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.
Q2
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.
Q3
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.
Q4
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.
Q5
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?
Q6
A 7-year-old boy presents with progressive gait disturbance and declining school performance over 6 months. MRI shows bilateral periventricular white matter abnormalities with frontal predominance. Nerve conduction studies reveal decreased conduction velocity. Urine analysis shows elevated sulfatides and arylsulfatase A activity is markedly decreased. His 5-year-old sister is asymptomatic but has arylsulfatase A activity at 55% of normal. Analyze the genetic counseling implications for the sister.
Q7
A 3-year-old girl presents with hypotonia and cardiomegaly. She has a history of poor feeding since infancy. Physical examination reveals macroglossia and hepatomegaly. ECG shows shortened PR interval and tall QRS complexes. Muscle biopsy reveals periodic acid-Schiff (PAS) positive material that is sensitive to diastase digestion. What treatment approach should be initiated?
Q8
A 4-year-old boy presents with aggressive behavior, intellectual disability, and self-mutilating behavior including biting his fingers and lips. Laboratory findings show elevated uric acid levels and orange crystals in his diaper. His parents report the symptoms began around 6 months of age. Which enzyme deficiency best explains this clinical presentation?
Q9
A 6-month-old Ashkenazi Jewish infant presents with progressive weakness, loss of head control, and an exaggerated startle response to noise. Fundoscopic examination reveals a cherry-red spot on the macula. The infant has normal liver and spleen size. Laboratory studies show normal urinary mucopolysaccharides. What is the accumulated substrate in this patient's neurons?
Q10
A 9-month-old boy is brought to the clinic with progressive developmental regression and loss of previously acquired motor skills. Physical examination reveals coarse facial features, hepatosplenomegaly, and a gibbus deformity of the lumbar spine. Ophthalmologic examination shows corneal clouding. Urinalysis demonstrates increased dermatan and heparan sulfate. What enzyme deficiency is most likely responsible for this patient's condition?
Lysosomal storage diseases US Medical PG Practice Questions and MCQs
Question 1: 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 2: 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 3: 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 4: 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 5: 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**.
Question 6: A 7-year-old boy presents with progressive gait disturbance and declining school performance over 6 months. MRI shows bilateral periventricular white matter abnormalities with frontal predominance. Nerve conduction studies reveal decreased conduction velocity. Urine analysis shows elevated sulfatides and arylsulfatase A activity is markedly decreased. His 5-year-old sister is asymptomatic but has arylsulfatase A activity at 55% of normal. Analyze the genetic counseling implications for the sister.
A. She may have pseudodeficiency and requires additional testing (Correct Answer)
B. She is a carrier and will remain asymptomatic
C. She will definitely develop the disease by age 10
D. She has the adult-onset form and will develop symptoms in her 30s
E. She requires immediate enzyme replacement therapy
Explanation: ***She may have pseudodeficiency and requires additional testing***
- In the context of **Metachromatic Leukodystrophy (MLD)**, individuals may possess **pseudodeficiency alleles** that lead to low in vitro **arylsulfatase A** activity (often 5-20% of normal) without causing clinical disease or sulfatide accumulation.
- Since her activity (55%) is significantly lower than average but she is asymptomatic, further testing like **urinary sulfatide excretion** or **genetic sequencing** is needed to distinguish between a **carrier, a pseudodeficient individual, or a normal variant**.
*She will definitely develop the disease by age 10*
- The disease is **autosomal recessive**, and an enzyme activity of 55% is well above the threshold (typically <10%) required to prevent the accumulation of **galactosyl sulfatide** in the central and peripheral nervous system.
- Clinical symptoms like **gait disturbance** and **periventricular white matter abnormalities** only occur when enzyme activity is severely deficient.
*She is a carrier and will remain asymptomatic*
- While 55% activity is consistent with being a **heterozygous carrier**, enzyme levels alone are not definitive due to the high prevalence of **ASA pseudodeficiency alleles** in the general population.
- Carriers remain asymptomatic, but without confirming the specific mutations, one cannot rule out that her levels are simply on the lower end of the **normal distribution range**.
*She requires immediate enzyme replacement therapy*
- **Enzyme replacement therapy** or hematopoietic stem cell transplantation is indicated only for symptomatic patients or those with confirmed clinical-grade **biochemical deficiency**.
- Treating an asymptomatic individual with **55% enzyme activity** would be inappropriate, as she does not manifest the **leukodystrophy** pathology.
*She has the adult-onset form and will develop symptoms in her 30s*
- Adult-onset MLD typically presents with **psychiatric symptoms** or cognitive decline and is still associated with significantly lower enzyme levels than 55%.
- The proband's **juvenile onset** (7 years old) suggests specific mutations; the sister's high enzyme level makes any form of clinical MLD highly unlikely.
Question 7: A 3-year-old girl presents with hypotonia and cardiomegaly. She has a history of poor feeding since infancy. Physical examination reveals macroglossia and hepatomegaly. ECG shows shortened PR interval and tall QRS complexes. Muscle biopsy reveals periodic acid-Schiff (PAS) positive material that is sensitive to diastase digestion. What treatment approach should be initiated?
A. Bone marrow transplantation
B. Enzyme replacement therapy with acid α-glucosidase (Correct Answer)
C. High-protein diet with frequent meals
D. Substrate reduction therapy with miglustat
E. Dietary restriction of phenylalanine
Explanation: ***Enzyme replacement therapy with acid ̑-glucosidase***
- The clinical presentation of **hypotonia**, **cardiomegaly**, and **macroglossia** combined with high-voltage QRS and shortened PR interval on ECG points directly to **Pompe disease** (GSD Type II).
- This treatment addresses the underlying **acid ̑-1,4-glucosidase** deficiency by clearing **lysosomal glycogen** accumulation, which is evidenced by the **PAS-positive** diastase-sensitive material in muscle biopsy.
*High-protein diet with frequent meals*
- This approach is typically used to manage **Cori disease** (GSD Type III) to maintain euglycemia and provide amino acids for gluconeogenesis.
- It does not prevent the **cardiac failure** or life-threatening systemic glycogen storage associated with lysosomal enzyme defects.
*Bone marrow transplantation*
- While used for some lysosomal storage diseases like **Hurler syndrome**, it is not the standard of care for Pompe disease due to limited efficacy in skeletal and cardiac muscle recovery.
- **Enzyme replacement therapy** is the preferred and more targeted clinical intervention for this specific condition.
*Dietary restriction of phenylalanine*
- This is the primary treatment for **Phenylketonuria (PKU)** to prevent intellectual disability and neurological sequelae.
- It has no relevance to **glycogen metabolism** or the hypertrophic cardiomyopathy seen in this patient.
*Substrate reduction therapy with miglustat*
- This therapy is used in **Gaucher disease** Type 1 to decrease the production of glucosylceramide.
- It is not indicated for Pompe disease, where the problem is the inability to degrade **glycogen** within the lysosomes rather than sphingolipid accumulation.
Question 8: A 4-year-old boy presents with aggressive behavior, intellectual disability, and self-mutilating behavior including biting his fingers and lips. Laboratory findings show elevated uric acid levels and orange crystals in his diaper. His parents report the symptoms began around 6 months of age. Which enzyme deficiency best explains this clinical presentation?
A. Hypoxanthine-guanine phosphoribosyltransferase (Correct Answer)
B. α-galactosidase A
C. Acid maltase
D. Arylsulfatase A
E. Glucose-6-phosphatase
Explanation: ***Hypoxanthine-guanine phosphoribosyltransferase***
- This patient presents with the classic triad of **Lesch-Nyhan syndrome**, an X-linked recessive disorder characterized by **hyperuricemia**, **intellectual disability**, and compulsive **self-mutilation**.
- The deficiency of **HGPRT** disrupts the **purine salvage pathway**, leading to an over-accumulation of PRPP and subsequent overproduction of **uric acid**, often seen as **orange crystals** (sodium urate) in the diaper.
*Glucose-6-phosphatase*
- Deficiency causes **Von Gierke disease** (GSD Type I), which presents with severe **fasting hypoglycemia**, **hepatomegaly**, and lactic acidosis.
- While **hyperuricemia** can occur due to competition for renal excretion, it does not present with the specific **behavioral/neurological symptoms** like self-biting.
*Arylsulfatase A*
- Deficiency leads to **Metachromatic leukodystrophy**, a lysosomal storage disease resulting in the accumulation of **sulfatides** in the central and peripheral nervous system.
- It causes **demyelination** leading to ataxia and dementia, but it is not associated with **hyperuricemia** or self-mutilating behavior.
*α-galactosidase A*
- Deficiency causes **Fabry disease**, characterized by an accumulation of **ceramide trihexoside**.
- Clinical features include **angiokeratomas**, peripheral neuropathy, and renal failure, but not **hyperuricemia** or intellectual disability.
*Acid maltase*
- Also known as **alpha-1,4-glucosidase**, its deficiency causes **Pompe disease** (GSD Type II).
- It is characterized by **cardiomyopathy**, hypotonia, and respiratory failure, lacking the **purine metabolism** abnormalities seen in this case.
Question 9: A 6-month-old Ashkenazi Jewish infant presents with progressive weakness, loss of head control, and an exaggerated startle response to noise. Fundoscopic examination reveals a cherry-red spot on the macula. The infant has normal liver and spleen size. Laboratory studies show normal urinary mucopolysaccharides. What is the accumulated substrate in this patient's neurons?
A. GM2 ganglioside (Correct Answer)
B. Galactocerebroside
C. Sulfatide
D. Sphingomyelin
E. Glucocerebroside
Explanation: ***GM2 ganglioside***
- The patient presents with symptoms of **Tay-Sachs disease**, a lysosomal storage disorder caused by a deficiency in **Hexosaminidase A**, leading to the accumulation of **GM2 ganglioside** in lysosomes.
- Clinical features include **progressive neurodegeneration**, an **exaggerated startle response** (hyperacusis), and a **cherry-red spot** on the macula without hepatosplenomegaly.
*Glucocerebroside*
- **Glucocerebroside** accumulates in **Gaucher disease** due to a deficiency of **glucocerebrosidase**.
- It characteristically presents with **hepatosplenomegaly** and bone marrow involvement (Gaucher cells), which are absent in this infant.
*Sphingomyelin*
- Accumulation of **sphingomyelin** occurs in **Niemann-Pick disease** due to a deficiency in **sphingomyelinase**.
- While it also features a **cherry-red spot**, it is distinguished from Tay-Sachs by the hallmark presence of **hepatosplenomegaly**.
*Galactocerebroside*
- **Galactocerebroside** accumulates in **Krabbe disease** due to a deficiency of **galactocerebrosidase**.
- This condition results in **demyelination** and presents with irritability and **globoid cells**, but does not present with a cherry-red spot.
*Sulfatide*
- **Sulfatides** accumulate in **Metachromatic Leukodystrophy** due to a deficiency of **Arylsulfatase A**.
- This disorder presents with central and peripheral **demyelination** leading to ataxia and dementia, rather than the rapid motor regression and cherry-red spot seen here.
Question 10: A 9-month-old boy is brought to the clinic with progressive developmental regression and loss of previously acquired motor skills. Physical examination reveals coarse facial features, hepatosplenomegaly, and a gibbus deformity of the lumbar spine. Ophthalmologic examination shows corneal clouding. Urinalysis demonstrates increased dermatan and heparan sulfate. What enzyme deficiency is most likely responsible for this patient's condition?
A. α-L-iduronidase (Correct Answer)
B. Sphingomyelinase
C. Hexosaminidase A
D. Galactocerebrosidase
E. Iduronate-2-sulfatase
Explanation: ***̑-L-iduronidase***
- The patient presents with **Hurler syndrome (MPS I)**, which is caused by a deficiency in **̑-L-iduronidase**, leading to the accumulation of **dermatan sulfate** and **heparan sulfate**.
- Clinical features such as **corneal clouding**, **coarse facial features**, **hepatosplenomegaly**, and **gibbus deformity** are classic diagnostic markers for this condition.
*Iduronate-2-sulfatase*
- This enzyme is deficient in **Hunter syndrome (MPS II)**, which shares findings like coarse facies and hepatosplenomegaly but lacks **corneal clouding**.
- It follows an **X-linked recessive** inheritance pattern, whereas Hurler syndrome is inherited in an **autosomal recessive** manner.
*Galactocerebrosidase*
- Deficiency causes **Krabbe disease**, a leukodystrophy characterized by the destruction of **myelin** and the presence of **globoid cells**.
- Clinical presentation includes **irritability**, **seizures**, and **optic atrophy**, rather than organomegaly or mucopolysacchariduria.
*Sphingomyelinase*
- A deficiency in this enzyme results in **Niemann-Pick disease (Type A/B)**, leading to the accumulation of **sphingomyelin**.
- While it features **hepatosplenomegaly** and **developmental regression**, it is distinguished by a **cherry-red spot** on the macula and an absence of **corneal clouding** or skeletal changes.
*Hexosaminidase A*
- Deficiency leads to **Tay-Sachs disease**, which presents with **progressive neurodegeneration** and a **cherry-red spot** on the macula.
- It is differentiated from Hurler syndrome by the **absence of hepatosplenomegaly** and the absence of **skeletal/facial coarse features**.
