Cystine disease

=Cystine Disease = Cystine disease, also known as cystinosis, is a rare genetic disorder characterized by the accumulation of the amino acid cystine within cells. This accumulation leads to the formation of crystals that can cause damage to various organs and tissues. Cystinosis is an autosomal recessive disorder, meaning that an individual must inherit two copies of the defective gene, one from each parent, to be affected.

Pathophysiology

Cystinosis is caused by mutations in the CTNS gene, which encodes the cystinosin protein. Cystinosin is responsible for transporting cystine out of lysosomes, cellular organelles that break down waste materials. When cystinosin is defective, cystine accumulates within lysosomes, forming crystals that can damage cells and tissues.

Clinical Manifestations

The symptoms of cystinosis vary depending on the age of onset and the organs affected. There are three main forms of cystinosis:

• Nephropathic Cystinosis: This is the most severe form, typically presenting in infancy. Symptoms include renal tubular Fanconi syndrome, growth retardation, and renal failure.
• Intermediate Cystinosis: Symptoms appear in late childhood or adolescence, with slower progression of renal disease.
• Non-nephropathic (Ocular) Cystinosis: This form primarily affects the eyes, causing photophobia and crystal deposits in the cornea.

Diagnosis

Diagnosis of cystinosis is based on clinical symptoms, family history, and laboratory tests. Measurement of cystine levels in leukocytes is a key diagnostic test. Genetic testing can confirm mutations in the CTNS gene.

Treatment

The primary treatment for cystinosis is cysteamine, a medication that reduces cystine levels in cells. Cysteamine is available in oral and ophthalmic formulations. Supportive treatments include management of renal complications and electrolyte imbalances.

Prognosis

With early diagnosis and treatment, individuals with cystinosis can have improved outcomes. However, the disease can lead to complications such as kidney failure, hypothyroidism, and muscle wasting.

Research and Future Directions

Research is ongoing to better understand the pathophysiology of cystinosis and to develop new treatments. Gene therapy and stem cell therapy are potential future approaches.

See Also

• Lysosomal storage disease
• Renal tubular Fanconi syndrome
• Autosomal recessive disorder
• Gahl, W. A., Thoene, J. G., & Schneider, J. A. (2002). Cystinosis: A disorder of lysosomal membrane transport. In The Metabolic and Molecular Bases of Inherited Disease (8th ed.).
• Nesterova, G., & Gahl, W. A. (2013). Cystinosis: The evolution of a treatable disease. Pediatric Nephrology, 28(1), 51-59.

NIH genetic and rare disease info

• NIH info on Cystine disease

Cystine disease is a rare disease.