Cystinosis and its renal complications in children

Nephropathic cystinosis [1–3] deserves a special place in the annals of clinical medicine as the first treatable lysosomal storage disease. The pathophysiology itself, based upon the formation of cystine crystals within the lysosomes of cells, is remarkable. The presence of cystine crystals provides a clue to the basic defect in cystinosis, i.e., failure to transport cystine out of lysosomes [4–6]. This created a new area of biomedical investigation, explained the lysosome’s function in salvaging small molecules for reutilization by the cell, and revealed a new category of lysosomal storage disorders due to transport defects rather than enzyme deficiencies [7]. Even more striking, a rational therapy of cystine depletion (i.e., cysteamine) emerged [8–10], transforming nephropathic cystinosis from a universally fatal disease to a treatable chronic disorder with a decent quality of life and increased life span. Today, physicians can even observe the gradual dissolution of cystine crystals by cysteamine eyedrops bathing the corneas of patients’ eyes [11–13].