Hyperoxaluria

Primary hyperoxaluria type 1 is a rare progressive genetic disease with clinical manifestations due to the hepatic oxalate production.

PH1 metabolic defect results from a deficiency of liver specific peroxisomal enzyme alanine-glyoxalate aminotransferase AGT)  which converts the oxalate precursor glyoxalate to glycine.

With absent or deficient AGT glyoxalateis oxidize to oxalate, increasing plasma oxalate levels.

Liver produced oxalate is excreted primarily by the kidneys and the toxic mediator of end organ damage in PH1.

PH1 commonly presents in childhood with kidney stones, end-stage kidney disease or systemic disease where oxalate is deposited in the bone, retina, heart, and skin.

Diagnosis is often delayed four years with result high incidence of end-stage kidney disease and death.

In PH1 progression to end-stage kidney disease is related to urinary oxalate levels.

Patients require renal and liver transplantation.

Kidney stones presenting symptom in most cases.

Common after Roux-en-Y gastric bypass surgery, and can lead to a spectrum of kidney diseases including calcium oxalate kidney stones, acute renal failure, chronic kidney disease, and ultimately end-stage renal disease with unrecognized hyperoxaluria

In hyperoxaliria, excess oxalate binds to calcium, forming insoluble calcium oxalate stones that are deposited in the renal tubules and urinary tract and more distant tissues.

Most cases of primary hyperoxaluria are associated with variants in 1 of 3 genes AGXT, GRHPR, and HOG1 in disease types one, two, and three, respectively that encode for enzymes involving glyoxalate metabolism.

More than 200 different pathogenic variants have been described.

The gene defect are autosomal recessive all resulting in increased oxalate production.

Secondary hyperoxaluria is caused by increased oxalate absorption from the intestine or excessive dietary intake of oxalate such as with rhubarb, spinach, parsley, and cocoa or its precursor ascorbic acid.

In secondary hyperoxaluria which occurs with excessive intake of oxalate in chronic renal disease.

Cutaneous lesions are unusual in secondary hyperoxaluria.

skin lesions in primary hyperoxaluria include purpura, livid reticularis, acrocyanosis and peripheral gangrene.

Ascorbic acid increases the risk of plasma calcium oxalate supersaturation, particularly among patients undergoing hemodialysis.

Increased intestinal oxalate absorption in most commonly caused by fat malabsorption, as in inflammatory bowel disease patients who have undergone Roux-en-Y gastric bypass.

Normally oxalate binds preferentially to calcium in the gut, forming insoluble calcium salts that are excreted in the stool.

When there is malabsorption, excessive excess fatty acids complete for calcium binding, leaving increased levels of unbound oxalate to be absorbed in the intestine.

Primary hyperoxaluria associated with systemic deposition of calcium oxalate and is associated with heart block, synovitis, oxalate osteopathy, or crystalline retinopathy.

Secondary hyperoxaluria tends to follow a more benign course.

Measurement of two 24 hour urine specimens is recommended to confirm the diagnosis of hyperoxaluria.

Values greater than 1 mmol per 24 hours characterize primary hyperoxaluria, where as less marked elevation is more typical of secondary hyperoxaluria.

In patients with chronic kidney disease, 24 hour urine testing is less sensitive because of deterioration in renal function leads to reduced urinary oxalate excretion.

Plasma oxalate levels in the normal range or 1-5 micro moles per liter, plasma oxalate levels are often higher than 80 µmol believer in patients with primary hyperoxaluria and between 20 and 80 µmol, in patients with secondary hyperoxaluria.

A diagnosis of primary hyperoxaluria may be confirmed by gene sequencing of a GXT, GRHPR, and HOGA1.

Primary hyperoxaluria is associated with elevated urinary levels of glycolate.

Treatment of secondary hyperoxaluria typically involves high fluid intake of 3-4 L per day to counteracts calcium oxalate supersaturation, as well as dietary modification of high calcium and low oxalate diet.

Treatment options Include hyperhydration, high-dose pyridoxine, and calcium oxalate crystallization Inhibitors, such as citrate which may decrease the incidence of kidney stones and slow disease progression.

Patients with may benefit from pyridoxine.

Patients with advanced disease receive hemodialysis.

Liver transplantation  or liver/kidney transplantation can cure the metabolic defect in primary hyperoxaluria , can normalize oxalate levels, improve disease manifestations and prevent progression to end-stage kidney disease.