The protein defective in cystinosis is responsible for
**Core Concept**
Cystinosis is a rare, autosomal recessive disorder characterized by the accumulation of cystine within lysosomes due to a defect in a specific protein. This accumulation leads to cellular dysfunction and ultimately results in various organ systems being affected.
**Why the Correct Answer is Right**
The protein defective in cystinosis is cystinosin, a lysosomal cystine transporter encoded by the CTNS gene. This protein is responsible for transporting cystine out of lysosomes, maintaining normal cystine levels within the cell. The mutation of the CTNS gene leads to a deficiency of cystinosin, causing cystine to accumulate within lysosomes. This accumulation triggers cellular damage and leads to the clinical manifestations of cystinosis.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as it does not specify a protein related to cystinosis. While it may be tempting to choose a protein involved in lysosomal function, it is not the specific protein defective in cystinosis.
**Option B:** This option is incorrect as it refers to a different disorder, Fabry disease. The protein defective in Fabry disease is alpha-Galactosidase A, not cystinosin.
**Option C:** This option is incorrect as it refers to a protein involved in a different lysosomal storage disorder, Hurler syndrome. The protein defective in Hurler syndrome is alpha-L-Iduronidase, not cystinosin.
**Option D:** This option is incorrect as it is a generic term and does not specify a protein related to cystinosis.
**Clinical Pearl / High-Yield Fact**
The CTNS gene is located on chromosome 17p13, and mutations in this gene are responsible for cystinosis. Understanding the genetic basis of cystinosis is crucial for diagnosis and management.
**Correct Answer: C. cystinosin**