Diagnostic approaches — MCQs

10 questions

A deficiency in which of the following lysosomal enzymes is inherited in a pattern similar to a deficiency of iduronate sulfatase (Hunter syndrome)?

A 37-year-old primigravid woman comes to the physician at 13 weeks' gestation for a prenatal visit. She feels well. Her only medication is folic acid. Vital signs are within normal limits. Pelvic examination shows a uterus consistent in size with a 13-week gestation. Ultrasonography shows a nuchal translucency above the 99th percentile. Maternal serum pregnancy-associated plasma protein A is decreased and human chorionic gonadotropin concentrations are elevated to 2 times the median level. Which of the following is most likely to confirm the diagnosis?

A 4-month-old male infant is brought in because he rejects food and is losing weight. He had several upper respiratory tract infections during the last 2 months. Upon examination, hepatosplenomegaly is noted, as well as mild hypotonia. During the next few weeks, hepatosplenomegaly progresses, the boy fails to thrive, and he continues to reject food. He has a blood pressure of 100/70 mm Hg and heart rate of 84/min. Blood tests show pancytopenia and elevated levels of transaminases. Slit lamp examination shows bilateral cherry-red spots on the macula. Chest X-ray shows a reticulonodular pattern and calcified nodules. Biopsy of the liver shows foamy histiocytes. What is the most likely diagnosis?

A 26-year-old woman presents to a physician for genetic counseling, because she is worried about trying to have a child. Specifically, she had 2 siblings that died young from a lysosomal storage disorder and is afraid that her own children will have the same disorder. Her background is Ashkenazi Jewish, but she says that her husband's background is mixed European heritage. Her physician says that since her partner is not of Jewish background, their chance of having a child with Niemann-Pick disease is dramatically decreased. Which of the following genetic principles best explains why there is an increased prevalence of this disease in some populations?

A 3-month-old infant is brought to her pediatrician for a well-child visit. The infant was born to a 22-year-old mother via a spontaneous vaginal delivery at 38 weeks of gestation in her home. She moved to the United States approximately 3 weeks ago from a small village. She reports that her infant had 2 episodes of non-bloody and non-bilious vomiting. The infant's medical history includes eczema and 2 seizure episodes that resolved with benzodiazepines in the emergency department. Physical examination is notable for a musty body odor, eczema, and a fair skin complexion. Which of the following is the best next step in management?

A research study evaluates three siblings with Niemann-Pick disease type C: a 6-year-old with ataxia and vertical supranuclear gaze palsy, a 10-year-old with hepatosplenomegaly and mild cognitive impairment, and a 14-year-old who is asymptomatic. Genetic testing reveals all three carry the same compound heterozygous NPC1 mutations. Fibroblast studies show similar cholesterol esterification defects and filipin staining patterns. Miglustat therapy is available. Evaluate the biological basis for phenotypic variability and optimal treatment allocation.

A 15-year-old boy with Hunter syndrome (MPS II) on weekly enzyme replacement therapy develops IgG antibodies with high neutralizing capacity against idursulfase. His symptoms have worsened over the past 6 months with increasing hepatosplenomegaly and joint stiffness. His brother with the same mutation shows excellent response to ERT without antibody formation. Synthesize an appropriate management plan considering immunologic and genetic factors.

A newborn screening program identifies an infant with deficient β-glucuronidase activity. The infant is currently asymptomatic at 2 weeks of age. The parents are counseled about Sly syndrome (MPS VII) and ask about prognosis. Genetic testing reveals the infant is compound heterozygous with one null allele and one missense mutation (p.P408S) that retains 8% residual enzyme activity. Evaluate the most appropriate management strategy.

A 5-year-old boy with known Gaucher disease type 1 has been on enzyme replacement therapy with imiglucerase for 2 years. His hepatosplenomegaly has decreased and bone pain has improved. However, his mother is concerned about the frequency of IV infusions. Laboratory testing shows he is homozygous for the N370S mutation. Analyze which alternative therapy would be most appropriate and why.

Q10

A 28-year-old man presents with episodes of severe burning pain in his hands and feet, angiokeratomas on his trunk, and decreased sweating. He reports similar symptoms in his maternal uncle who died of renal failure at age 42. Echocardiography shows left ventricular hypertrophy. Serum creatinine is 1.8 mg/dL with proteinuria. Analysis of his lysosomal enzyme profile shows deficiency in one enzyme. What mechanism explains his cardiac manifestations?

Diagnostic approaches US Medical PG Practice Questions and MCQs

Question 1: A deficiency in which of the following lysosomal enzymes is inherited in a pattern similar to a deficiency of iduronate sulfatase (Hunter syndrome)?

A. Sphingomyelinase
B. Glucocerebrosidase
C. Galactocerebrosidase
D. Alpha-L-iduronidase
E. Alpha-galactosidase A (Correct Answer)

Explanation: ***Alpha-galactosidase A*** - A deficiency in **alpha-galactosidase A** causes **Fabry disease**, which, like Hunter syndrome (iduronate sulfatase deficiency), is inherited in an **X-linked recessive** pattern. - Both conditions primarily affect males, with carrier females potentially exhibiting milder symptoms. *Sphingomyelinase* - A deficiency in sphingomyelinase leads to **Niemann-Pick disease types A and B**, which are inherited in an **autosomal recessive** pattern. - This mode of inheritance differs from the X-linked pattern of Hunter syndrome. *Glucocerebrosidase* - A deficiency in glucocerebrosidase causes **Gaucher disease**, inherited in an **autosomal recessive** pattern. - This is a common lysosomal storage disorder, but its inheritance pattern is distinct from X-linked disorders. *Galactocerebrosidase* - A deficiency in galactocerebrosidase causes **Krabbe disease (globoid cell leukodystrophy)**, which is inherited in an **autosomal recessive** pattern. - Krabbe disease is a severe neurodegenerative disorder, but its genetic transmission is not X-linked. *Alpha-L-iduronidase* - A deficiency in **alpha-L-iduronidase** causes **Hurler syndrome (MPS I)**, which is inherited in an **autosomal recessive** pattern. - While both Hunter and Hurler syndromes are mucopolysaccharidoses, their genetic inheritance patterns are different.

Question 2: A 37-year-old primigravid woman comes to the physician at 13 weeks' gestation for a prenatal visit. She feels well. Her only medication is folic acid. Vital signs are within normal limits. Pelvic examination shows a uterus consistent in size with a 13-week gestation. Ultrasonography shows a nuchal translucency above the 99th percentile. Maternal serum pregnancy-associated plasma protein A is decreased and human chorionic gonadotropin concentrations are elevated to 2 times the median level. Which of the following is most likely to confirm the diagnosis?

A. Chorionic villus sampling (Correct Answer)
B. Cell-free DNA testing
C. Triple screening test
D. Amniocentesis
E. Quadruple marker test

Explanation: ***Chorionic villus sampling*** - This procedure can be performed between **10 to 13 weeks of gestation** to obtain fetal cells for genetic analysis, which is within the patient's gestational age. - It provides a definitive diagnosis of **chromosomal abnormalities** by directly sampling placental tissue, which shares the same genetic material as the fetus. *Cell-free DNA testing* - While it has high sensitivity and specificity for various **aneuploidies**, it is a **screening test**, not a diagnostic one. - An abnormal result from cell-free DNA testing still requires **confirmatory diagnostic testing** such as CVS or amniocentesis. *Triple screening test* - This test is typically performed between **15 and 20 weeks of gestation**, which is too late to confirm the findings presented at 13 weeks gestation. - It measures **AFP, hCG, and unconjugated estriol**, and an abnormal result would indicate a need for further diagnostic testing. *Amniocentesis* - This procedure is generally performed later in pregnancy, typically between **15 and 20 weeks gestation**, so it would require waiting several more weeks. - While it provides definitive genetic results, **chorionic villus sampling is preferred at 13 weeks** due to earlier diagnostic potential. *Quadruple marker test* - This test is also performed between **15 and 20 weeks of gestation** and measures **AFP, hCG, unconjugated estriol, and inhibin A**. - It is a **screening test**, similar to the triple screen, and does not provide a definitive diagnosis, requiring further confirmatory testing if abnormal.

Question 3: A 4-month-old male infant is brought in because he rejects food and is losing weight. He had several upper respiratory tract infections during the last 2 months. Upon examination, hepatosplenomegaly is noted, as well as mild hypotonia. During the next few weeks, hepatosplenomegaly progresses, the boy fails to thrive, and he continues to reject food. He has a blood pressure of 100/70 mm Hg and heart rate of 84/min. Blood tests show pancytopenia and elevated levels of transaminases. Slit lamp examination shows bilateral cherry-red spots on the macula. Chest X-ray shows a reticulonodular pattern and calcified nodules. Biopsy of the liver shows foamy histiocytes. What is the most likely diagnosis?

A. Niemann-Pick disease type A (Correct Answer)
B. Tay-Sachs disease
C. Gaucher disease
D. Wolman disease
E. GM1 gangliosidosis

Explanation: ***Niemann-Pick disease type A*** - This presentation of a 4-month-old with **failure to thrive**, progressive **hepatosplenomegaly**, **hypotonia**, recurrent infections, **pancytopenia**, elevated transaminases, **cherry-red spots** on the macula, and **foamy histiocytes** in the liver biopsy is characteristic of Niemann-Pick disease type A. - Niemann-Pick disease type A is a **lysosomal storage disorder** caused by a deficiency of the enzyme **sphingomyelinase**, leading to the accumulation of **sphingomyelin** in various tissues. - The **foamy histiocytes** (lipid-laden macrophages) are a hallmark finding, and the **reticulonodular pattern** on chest X-ray represents pulmonary infiltration. *Incorrect: Tay-Sachs disease* - While Tay-Sachs disease also presents with **cherry-red spots** and progressive neurological deterioration in infancy, it is caused by **hexosaminidase A deficiency**. - Key differences: Tay-Sachs typically does **not** cause **hepatosplenomegaly** or **foamy histiocytes** in the liver; the primary pathology is neuronal accumulation of GM2 ganglioside. - Patients usually present with developmental regression, exaggerated startle response, and hypotonia, but without the prominent organomegaly seen here. *Incorrect: Gaucher disease* - While Gaucher disease also presents with **hepatosplenomegaly** and can cause bone marrow involvement leading to **pancytopenia**, it typically does **not** feature **cherry-red spots** or such severe early neurological regression. - It is caused by a deficiency of **glucocerebrosidase**, leading to accumulation of glucocerebroside in **Gaucher cells** (not foamy histiocytes). - The infantile neuronopathic form (type 2) can present early but lacks cherry-red spots. *Incorrect: Wolman disease* - Wolman disease is a lysosomal storage disorder caused by **lysosomal acid lipase deficiency**, presenting with hepatosplenomegaly, failure to thrive, and foamy histiocytes. - Key distinguishing feature: **bilateral adrenal calcifications** on imaging, which are pathognomonic for Wolman disease but not mentioned in this case. - Does **not** typically cause cherry-red spots on fundoscopic examination. *Incorrect: GM1 gangliosidosis* - GM1 gangliosidosis can present with hepatosplenomegaly, developmental delay, and **cherry-red spots** (in about 50% of cases). - However, it is characterized by distinctive **coarse facial features**, **skeletal dysplasia** (dysostosis multiplex), and **vacuolated lymphocytes** on blood smear. - The **foamy histiocytes** and prominent pulmonary involvement are more characteristic of Niemann-Pick disease type A.

Question 4: A 26-year-old woman presents to a physician for genetic counseling, because she is worried about trying to have a child. Specifically, she had 2 siblings that died young from a lysosomal storage disorder and is afraid that her own children will have the same disorder. Her background is Ashkenazi Jewish, but she says that her husband's background is mixed European heritage. Her physician says that since her partner is not of Jewish background, their chance of having a child with Niemann-Pick disease is dramatically decreased. Which of the following genetic principles best explains why there is an increased prevalence of this disease in some populations?

A. Natural selection
B. Imprinting
C. De novo mutations
D. Gene flow
E. Founder effect (Correct Answer)

Explanation: ***Founder effect*** - The **founder effect** occurs when a new population is established by a small number of individuals, leading to a **reduced genetic diversity** and an increased frequency of certain alleles that were present in the founders. This is particularly relevant in populations like **Ashkenazi Jews**, who descended from a small, isolated group with certain allele frequencies. - In this scenario, the high prevalence of **Niemann-Pick disease** (and other genetic disorders) in the Ashkenazi Jewish population is due to their historical isolation and intermarriage within a relatively small gene pool, trapping and concentrating certain alleles. *Natural selection* - **Natural selection** typically describes the process by which traits that enhance survival and reproduction become more common in a population over time, or deleterious traits become less common. - While it can influence disease prevalence, it doesn't primarily explain the disproportionately high frequency of rare recessive disorders in specific isolated populations in the manner described. *Imprinting* - **Genomic imprinting** refers to the phenomenon where certain genes are expressed in a **parent-of-origin-specific manner**, meaning that only the allele inherited from either the mother or the father is expressed. - This mechanism explains certain genetic conditions but does not account for the increased prevalence of a recessive disorder due to population history and isolation. *De novo mutations* - **De novo mutations** are new genetic alterations that appear for the first time in an individual and are not inherited from either parent. - While de novo mutations are a source of genetic variation, they do not explain the high prevalence of a specific ancestral allele within an entire population. *Gene flow* - **Gene flow** (or migration) is the transfer of genetic material from one population to another, which tends to **decrease genetic differences** between populations and introduce new alleles. - This principle would suggest a *reduction* in the prevalence of specific rare alleles over time as populations mix, rather than an *increase* in isolated groups.

Question 5: A 3-month-old infant is brought to her pediatrician for a well-child visit. The infant was born to a 22-year-old mother via a spontaneous vaginal delivery at 38 weeks of gestation in her home. She moved to the United States approximately 3 weeks ago from a small village. She reports that her infant had 2 episodes of non-bloody and non-bilious vomiting. The infant's medical history includes eczema and 2 seizure episodes that resolved with benzodiazepines in the emergency department. Physical examination is notable for a musty body odor, eczema, and a fair skin complexion. Which of the following is the best next step in management?

A. Dietary restriction (Correct Answer)
B. Abdominal radiography
C. Dermatology consult
D. MRI of the brain
E. Antiepileptic drug

Explanation: ***Dietary restriction*** - The infant's symptoms, including **eczema**, **seizures**, **fair skin**, and a distinctive "musty" odor, strongly suggest **phenylketonuria (PKU)**. PKU is an **autosomal recessive metabolic disorder** where the body cannot properly break down **phenylalanine**. - The primary treatment for PKU is a **lifelong diet low in phenylalanine**. This involves restricting high-protein foods and using special medical formulas to provide adequate nutrition. Early and strict dietary management is crucial to prevent intellectual disability and other neurological complications. *Abdominal radiography* - While the infant experienced vomiting, the description of it being **non-bloody** and **non-bilious**, along with the absence of other gastrointestinal symptoms like distension, makes a significant abdominal pathology less likely than **metabolic derangement**. - Abdominal radiography would be more appropriate for suspected **bowel obstruction** or perforation, for which there are no strong indications in this case. *Dermatology consult* - The presence of eczema is noted, but it is one of several symptoms pointing towards a **systemic metabolic disorder** rather than an isolated skin condition. - Addressing the underlying metabolic cause (PKU) through dietary restriction will likely improve or resolve the eczema, making a consult for symptomatic treatment a secondary concern. *MRI of the brain* - The infant has experienced seizures, which often prompt neurological imaging. However, in the context of the other clinical findings (musty odor, fair skin, eczema), the seizures are highly suggestive of **metabolic encephalopathy** due to PKU. - While an MRI might show changes related to chronic phenylalanine toxicity, the most urgent and effective intervention is to address the metabolic cause through **dietary restriction**. *Antiepileptic drug* - Starting an antiepileptic drug might control the seizures symptomatically, but it would **not address the underlying cause** of the seizures, which is the metabolic disturbance in PKU. - **Untreated PKU** will lead to progressive neurological damage and intellectual disability even if seizures are controlled, highlighting the importance of root cause treatment.

Question 6: A research study evaluates three siblings with Niemann-Pick disease type C: a 6-year-old with ataxia and vertical supranuclear gaze palsy, a 10-year-old with hepatosplenomegaly and mild cognitive impairment, and a 14-year-old who is asymptomatic. Genetic testing reveals all three carry the same compound heterozygous NPC1 mutations. Fibroblast studies show similar cholesterol esterification defects and filipin staining patterns. Miglustat therapy is available. Evaluate the biological basis for phenotypic variability and optimal treatment allocation.

A. Evaluate modifier genes, epigenetic factors, and biomarkers; treat based on individual risk stratification (Correct Answer)
B. Treat all three immediately as genetic identity predicts identical disease course
C. Treat only symptomatic siblings as asymptomatic carrier won't develop disease
D. Delay all treatment until symptoms appear in the youngest to confirm diagnosis
E. Treat the 6-year-old only as neurologic symptoms indicate blood-brain barrier dysfunction

Explanation: ***Evaluate modifier genes, epigenetic factors, and biomarkers; treat based on individual risk stratification*** - **Phenotypic discordance** in Niemann-Pick type C (NPC) despite identical genotypes suggests that **modifier genes**, **epigenetic factors**, and cellular environment dictate clinical onset and severity. - Management must be personalized because **NPC1 mutations** and **filipin staining** do not perfectly correlate with clinical progression; biomarkers like **oxysterols** or **lysosphingolipids** help guide individual risk. *Treat only symptomatic siblings as asymptomatic carrier won't develop disease* - The asymptomatic 14-year-old is not a carrier but has already been confirmed to have **compound heterozygous NPC1 mutations** and pathognomonic **filipin staining**. - This sibling has the disease and is at high risk for **late-onset neurological symptoms**, requiring proactive monitoring rather than being dismissed as a carrier. *Treat all three immediately as genetic identity predicts identical disease course* - Even with identical **NPC1 mutations**, clinical presentation varies significantly (from **supranuclear gaze palsy** to asymptomatic), meaning the disease course is not identical. - While **Miglustat** is effective, immediate treatment in asymptomatic patients is debated; therapy is typically tailored to clinical or **biomarker evidence** of progression. *Treat the 6-year-old only as neurologic symptoms indicate blood-brain barrier dysfunction* - **Miglustat** crosses the **blood-brain barrier** to inhibit **glucosylceramide synthase**, but its use is not limited based on blood-brain barrier integrity. - The 10-year-old already exhibits **hepatosplenomegaly** and **cognitive impairment**, which are clear indications for therapy to prevent further neurocognitive decline. *Delay all treatment until symptoms appear in the youngest to confirm diagnosis* - The diagnosis is already confirmed via **genetic testing** showing NPC1 mutations and **fibroblast studies** showing cholesterol defects. - Delaying treatment in already symptomatic siblings (the 6 and 10-year-olds) would allow irreversible **neuronal loss** and worsening of **ataxia**.

Question 7: A 15-year-old boy with Hunter syndrome (MPS II) on weekly enzyme replacement therapy develops IgG antibodies with high neutralizing capacity against idursulfase. His symptoms have worsened over the past 6 months with increasing hepatosplenomegaly and joint stiffness. His brother with the same mutation shows excellent response to ERT without antibody formation. Synthesize an appropriate management plan considering immunologic and genetic factors.

A. Switch to substrate reduction therapy as primary treatment
B. Implement immune tolerance induction protocol with immunosuppression and continued ERT (Correct Answer)
C. Discontinue ERT as antibodies make it ineffective; switch to supportive care only
D. Perform HSCT to eliminate antibody production and provide endogenous enzyme
E. Increase ERT dose to saturate antibody binding capacity

Explanation: ***Implement immune tolerance induction protocol with immunosuppression and continued ERT*** - The presence of **high-titer neutralizing IgG antibodies** (NABs) interferes with the efficacy of **idursulfase**, leading to the recurrence of symptoms like **hepatosplenomegaly** and joint stiffness. - **Immune tolerance induction (ITI)** using agents like **rituximab**, **methotrexate**, and IVIG is indicated to eliminate the antibody response and restore the clinical benefit of the **enzyme replacement therapy**. *Discontinue ERT as antibodies make it ineffective; switch to supportive care only* - Stopping ERT allows the accumulation of **glycosaminoglycans** to continue, leading to progressive multisystemic decline and shortened **life expectancy**. - Supportive care alone does not address the underlying **biochemical deficiency** when immune modulation could potentially rescue the primary treatment. *Switch to substrate reduction therapy as primary treatment* - **Substrate reduction therapy** (SRT) is not currently the standard or approved primary treatment for **Hunter syndrome** (MPS II) especially in the context of existing ERT failure. - SRT aims to reduce the synthesis of **heparan and dermatan sulfate**, but it does not replace the missing **iduronate-2-sulfatase** enzyme activity required for clearance. *Increase ERT dose to saturate antibody binding capacity* - Increasing the dose of **idursulfase** often fails to overcome high-affinity **neutralizing antibodies** and may increase the risk of **infusion-related reactions** or immune complex formation. - Antibody **saturation** is not a sustainable or effective clinical strategy for managing high-titer **anti-drug antibodies** in lysosomal storage diseases. *Perform HSCT to eliminate antibody production and provide endogenous enzyme* - While **hematopoietic stem cell transplantation** (HSCT) provides endogenous enzyme, it is not the preferred treatment for **MPS II** due to high procedural risks and inconsistent neurological outcomes compared to MPS I. - HSCT is typically not used specifically as a secondary measure to treat **anti-drug antibodies** when **immune tolerance induction** is a viable and less invasive option.

Question 8: A newborn screening program identifies an infant with deficient β-glucuronidase activity. The infant is currently asymptomatic at 2 weeks of age. The parents are counseled about Sly syndrome (MPS VII) and ask about prognosis. Genetic testing reveals the infant is compound heterozygous with one null allele and one missense mutation (p.P408S) that retains 8% residual enzyme activity. Evaluate the most appropriate management strategy.

A. Begin enzyme replacement therapy immediately to prevent neurologic damage
B. Wait and observe, as 8% residual activity will prevent disease manifestation
C. Immediate hematopoietic stem cell transplantation before symptoms develop
D. Gene therapy followed by enzyme replacement as bridging therapy
E. Initiate early enzyme replacement therapy with neurodevelopmental monitoring, consider HSCT if CNS involvement develops (Correct Answer)

Explanation: ***Initiate early enzyme replacement therapy with neurodevelopmental monitoring, consider HSCT if CNS involvement develops*** - **Sly syndrome (MPS VII)** management focuses on early intervention with **ERT (vestronidase alfa)** to reduce systemic **glycosaminoglycan (GAG)** accumulation and mitigate skeletal/organ damage. - A **missense mutation** with **8% residual activity** often suggests an attenuated phenotype; early therapy combined with close monitoring allows for tailoring aggressive interventions like **HSCT** if CNS features emerge. *Immediate hematopoietic stem cell transplantation before symptoms develop* - **HSCT** is associated with significant **morbidity and mortality** and is typically reserved for severe, early-onset cases where the benefit for the CNS outweighs the procedural risks. - Given the infant's **8% residual activity**, an immediate transplant may be premature without first assessing the efficacy of less invasive **enzyme replacement therapy**. *Wait and observe, as 8% residual activity will prevent disease manifestation* - While 8% activity indicates an **attenuated form**, it is insufficient to prevent the progressive accumulation of GAGs that leads to **dysostosis multiplex** and organomegaly. - **Sly syndrome** is progressive; the

Question 9: A 5-year-old boy with known Gaucher disease type 1 has been on enzyme replacement therapy with imiglucerase for 2 years. His hepatosplenomegaly has decreased and bone pain has improved. However, his mother is concerned about the frequency of IV infusions. Laboratory testing shows he is homozygous for the N370S mutation. Analyze which alternative therapy would be most appropriate and why.

A. Perform hematopoietic stem cell transplantation
B. Switch to substrate reduction therapy with eliglustat (Correct Answer)
C. Continue imiglucerase as no alternatives exist for his genotype
D. Use chaperone therapy with ambroxol
E. Begin gene therapy with glucocerebrosidase vector

Explanation: ***Switch to substrate reduction therapy with eliglustat*** - **Eliglustat** is an oral **substrate reduction therapy (SRT)** that inhibits **glucosylceramide synthase**, making it a viable alternative for patients with the **N370S mutation** (Gaucher type 1) who find IV infusions burdensome. - In clinical trials for stable patients transitioning from ERT, it has demonstrated maintenance of therapeutic goals including **spleen volume**, **liver volume**, and **hemoglobin levels**. *Continue imiglucerase as no alternatives exist for his genotype* - This is incorrect because **substrate reduction therapies** (SRT) like **eliglustat** and **miglustat** are approved alternatives for patients with **non-neuronopathic (Type 1)** Gaucher disease. - While **imiglucerase (ERT)** is effective, patient preference and **quality of life** concerns regarding infusion frequency are valid reasons to explore approved oral alternatives. *Perform hematopoietic stem cell transplantation* - **HSCT** is generally reserved for severe cases or **Type 3** Gaucher disease where ERT cannot cross the **blood-brain barrier**; it is not indicated for a patient already responding well to ERT. - The procedure carries significant risks of **morbidity and mortality**, making it an inappropriate choice for a well-managed case of **Type 1** disease. *Begin gene therapy with glucocerebrosidase vector* - While **gene therapy** is an area of intense research for lysosomal storage disorders, it is not currently a **standard of care** or widely available clinical alternative for Gaucher disease. - The child's symptoms are currently managed, so experimental or **investigational treatments** are not clinically indicated over established oral therapies. *Use chaperone therapy with ambroxol* - **Ambroxol** acts as a **pharmacological chaperone** that can increase the activity of certain misfolded glucocerebrosidase variants, but its use in Gaucher disease remains **off-label**. - It has primarily been studied as an adjunctive therapy for **neuronopathic forms** (Type 2 and 3) and is not the first-line alternative to ERT for a child with stable Type 1 disease.

Question 10: A 28-year-old man presents with episodes of severe burning pain in his hands and feet, angiokeratomas on his trunk, and decreased sweating. He reports similar symptoms in his maternal uncle who died of renal failure at age 42. Echocardiography shows left ventricular hypertrophy. Serum creatinine is 1.8 mg/dL with proteinuria. Analysis of his lysosomal enzyme profile shows deficiency in one enzyme. What mechanism explains his cardiac manifestations?

A. Secondary amyloidosis from chronic inflammation
B. Direct cardiotoxic effect of accumulated ceramide trihexoside
C. Glycosphingolipid accumulation causing myocyte hypertrophy and fibrosis (Correct Answer)
D. Valvular insufficiency from mucopolysaccharide deposition
E. Coronary artery disease from endothelial dysfunction

Explanation: ***Glycosphingolipid accumulation causing myocyte hypertrophy and fibrosis*** - This patient presents with **Fabry disease**, an X-linked recessive lysosomal storage disorder caused by a deficiency of **alpha-galactosidase A**. - The deficiency leads to the progressive accumulation of **globotriaosylceramide (Gb3)** in cardiomyocytes, causing **left ventricular hypertrophy**, conduction abnormalities, and eventual cardiac fibrosis. *Direct cardiotoxic effect of accumulated ceramide trihexoside* - While **ceramide trihexoside** (Gb3) accumulates in Fabry disease, the cardiac pathology is due to mechanical **pressure/infiltration** and metabolic stress rather than a direct biochemical toxin effect. - The damage is primarily structural, involving **lysosomal engorgement** within the cells rather than acute toxicity. *Secondary amyloidosis from chronic inflammation* - **Secondary (AA) amyloidosis** results from chronic inflammatory states like rheumatoid arthritis or bronchiectasis, which are not present here. - Fabry disease can mimic amyloidosis on imaging due to **wall thickening**, but the underlying substance is **globotriaosylceramide**, not amyloid fibrils. *Coronary artery disease from endothelial dysfunction* - Although Gb3 accumulates in the **vascular endothelium** and can cause myocardial ischemia, the primary cause of the noted **left ventricular hypertrophy** is infiltrative myocyte disease. - Classic coronary artery disease (atherosclerosis) is not the typical primary mechanism for the **multi-organ failure** and hypertrophy seen in young Fabry patients. *Valvular insufficiency from mucopolysaccharide deposition* - **Mucopolysaccharide deposition** is characteristic of **Mucopolysaccharidoses** (e.g., Hurler or Hunter syndrome), not Fabry disease. - While Fabry patients can have minor valvular thickening, the clinical picture of **angiokeratomas**, **acroparesthesia**, and renal failure points specifically to a **sphingolipidosis**.

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