Cystinosis

Cystinosis is an inherited lysosomal storage disorder in which cystine accumulates inside cells. It can damage the kidneys, eyes, and other organs, with severity varying by form and age of onset.

CTNS: CTNS is the gene encoding cystinosin, a transporter that moves cystine out of lysosomes. Most cystinosis-causing variants impair this lysosomal transport pathway.
Cysteamine: Cysteamine is a small molecule used to lower lysosomal cystine in cystinosis. It enters lysosomes and converts cystine into products that can leave without cystinosin.
Cystinuria: Cystinuria is an inherited kidney transport disorder that causes excess cystine in urine and recurrent stones. Unlike cystinosis, it does not cause lysosomal cystine accumulation throughout the body.
Autosomal recessive inheritance: Autosomal recessive inheritance occurs when disease results from pathogenic variants in both copies of an autosomal gene. Cystinosis usually develops when a person inherits a disease-causing CTNS variant from each parent.
Cystinosin: Cystinosin is a lysosomal membrane protein that exports cystine into the cytosol. Its loss traps cystine inside lysosomes in cystinosis.
Cystinosis diagnosis: Cystinosis diagnosis combines clinical findings with biochemical and genetic testing. Leukocyte cystine measurement and CTNS testing help confirm the disorder.
Nephropathic cystinosis: Nephropathic cystinosis is the severe form that begins in infancy and often causes early kidney disease. It is the form most associated with Fanconi syndrome and childhood kidney failure.
CTNS deletion: A CTNS deletion is a loss of DNA sequence within the gene encoding cystinosin. A common large deletion in CTNS accounts for many cases in some populations.
Cystine: Cystine is a disulfide-linked amino acid formed from two cysteine molecules. This poorly soluble molecule accumulates in cells when lysosomal export fails.
Leukocyte cystine measurement: Leukocyte cystine measurement quantifies cystine in white blood cells. It is used to assess cystine burden and monitor response to cysteamine.

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Oculocerebrorenal syndromeCompared with: It can cause proximal tubular dysfunction and eye findings, but results from cystine accumulation rather than OCRL deficiency.