What Is Primary Hyperoxaluria Type 2?
Primary hyperoxaluria type 2 (PH2), caused by mutations in the GRHPR gene, is an inherited disease in which the lack of a particular liver enzyme causes the body to accumulate excess amounts of a substance called oxalate. This oxalate leads to a buildup of insoluble calcium salts in the kidneys and other organs, resulting in progressive organ damage. The disease has similar symptoms to primary hyperoxaluria type 1 (PH1), but PH2 tends to be a less-aggressive form of the disease, even when symptoms start early in life. PH1 and PH2 are caused by different missing liver enzymes.
Symptoms of PH2 typically begin in childhood. Affected individuals are prone to recurrent kidney stones that can lead to kidney failure; however, when this occurs, it is usually later in life. Deposits in the urinary tract can lead to difficulty with urination, blood in the urine, and recurrent urinary tract infections. In addition, PH2 also leaves insoluble calcium deposits in other body tissues that may cause problems with bones, eyes, teeth, nerves, and the heart.
How Common Is Primary Hyperoxaluria Type 2?
The prevalence of PH2 is unknown.
How Is Primary Hyperoxaluria Type 2 Treated?
Treatments for PH2 are aimed at preventing the formation and deposition of calcium oxalate. Increased fluid intake is extremely important. Calcium-oxalate crystallization inhibitors (i.e., potassium or sodium citrate, orthophosphate, and magnesium) and dietary interventions may be recommended.
While individuals with PH2 are less likely to develop kidney failure than those with PH1, organ transplantation remains an option if kidney failure does occur. Because a deficient liver enzyme leads to kidney failure, early liver transplantation may avoid the need to also transplant new kidneys; however, combined liver and kidney transplantation has never yet been used for PH2. Kidney replacement alone is not a sufficient treatment, as the byproducts of the liver could destroy the new kidneys as well.
Individuals with PH2 should avoid extremely large doses of vitamin C as well as foods high in oxalate, including chocolate, rhubarb, and starfruit.
What Is the Prognosis for an Individual with Primary Hyperoxaluria Type 2?
The prognosis for an individual with PH2 is variable and depends on how early the disease is detected and treated. For some individuals with the disease, hydration and medication will be sufficient to control the disease. In other cases, affected individuals will develop kidney failure that may require kidney transplantation. As with PH1, recurrence of calcium deposits has been reported. Generally, individuals with PH2 have a better long-term outcome than those with PH1, and they require fewer surgeries.