23 PH type II is somewhat milder compared with PH type I but is not benign. Recently, a third variant, PH type III has been described in 8 families with hyperoxaluria and mutations in the DHDPSL gene. 24 The exact mechanism by which hyperoxaluria occurs in PH type III is yet to be fully elucidated. In secondary

hyperoxaluria, there is either a dietary exposure to large amounts of oxalate (or oxalate precursors) or an underlying disorder that causes increased absorption of dietary oxalic acid from the intestinal tract. Gastrointestinal absorption varies inversely with dietary calcium intake, and, as a result, calcium-deficient diets may increase oxalate absorption and hyperoxaluria.25 Oxalate is a byproduct ICG-001 of ascorbic acid metabolism, and high doses of vitamin C have also been associated with hyperoxaluria.

Increased dietary absorption is usually characterized by fat malabsorption or a chronic diarrheal disorder. Among secondary causes of hyperoxaluria, those attributable to gastrointestinal disease are inflammatory bowel disease, celiac disease, exocrine pancreatic insufficiency (cystic fibrosis), biliary tract disease, and small bowel resection or short bowel syndrome. The pathogenesis in these conditions results from the presence of free fatty acids that bind calcium in the intestinal lumen resulting in more unbound oxalate, which is free to be absorbed. Citrate is normally present in the urine and regulated through a process of both absorption and metabolism at the learn more level of the proximal tubule. Hypocitraturia is generally defined as a citrate to creatinine ratio of less than 180 mg/gm in men and less than 300 mg/gm in women on a 24-hour collection (see Table 1). Intracellular acidosis of the proximal tubule, caused by either metabolic acidosis

or hypokalemia results in an increased PDK4 citrate absorption in the proximal tubule and resultant hypocitraturia. As a result, the ketogenic diet, certain medications (topiramate, zonisamide, and acetazolamide), dRTA, and chronic diarrhea are commonly associated with hypocitraturia. Given that an incomplete dRTA can occur in the absence of an overt systemic acidosis or hypokalemia, the condition can often be overlooked in the face of hypocitraturia if provocative acid-load testing is not readily available. Despite these known associations, most cases of hypocitraturia are idiopathic although a diet rich in animal protein and low in vegetable fiber and potassium seems to promote lower citrate excretion.26 and 27 Cystinuria is an autosomal recessive disorder caused by mutations in either the SLC3A1 or the SLC7A9 genes, resulting in a disordered amino acid transport in the proximal tubule, 28 Cystinuria is characterized by urinary hyperexcretion of cystine and the dibasic amino acids lysine, ornithine, and arginine. Normal individuals excrete less than 50–60 mg of cystine/d/1.