Idiopathic hyperuricemia does not mandate therapy. A pronounced increase in uric acid production, enhanced uricosuria, uric acid lithiasis and acute renal insufficiency are well described entities in myeloproliferative disorders where there is rapid tissue turnover. During chemotherapy and radiation therapy the incidence of this entity peaks. Judicious hydration, urine alkalinization and xanthine oxidase inhibitor therapy can obviate these problems in most instances. Its pattern of inheritence is autosomal recessive.
Cystine is produced endogenously from the metabolism of dietary methionine.
Cystine, together with other anuno acids is filtered at the level of the glomerulus and the bulk is reabsorbed at the level of the proximal tubule. Secretion pathways for cystine from the periceHular capillaries into the cell and ultimately into the urine also exist. The different cystine transport pathways at the level of the renal proximal tubule are illustrated in Fig. 9. A common pathway exists for cystine, lysine, arginine and ornithine and all four amino acids are therefore not absorbed. However, cystine is least soluble of these amino acids and it alone is pathogenic.