inborn error of metabolism resulting in the deposition of crystals of the amino acid cystine in various body tissues. Tissues that are particularly affected include the bone marrow, liver, cornea (where the crystals can be seen), and kidney. When they are about six to nine months old, infants with cystinosis refuse to eat, grow poorly, and urinate excessively; these symptoms are related to more severe aspects of the disorder, which include rickets, enlargement of the liver, stunted growth, and kidney malfunction. The crystal deposits in the kidney tubules lead eventually to a full-blown manifestation of Fanconi syndrome (de Toni–Fanconi syndrome) (see de Toni-Fanconi syndrome (de Toni–Fanconi syndrome)), characterized by a generalized defect in the reabsorption of all amino acids, sugar, salts, and water. The specific genetic defect responsible for cystinosis is not known.