Extrarenal complications of cystinosis.

Cystinosis is a rare autosomal recessive disease with an incidence 1 per 100,000-200,000 live births. It is caused by pathogenic variants of the cystinosin (CTNS) gene that lead to impaired cystine transport from lysosomes to cystosol, resulting in cystine accumulation in lysosomes and subsequent cellular dysfunction. The initial manifestation, cystine accumulation in proximal tubular cells (PTCs), causes renal Fanconi syndrome, which presents with proximal renal tubular acidosis and generalized dysfunction of the proximal tubule, including the presence of polyuria, glycosuria, phosphaturia, aminoaciduria, tubular proteinuria, growth retardation, and rickets. Eventually, glomerular involvement, glomerular proteinuria, focal segmental glomerulosclerosis (FSGS), and progression to kidney failure occur. Although the kidneys are the first organs affected, and play a key role in morbidity and mortality, extrarenal multiorgan involvement can occur in patients with cystinosis, which is seen not only in adults but in early ages in untreated patients, patients with insufficient treatment, and in those that don't comply with treatment. The treatment of cystinosis consists of supportive treatment for Fanconi syndrome, and specific lifelong cystine-depleting therapy using oral cysteamine. There is strong evidence that as early as possible, initiation and ongoing appropriate therapy with cysteamine are essential for delaying the progression to kidney failure, end-organ damage, and extrarenal involvement. The present review aimed to evaluate the extra renal complications of cystinosis.