Overview of Hyperoxaluria
Kidney stones are on the rise. One cause is a condition called hyperoxaluria — when you have too much oxalate in your urine. Oxalate is a natural chemical in your body, and it’s also found in certain types of food. There is no known need for oxalate by the human body, it is normally eliminated as waste through the kidneys. But too much oxalate in your urine can cause serious problems when the excess oxalate binds with calcium in the urine to form kidney stones.
Hyperoxaluria can be caused by eating too many oxalate-rich foods, an intestinal disease or an inherited (genetic) disorder. In some persons the cause of the disease is not known, but may result from changes in the way kidneys handle normal amounts of body oxalate. Hyperoxaluria is uncommon, though can be found in about 20 percent of individuals with kidney stones. Quick diagnosis and treatment of hyperoxaluria is important to the long-term health of your kidneys.
Dietary hyperoxaluria. Eating a diet of high oxalate content foods can cause high levels of oxalate in the urine and can increase your risk of hyperoxaluria or kidney stones. Generally, if diet changes are made the urine oxalate will then decrease. Ask your doctor or dietitian for a list of high-oxalate foods.
Enteric hyperoxaluria. Several intestinal diseases, including Crohn’s disease and short bowel syndrome as a result of surgical procedures like Bariatric surgery may increase the absorption of oxalate from foods, which can then increase the amount of oxalate excreted in the urine. Avoiding, foods high in oxalate in particularily important.
Primary hyperoxaluria (PH). Is an inherited, autosomal recessive (genetic) condition. In this type, the liver doesn’t create enough of a certain protein (enzyme) that prevents overproduction of oxalate, or the enzyme doesn’t work properly. Unlike dietary or enteric hyperoxaluria, the amount of oxalate in the urine is not greatly affected by changes in dietary oxalate.
Types of PH
PH is a rare, occuring in one to three people out of a million. It may be found among all ages, from infants to late adulthood. Three types of PH are currently known and can be readily diagnosed. Each of the types of PH causes a decrease in activity of a specific enzyme in the liver which causes an increase in oxalate production. The decrease in the enzyme activity in each case changes how the liver makes oxalate, and a much larger amount of oxalate is produced.
The enzymes involved in the three disorders are as follows:
PH1: alanine-glyoxylate aminotransferase, or AGT
PH2: glyoxylate/hydroxypyruvate reductase, or GR/HPR
PH3: 4-hydroxy-2-oxoglutarate aldolase, or HOGA
Very large amounts of oxalate are produced when there is not enough of these enzymes in the liver. Excess oxalate is eliminated through your kidneys, in your urine. The extra oxalate can combine with calcium to create kidney stones and crystals, which can damage the kidneys and cause them to stop working (renal failure).
It is possible that other types of PH will be discovered. Some patients have high urine oxalates and kidney stones but do not have a genetic mutation that causes one of the three known types of PH. Future research may help us to better understand the cause of the high urine oxalate in these patients.
Oxalosis can occur when the kidneys stop working and can no longer eliminate the high levels of oxalate that can occur in PH. Oxalate levels in the blood begin to rise and the oxalate can spread to eyes, bones, skin, muscles, heart and other major organs. If left untreated, PH can lead to serious illness and even death. Among patients with PH1, about 50 percent will have kidney failure by age 30-35 years. Kidney failure happens less often in patients with PH2 but still occurs and is still unknown in patients with PH3. For that reason, it is critical that PH be diagnosed and treated as early as possible. Patients most often develop the first symptoms, typically kidney stones from birth to the mid-20s but PH can be diagnosed late into adulthood. In some patients the first symptom is kidney failure.