Lysosomal storage disease is a collective term for the various metabolic disorders due to defects in lysosomal function resulting in an abnormal accumulation of toxic materials in the cell. Cystinosis is one of the types of lysosomal storage disease.
Cystinosis is characterized by the buildup of cystine crystals in the lysosomes of cells, particularly reticuloendothelial cells. The buildup is caused by a defective enzyme transporting cystine. The deficiency is associated with a defect in the CTNS gene on chromosome 17p. The gene codes for cystinosin (a lysosomal membrane-specific transporter). In particular, cystinosin transports cystine from the lysosomes into the cytosol. Thus, failure of this protein to transport cystine, the outcome is the accumulation of cystine in the lysosomes. Cystine in large amounts tends to form crystalline precipitates in organs and tissues (such as bone marrow, cornea, etc.).
The condition is inherited in an autosomal recessive pattern. This means that the individual has two copies of the defective gene and therefore manifests symptoms associated with the disease. A carrier of the disease would have only one copy of the defective gene and therefore may not show symptoms.
- cystine storage disease