What is the pathophysiology of cystinosis in Fanconi syndrome?

Updated: Feb 09, 2018
  • Author: Sahar Fathallah-Shaykh, MD; Chief Editor: Craig B Langman, MD  more...
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Answer

Cystinosis is one of the most common causes of Fanconi syndrome in children. The disease is caused by the accumulation of cystine in renal tubule cells. An experimental model of Fanconi syndrome was created by injecting rats with cystine dimethylester. Renal tubules exposed to this compound had a high concentration of cystine; low rates of transport; and decreased levels of ATP, oxygen consumption, and mitochondrial respiration. Addition of ATP to the incubation media partially corrected these abnormalities. Some postulate that the decrease in oxidative energy metabolism seen in many forms of Fanconi syndrome is caused by low intracellular phosphate, which results in a depletion of ATP precursors and an increase in adenine nucleotide degradation. Others have found elevated oxidized glutathione in the cystinotic proximal tubular epithelial cell line, suggesting increased oxidative stress that may contribute to tubular dysfunction in cystinosis.

Evidence supporting a role for alterations in tubule membrane permeability in the pathogenesis of Fanconi syndrome is limited. The luminal membrane permeability may increase in the maleic acid model and in animals injected with succinylacetone, the presumed toxin in tyrosinemia and another cause of Fanconi syndrome in humans.


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