Cystinuria

Cystinuria, the excretion of cystine (see) in urine in the form of crystals or amorphous granules. C. can be observed as a symptom of severe liver lesions (e.g., acute atrophy) or as a manifestation of a particular disorder of intermediate protein metabolism, as an independent disease. At the same time, in the urine of cystinurics, the excretion of inorganic sulfates and neutral sulfur decreases, since both originate from the sulfur-containing amino acids cystine and cysteine, which are formed endogenously or ingested with food. The pathogenesis of C. to this day appears to be insufficiently clarified. Experiments with large loads of cysteine compounds show that in cystinurics, the formation of bile acids from cystine is not impaired, and apparently the issue is a slowing down of deamination processes and the restoration of sulfur-containing cystine, cysteine compounds into organic acids and sulfates. The described disorders of intermediate metabolism are apparently quite deep and are undoubtedly connected with hereditary peculiarities in subjects affected by this disease, since they have repeatedly been observed in many members of the same family. Clinically, mildly expressed and more severe forms of C. are distinguished. The manifestation of the disease is not characteristic: the symptoms of the disease can become more severe if the poorly soluble cystine, precipitating, forms crystal conglomerates and stones. In the latter case, patients suffer from typical kidney stone or bladder stone disease and subsequently may experience repeated attacks of stone disease. Since the formation of stones in cystinurics is by no means necessary, Lichtwicz expressed the opinion that the appearance of stones is a symptom of the disruption of protective colloids (see Kidney Stone Disease). The treatment of C. is mainly dietetic: reducing the amount of protein introduced to 1 g or less per 1 kg of weight narrows the possibilities for exogenously caused C., however, it is hardly possible to affect the very essence of the process and its most often hereditarily conditioned pathogenetic mechanisms to any extent.