Epidemiological aspects of renal stone diseaseRenal stone disease is common in the population with a life time risk between 10 and 20% for males and 3-5% for females. Approximately 50% of unselected stone formers will experience stone recurrence within ten years. Recurrences are particular common in individuals with early onset of the disease and in those with a family history of renal stones (33). A high urinary excretion of calcium, oxalate, uric acid, a high urinary pH, a low urinary volume and low urinary excretion of glycosaminoglycans are risk factors for stone formation and a combination of these risk factors will ultimately define the risk of forming stone (42). The renal stone disease has been proposed to be largely a disease of the affluent society (42).
Physico-chemical aspectsThe main part of the stones formed in the kidneys are composed of calcium oxalate, calcium phosphate or a mixture of both. Currently there are three main theories of probable importance in the formation of renal calcium stones: a) the concentration of precipitating substances, mainly calcium, oxalate and phosphate and the solibility of the mineral phace formed; b) the role of urinary promotors of crystallization and crystal aggregation in the urine and c) the role of inhibitors of crystallization and crystal aggregation (14).The urine from most stone formers is supersaturated with respect to calcium oxalate or cald-um phosphate. As the degree of supersaturation varies there is a great overlap between stone formers and none-stone forming subjects. Much attention has been directed to distinguish between these two groups. Subjects without renal stone disease excrete no or only individual crystals in the urine whereas stone formers excrete greater amounts of crystals and, in addition, tend to excrete large aggregations of crystals (41). The main inhibitors of the crystal formation of calcium oxalate and calcium phosphate are citrate, pyrophosphate and magnesium, whereas glycosaminoglucans besides citrate and pyrophosphate play the primary role for inhibiting the aggretion of formed crystals in the urine (14).Already in 1929 Greta Hammarsten indicated that magnesium increased the solibility of calcium oxalate in vitro (18). Others have shown that magnesium decreases the incidence of experimental, calcium oxalate stone formation (4, 15, 43). Desmars and Tawashi (8) emphasized the fine kinetic control magnesium exerts on calcium oxalate formation, because of the greater solibility product of magnesium oxalate compared to that of calcium oxalate.The difficulty in evaluation of results obtained from diluted urine is well illustrated by the fact that pyrophosphate has been shown to be the main inhibitor of calcium phosphate crystal formation when measured in 2% urine, whereas pyrophosphate only accounts for about 10% of the inhibitory activity in whole urine (3). This quantitative technique to determine the inhibitors of calcium phosphate precipitation in whole, undiluted urine, demonstrated that magnesium represents 20% of the total inhib...