Types of Stones

Hyperoxaluria

Hyperoxaluria from various causes results in the deposition of insoluble calcium oxalate crystals in the kidney producing nephrocalcinosis and stone formation.

Primary (Inherited) Hyperoxaluria
Primary hyperoxaluria type 1 (PH1) is a rare autosomal recessive disease caused by a deficiency of alanine: glyoxylate aminotransferase (AGT). In this condition, hepatic overproduction of oxalate occurs. The vast majority of families with PH1 show a horizontal autosomal recessive pattern of inheritance. Treatment should include pyridoxine (Vitamin B6) and magnesium supplementation as well as orthophosphate.

In primary hyperoxaluria, type 2 (PH2), there is a deficiency of the enzyme D-glycerate dehydrogenase/glyoxylate reductase. In contrast to PH1, in which patient's progress to end stage renal failure (ESRF) due to severe, bilateral nephrocalcinosis, patients with PH2 typically present with nephrolithiasis without ESRF. The treatment of PH2 is mainly supportive. Unlike the benefits seen with vitamin B6 therapy for the pyridoxine-sensitive patients with PH1, there is no effect in PH2 patients.

Suggested readings
Rumi LA, Pearle MS, Pak CYC. Medical therapy: Calcium oxalate urolithiasis. Urol Clin North Am 1997, 24:1:117-133.

Hoppe B, Danpure CJ, Rumsby G, Fryer P, Jennings PR, Blau N, Schubiger G, Neuhaus T, Leumann E. A vertical (pseudodominant) pattern of inheritance in the autosomal recessive disease primary hyperoxaluria type 1: Lack of relationship between genotype, enzymic phenotype, and disease severity. Amer J Kidney Diseases 1007, 29: 1: 36-44.

Kemper MJ, Mullerwiefel DE. Nephrocalcinosis in a patient with primary hyperoxaluria type 2. Pediatr Nephrol 1996, 10:4:442-444.

Enteric Hyperoxaluria
Intestinal disease (malabsorption or short bowel syndrome) is the most common cause of hyperoxaluria. Reduced availability of free calcium to bind intestinal oxalate occurs in malabsorption. The colon absorbs unbound oxalate. Other putative mechanisms include increased colonic permeability and a decrease in Oxalobacter formigenes (oxalate-degrading bacteria. Treatment includes calcium citrate supplementation to bind intestinal oxalate and magnesium and Vitamin B6 supplementation.

Suggested readings
Rumi LA, Pearle MS, Pak CYC. Medical therapy: Calcium oxalate urolithiasis. Urol Clin North Am 1997, 24:1:117-133.

Idiopathic Hyperoxaluria
In this group of patients, the hyperoxaluria is generally mild. Treatment consists of hydration and avoidance of foods containing. If a low oxalate diet with adequate calcium intake does not normalize urinary oxalate levels, Vitamin B6 may be added.

The increase oxalate excretion in very low birth weight infants (VLBW) is responsible for the high incidence of nephrocalcinosis and nephrolithiasis in this group of patients. A spot urine for oxalate/creatinine ratio is suitable for screening VLBW infants.

Suggested readings
Rumi LA, Pearle MS, Pak CYC. Medical therapy: Calcium oxalate urolithiasis. Urol Clin North Am 1997, 24:1:117-133.

Sonntag J, Schaub J. The identification of hyperoxaluria in very low-birthweight infants-Which urine sampling method? Pediatr Nephrol 1997, 11:2:205-207.

 

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