Cystinosis: practical tools for diagnosis and treatment

Cystinosis is the major cause of inherited Fanconi syndrome, and should be suspected in young children with failure to thrive and signs of renal proximal tubular damage. The diagnosis can be missed in infants, because not all signs of renal Fanconi syndrome are present during the first months of life. In older patients cystinosis can mimic idiopathic nephrotic syndrome due to focal and segmental glomerulosclerosis. Measuring elevated white blood cell cystine content is the corner stone for the diagnosis. The diagnosis is confirmed by molecular analysis of the cystinosin gene. Corneal cystine crystals are invariably present in all patients with cystinosis after the age of 1 year. Treatment with the cystine depleting drug cysteamine should be initiated as soon as possible and continued lifelong to prolong renal function survival and protect extra-renal organs. This educational feature provides practical tools for the diagnosis and treatment of cystinosis

Reply to the letter from J.H.H. Ehrich.

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Conditionally Immortalized Human Proximal-Tubular Epithelial Cells Isolated from the Urine of a Healthy Subject Express Functional Calcium- Sensing Receptor (CaSR)

Background: The calcium-sensing receptor (CaSR) is a G protein coupled receptor, which plays an essential role in regulating Ca2+ homeostasis. Here we show that conditionally immortalized proximal tubular epithelial cell line (ciPTEC) obtained by immortalizing and subcloning cells exfoliated in the urine of a healthy subject expresses functional endogenous CaSR. Methods: Primary cells isolated from human urine sediment were infected with SV40T and hTERT vectors. Subconfluent cell layers were transferred to 33°C and selected by antibiotics for 15 days. Cells were subcloned and expanded to 70% confluence at 33°C. After maturation at 37°C for 10 days, the cloned cells were used. Results: The obtained ciPTEC cells expressed ZO-1 protein and aquaporin 1 thus confirming their epithelial and PT origin respectively. The expression of the endogenous CaSR in ciPTEC was confirmed by Western blotting revealing the immunodetection of both forms at 130 and ~200 kDa, corresponding to the monomeric and mature receptor. Of note, functional studies with Fura2-AM indicated that the physiological agonist, calcium (Ca2+), and the calcimimetic NPS-R568, induced a significant increase in cytosolic calcium, proving a high sensitivity of the endogenous receptor to low concentrations of its agonists. Cytosolic calcium levels were 46.2±2.22% (vs ATP 100%) after stimulation with 2.5μM Ca2+ and to the 37±1.76% (vs ATP 100%) after stimulation with 2.5μM NPS-R568. Calcium depletion from the ER using CPA (cyclopiazonic acid) abolished the increase in cytosolic calcium elicited by NPS-R568 confirming the origin of calcium exit from intracellular stores. Conclusions: We conclude that human proximal tubular ciPTEC cells express functional CaSR and respond to its activation with a release of calcium from the ER. These cell lines represent a valuable tool for research into the disorder associated with gain or loss of function of the CaSR by producing cell lines from patients. 

Mitochondrial complex V expression and activity in cystinotic fibroblasts.

Contains fulltext : 69400.pdf (publisher's version ) (Closed access)Alterations in ATP metabolism have been proposed to be involved in the pathogenesis of cystinosis, the most common form of inherited Fanconi syndrome. A recent study showed normal activity of respiratory chain complexes I-IV with decreased ATP levels in cystinotic fibroblasts. Here, we show normal complex V expression and activity in mitochondria of cystinotic fibroblasts. This indicates that alterations in mitochondrial oxidative phosphorylation enzymes are not responsible for ATP decrease in cystinotic fibroblasts

The pathogenesis of cystinosis: mechanisms beyond cystine accumulation.

Contains fulltext : 87778.pdf (publisher's version ) (Closed access)Renal proximal tubules are highly sensitive to ischemic and toxic insults and are affected in diverse genetic disorders, of which nephropathic cystinosis is the most common. The disease is caused by mutations in the CTNS gene, encoding the lysosomal cystine transporter cystinosin, and is characterized by accumulation of cystine in the lysosomes throughout the body. In the majority of the patients, this leads to generalized proximal tubular dysfunction (also called DeToni-Debre-Fanconi syndrome) in the first year and progressive renal failure during the first decade. Extrarenal organs are affected by cystinosis as well, with clinical symptoms manifesting mostly after 10 yr of age. The cystine-depleting agent cysteamine significantly improves life expectancy of patients with cystinosis, but offers no cure, pointing to the complexity of the disease mechanism. In this review, current knowledge on the pathogenesis of cystinosis is described and placed in perspective of future research.1 november 201