Cystinosis is a lysosomal storage disease characterized by the abnormal accumulation of cystine, the oxidized dimer of the amino acid cysteine.

It is a rare autosomal recessive disorder resulting from accumulation of free cystine in lysosomes, eventually leading to intracellular crystal formation throughout the body.

[4] Cystinosis is caused by mutations in the CTNS gene that codes for cystinosin, the lysosomal membrane-specific transporter for cystine.

Infants affected by nephropathic cystinosis initially exhibit poor growth and particular kidney problems (sometimes called renal Fanconi syndrome).

The nutrient imbalances in the body lead to increased urination, thirst, dehydration, and abnormally acidic blood (acidosis).

Other signs and symptoms that may occur in patients include muscle deterioration, blindness, inability to swallow, impaired sweating, decreased hair and skin pigmentation, diabetes, and thyroid and nervous system problems.

If intermediate cystinosis is left untreated, complete kidney failure will occur, but usually not until the late teens to mid twenties.

[9] Cystinosis occurs due to a mutation in the gene CTNS, located on chromosome 17, which codes for cystinosin, the lysosomal cystine transporter.

This results in renal Fanconi syndrome,[12] and similar loss in other tissues can account for the short stature, retinopathy, and other features of the disease.

Definitive diagnosis and treatment monitoring are most often performed through measurement of white blood cell cystine level using tandem mass spectrometry.

If the kidneys become significantly impaired or fail, then treatment must be begun to ensure continued survival, up to and including renal transplantation.