## **Core Concept**
Faber's disease, also known as **Hurler syndrome**, is a genetic disorder caused by the deficiency of an enzyme involved in the breakdown of glycosaminoglycans (GAGs). This condition is characterized by the accumulation of GAGs in various tissues, leading to multiple organ system involvement. The disorder is inherited in an autosomal recessive pattern.

## **Why the Correct Answer is Right**
The correct answer involves the deficiency of **alpha-L-iduronidase**. This enzyme is crucial for the degradation of dermatan sulfate and heparan sulfate, two types of glycosaminoglycans. In Hurler syndrome, the deficiency of alpha-L-iduronidase leads to the accumulation of these GAGs in the body, resulting in cellular dysfunction and the clinical manifestations of the disease, such as mental retardation, hoarseness, frequent infections (which could be misconstrued as dermatitis), and skeletal deformities.

## **Why Each Wrong Option is Incorrect**
- **Option A:** Deficiency of **sphingomyelinase** leads to Niemann-Pick disease, characterized by accumulation of sphingomyelin in cells, primarily affecting the liver, spleen, and lungs, and not matching the clinical presentation described.
- **Option B:** Deficiency of **glucocerebrosidase** causes Gaucher's disease, which involves the accumulation of glucocerebroside in macrophages, leading to hepatosplenomegaly, bone pain, and other systemic symptoms not specifically aligning with Faber's disease.
- **Option D:** Deficiency of **arylsulfatase B** results in Maroteaux-Lamy syndrome, another type of mucopolysaccharidosis (MPS) that presents with similar but not identical clinical features compared to Hurler syndrome.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that patients with Hurler syndrome (Faber's disease) often present with **cloudy corneas**, which is a distinctive feature helping in the differential diagnosis of mucopolysaccharidoses. Early diagnosis and intervention, including enzyme replacement therapy (ERT) and hematopoietic stem cell transplantation (HSCT), can significantly improve outcomes.

## **Correct Answer:** . alpha-L-iduronidase