Cystinosis
| Cystinosis | |
|---|---|
 |
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| Chemical structure of cystine formed from L-cysteine (under biological conditions) | |
| Classification and external resources | |
| Specialty | endocrinology |
| ICD-10 | E72.0 |
| ICD-9-CM | 270.0 |
| DiseasesDB | 3382 |
| eMedicine | ped/538 |
| MeSH | D003554 |
Cystinosis is a lysosomal storage disease characterized by the abnormal accumulation of the amino acid cystine. It is a genetic disorder that typically follows an autosomal recessive inheritance pattern. Cystinosis is the most common cause of Fanconi syndrome in the pediatric age group. Fanconi syndrome occurs when the function of cells in renal tubules are impaired, leading to abnormal amounts of carbohydrates and amino acids in the urine, excessive urination, and low blood levels of potassium and phosphates.
Cystinosis was the first documented genetic disease belonging to the group of Lysosomal storage disease disorders. It is a rare autosomal recessive disorder resulting from accumulation of free cystine in lysosomes, eventually leading to intracellular crystal formation throughout the body. Cystinosis is caused by mutations in the CTNS gene that codes for cystinosin, the lysosomal membrane-specific transporter for cystine. Intracellular metabolism of cystine, as it happens with all amino acids, requires its transport across the cell membrane. After degradation of endocytosed protein to cystine within lysosomes, it is normally transported to the cytosol. But if there is a defect in the carrier protein, cystine is accumulated in lysosomes. As cystine is highly insoluble, when its concentration in tissue lysosomes increase, its solubility is immediately exceeded and crystalline precipitates are formed in almost all organs and tissues.
However, the progression of the disease is not related to the presence of crystals in target tissues. Although tissue damage might depend on cystine accumulation, the mechanisms of tissue damage are not fully understood. Increased intracellular cystine profoundly disturbs cellular oxidative metabolism and glutathione status, leading to altered energy metabolism, autophagy, and apoptosis.
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