Pathophysiology of Cystinosis

The amino acid cystine is a byproduct of protein degradation.1 Normally, cystine exits the lysosomal membrane through the transport protein cystinosin where it is reduced to 2 cysteine residues in the cytoplasm.2

Healthy Lysosome1

Illustration of healthy lysosome with functioning cystinosinIllustration of healthy lysosome with functioning cystinosin

Lysosome of Patient With Cystinosis1

Illustration of cystinosis pathophysiology as depicted by absent or defective cystinosin within a lysosomeIllustration of cystinosis pathophysiology as depicted by absent or defective cystinosin within a lysosome

The transport process is impaired in patients with cystinosis due to defective or absent cystinosin.1 As a result, continuous toxic intralysosomal accumulation and crystallization of cystine in cells throughout the body occur.1,3

Cystinosin is expressed throughout the body, leading to multisystemic dysfunction, and especially threatening the kidneys.4,5

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1. Gahl WA, Thoene JG, Schneider JA. Cystinosis. N Engl J Med. 2002;347(2):111-121. 2. Wilmer MJ, Schoeber JP, van den Heuvel LP, Levtchenko EN. Cystinosis: practical tools for diagnosis and treatment. Pediatr Nephrol. 2011;26(2):205-215. 3. Gahl WA, Balog JZ, Kleta R. Nephropathic cystinosis in adults: natural history and effects of oral cysteamine therapy. Ann Intern Med. 2007;147(4):242-250. 4. Jamalpoor A, Othman A, Levtchenko EN, Masereeuw R, Janssen MJ. Molecular mechanisms and treatment options of nephropathic cystinosis. Trends Mol Med. 2021;27(7):673-686. 5. Nesterova G, Gahl WA. Cystinosis: the evolution of a treatable disease. Pediatr Nephrol. 2013;28(1):51-59.