tuberous sclerosis* - This condition is characterized by the growth of numerous **benign tumors in many different organs**, including the brain (tubers, subependymal giant cell astrocytomas), skin (facial angiofibromas, shagreen patches, ash-leaf spots), kidneys (angiomyolipomas), and heart (rhabdomyomas). - While it has **skin lesions** and **brain tumors**, these are distinct from meningiomas and acoustic neuromas, which are not typical features.

Question 5: Baby born with membrane around him at the time of birth. Which of the following conditions is depicted?

A. X-linked ichthyosis (steroid sulfatase deficiency)
B. Generalized hyperkeratosis (thickened skin)
C. Ichthyosis vulgaris (dry, scaly skin)
D. Lamellar ichthyosis (collodion membrane at birth) (Correct Answer)

Explanation: ***Lamellar ichthyosis (collodion membrane at birth)*** - This condition is characterized by a "collodion membrane" at birth, which is a **tight, shiny, parchment-like membrane** that covers the entire body. - The membrane typically **sheds within weeks**, revealing underlying scaling and erythema characteristic of lamellar ichthyosis. *X-linked ichthyosis (steroid sulfatase deficiency)* - Marked by **dark brown, adherent scales**, primarily affecting the neck, trunk, and extensor surfaces. - It usually becomes apparent **several weeks or months after birth** and is not typically associated with a collodion membrane. *Generalized hyperkeratosis (thickened skin)* - This is a general term for **thickening of the outermost layer of the epidermis** and is a feature of many ichthyoses, not a specific condition with a "membrane at birth." - It describes a **symptom** rather than a primary diagnosis presenting with a specific birth membrane. *Ichthyosis vulgaris (dry, scaly skin)* - Presents with **fine, white scaling**, most prominent on the extensor surfaces of the limbs, but it **rarely appears at birth**. - It is typically **mild** and often worsens in dry, cold weather, lacking the characteristic "membrane around him" at birth.

Question 6: A 5-month-old child presented to the dermatology OPD with dryness along with white, fine scales on most parts of the body with sparing of face. The child was born at 39 weeks gestation by spontaneous vaginal delivery outside the hospital. On examination, fine, white scales were observed predominantly on the extensor surfaces of the limbs along with characteristic hyperlinearity of palms and accentuation of skin markings. Which of the following genes is most likely defective in the above condition:

A. Filaggrin (Correct Answer)
B. Desmoglein
C. Plakophilin
D. Plakoglobin

Explanation: ***Filaggrin*** - The clinical description of **fine, white scales**, **facial sparing**, **extensor surface involvement**, and **palmar hyperlinearity** is classic for **ichthyosis vulgaris**, the most common inherited disorder of keratinization. - **Filaggrin (FLG)** gene mutations are the most common cause of ichthyosis vulgaris, leading to impaired formation of the skin barrier and loss of natural moisturizing factor. - Typically presents between 3-12 months of age with xerosis and fine scaling. - Key features include **facial sparing**, **flexural sparing**, and **prominent palmar/plantar markings**. *Desmoglein* - **Desmoglein 1** and **Desmoglein 3** are desmosomal cadherins associated with **pemphigus** (autoimmune blistering disorder). - Desmoglein mutations do not cause ichthyotic scaling disorders. - The clinical presentation of fine scaling with facial sparing is not consistent with pemphigus or other desmoglein-related conditions. *Plakophilin* - **Plakophilin-1** mutations cause **ectodermal dysplasia-skin fragility syndrome**, characterized by skin erosions, blistering, alopecia, and nail dystrophy. - Does not present with generalized dry scaling or the pattern described in this case. - Skin fragility and erosions are the hallmark, not ichthyosis. *Plakoglobin* - **Plakoglobin (JUP gene)** mutations cause **Naxos disease**, featuring the triad of arrhythmogenic right ventricular cardiomyopathy, woolly hair, and palmoplantar keratoderma. - While palmoplantar involvement occurs, it is a focal keratoderma, not generalized fine scaling with facial sparing. - Cardiac manifestations are the most serious feature of this condition.

Question 7: All are true about this lesion seen in a child with epilepsy except:

A. Collagenoma
B. Minor criteria for diagnosis (Correct Answer)
C. Peau d'orange appearance
D. Predominantly seen over trunk

Explanation: ***Minor criteria for diagnosis*** - The presented lesion is a **Shagreen patch**, which is considered a **major diagnostic criterion** for **Tuberous Sclerosis Complex (TSC)**, not a minor one. - A definitive diagnosis of TSC requires two major criteria or one major and two minor criteria. *Collagenoma* - A Shagreen patch is a type of dermal **collagenoma**, characterized by an overgrowth of connective tissue, primarily collagen. - These lesions often feel like **roughened or leathery plaques** on the skin. *Peau d'orange appearance* - The Shagreen patch is often described as having a **'peau d'orange'** or orange peel-like texture due to its irregular surface. - This characteristic texture helps in its clinical identification. *Predominantly seen over trunk* - Shagreen patches are typically located on the **trunk**, especially in the lumbosacral region, as seen in the image. - They are one of the distinctive cutaneous manifestations of TSC.

Question 8: A patient presents with the skin finding shown in the image. Identify the most likely diagnosis for this lesion.

A. Vitiligo
B. Contact leukoderma
C. Piebaldism (Correct Answer)
D. Albinism

Explanation: ***Piebaldism*** - The image shows a **localized patch of depigmentation** on the forehead, characteristic of **piebaldism**. - **Piebaldism** is a rare, congenital autosomal dominant disorder caused by a defect in melanocyte development and migration, resulting in stable, well-demarcated depigmented areas, often with a **white forelock**. *Vitiligo* - **Vitiligo** typically presents as **progressive, acquired macules and patches of depigmentation** that often enlarge over time. - While it can appear on the face, the sharply demarcated, congenital appearance seen here is more consistent with piebaldism. *Contact leukoderma* - **Contact leukoderma** is an **acquired depigmentation** resulting from exposure to chemicals (e.g., rubber, phenols). - It would usually present in areas of direct contact, and the congenital nature of the lesion in the image rules this out. *Albinism* - **Albinism** is a **generalized hypopigmentation** affecting the skin, hair, and eyes due to a defect in melanin production. - The image shows a localized patch of depigmentation, not a widespread lack of pigment characteristic of albinism.

Question 9: A 6-year-old child born to consanguinity has pallor and intolerance to sunlight. His urine was exposed to Wood's light. Probable diagnosis is:

A. SLE
B. Xeroderma pigmentosum
C. Gunther disease (Correct Answer)
D. Bloom syndrome

Explanation: ***Gunther disease*** - The combination of **pallor**, **intolerance to sunlight** (photosensitivity), **consanguinity**, and particularly the **red fluorescence of urine under Wood's light** (due to increased uroporphyrins and coproporphyrins) is highly characteristic of **congenital erythropoietic porphyria (CEP)**, also known as Gunther disease. - This is an **autosomal recessive** disorder of heme synthesis, leading to accumulation of porphyrin precursors. Affected individuals often have **erythrodontia** (reddish-brown discoloration of teeth), severe **anemia**, and **hemolysis**, alongside marked photosensitivity. *SLE* - **Systemic lupus erythematosus (SLE)** can cause **photosensitivity** and **pallor (due to anemia)**, but it is an autoimmune disease, not an inborn error of metabolism. - It does not typically present with red fluorescent urine under Wood's light, which is a specific finding for porphyrias. *Xeroderma pigmentosum* - This is a rare **autosomal recessive** genetic disorder characterized by extreme **photosensitivity** and a high risk of skin cancers due to a defect in DNA repair mechanisms. - While it causes severe photosensitivity, it does not involve abnormalities in porphyrin metabolism or lead to red fluorescent urine. *Bloom syndrome* - **Bloom syndrome** is a rare **autosomal recessive** genetic disorder characterized by **photosensitivity**, **short stature**, a **distinctive facial appearance**, and an increased risk of cancer. - It does not involve porphyrin metabolism or result in red fluorescent urine under Wood's light.

Question 10: Lines of Blaschko are related to?

A. Keratinocytes (Correct Answer)
B. Blood vessels
C. Nerves
D. Bones

Explanation: ***Keratinocytes*** - **Lines of Blaschko** represent the migratory pathways of embryonic cells, primarily **keratinocytes**, in the skin. - These lines are not visible under normal conditions but become apparent in various **genetic skin disorders** where abnormal cells follow these specific patterns. *Blood vessels* - While blood vessels are extensively present in the skin, they do not follow the specific **migratory patterns** described by the Lines of Blaschko. - Their arrangement is more related to **vascular networks** and anatomical supply rather than embryonic cell migration. *Nerves* - **Nerves** in the skin have specific distributions, often following dermatomal patterns, which are distinct from the **Lines of Blaschko**. - Nerve distribution is related to their segmental origin from the **spinal cord**, not the migratory paths of epidermal cells. *Bones* - **Bones** are part of the skeletal system and are not found in the skin, making them unrelated to the **Lines of Blaschko**. - These lines describe epidermal cell migration, which is a feature of the **integumentary system**.

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