What is the definition of Primary Hyperoxaluria Type 1?
Primary hyperoxaluria type 1 (PH1) is a rare disorder that mainly affects the kidneys. It results from buildup of a substance called oxalate, which normally is filtered through the kidneys and excreted in the urine. In people with PH1, the accumulated oxalate is deposited in the kidneys and urinary tract. It combines with calcium, forming the main component of kidney and bladder stones (calcium oxalate).
Signs and symptoms of PH1 vary in severity and may begin any time from infancy to early adulthood. Symptoms may include recurrent kidney stones; blood in the urine; and urinary tract infections. Left untreated, PH1 can result in end-stage renal disease, which is life-threatening.
PH1 is due to mutations in a gene called AGXT. Inheritance is autosomal recessive.
Early treatment is important for maintaining kidney function. Each person's treatment plan depends on his/her symptoms and the severity of the condition. Management may involve high fluid intake; vitamin B6 (pyridoxine); calcium-oxalate crystallization inhibitors (citrate, pyrophosphate, and magnesium); kidney stone therapies; and dialysis in some cases. Liver and/or kidney transplantation may be needed.
What are the alternative names for Primary Hyperoxaluria Type 1?
- Oxalosis 1
- Glycolic aciduria
- Alanine-glyoxylate aminotransferase deficiency
- Peroxisomal alanine glyoxylate aminotransferase deficiency
- Hepatic AGT deficiency
- Serine pyruvate aminotransferase deficiency
What are the causes for Primary Hyperoxaluria Type 1?
Primary hyperoxaluria type 1 is caused by mutations in a gene called AGXT. This gene gives the body instructions for making an enzyme called alanine-glyoxylate aminotransferase. This enzyme is found in cell structures called peroxisomes in liver cells. It converts a compound called glyoxylate to the amino acid glycine.
Mutations in the AGXT gene lead to a decrease in the amount or function of the enzyme, preventing the breakdown of glyoxylate. This is turn causes glyoxylate to accumulate, and it is converted to oxalate instead of glycine. Excess oxalate that is not excreted from the body then combines with calcium to form calcium oxalate, which damages the kidneys and other organs.
What are the symptoms for Primary Hyperoxaluria Type 1?
The symptoms and severity of primary hyperoxaluria type 1 (PH1) can vary. The age that symptoms begin ranges from birth to the sixth decade of life (although there are exceptions). About 19% of people with PH1 have a severe, very early-onset form that becomes apparent within a few months after birth. At the milder end of the spectrum, some people with PH1 go without any symptoms for over 40 or 50 years. The median age of onset is about 5-6 years.
Features of renal involvement can range from nephrocalcinosis and renal failure in infancy, to only occasional stones diagnosed in adulthood. Kidney stones are commonly the first sign of hyperoxaluria. Symptoms of kidney stones can include sudden abdominal or flank pain; blood in the urine; frequent urge to urinate; pain while urinating; or fever and chills.
Untreated PH1 leads to kidney failure, which is life-threatening. Symptoms of kidney failure can include decreased or no urine output; feeling ill or tired; loss of appetite; nausea and vomiting; and pale skin due to anemia.
What are the current treatments for Primary Hyperoxaluria Type 1?
The goal of treatment for primary hyperoxaluria type 1 (PH1) is to minimize calcium oxalate deposition and maintain renal function. Early diagnosis and prompt therapy is critical to preserve the function of the kidneys for as long as possible.
General therapies for preventing kidney stones benefit all people with PH1. Recommendations for this include:
- drinking large amounts of fluid
- oral potassium citrate to inhibit calcium oxalate crystallization
- drugs such as thiazides to decrease calcium in the urine
- avoiding significant intake of vitamin C or D (they promote stone formation)
- supplementation of dietary calcium
Treatment for kidney stones may involve shock wave lithotripsy, percutaneous nephrolithotomy, and/or ureteroscopy.
Reducing the body's production of oxalate involves treatment with pyridoxine. While only about 10%-30% of people with PH1 respond to treatment with pyridoxine, it has been recommended that all people with PH1 receive a minimum 3-month trial at the time of initial diagnosis.
Dialysis to remove oxalate in people with PH1 has limitations, but may be indicated in specific circumstances in some people with PH1.
Lastly, organ transplantation is an option for therapy. There has been much discussion among experts regarding the best transplantation strategy for people with PH1. Depending on each person's response to other therapies and the disease severity, options may include combined liver-kidney transplant; sequential liver-kidney transplant; an isolated kidney transplant, or an isolated liver transplant.
Other therapies for PH1 are under investigation and may become options for people with PH1 in the future.
People with questions about the treatment of PH1 for themselves or family members should speak with their doctor for treatment options and advice.
What is the outlook (prognosis) for Primary Hyperoxaluria Type 1?
The progression and severity of primary hyperoxaluria type 1 (PH1) varies. Specific mutations in the responsible gene (AGXT) may correspond with particular symptoms, disease progression, and response to treatment. For example, some people with PH1 respond to treatment with vitamin B6 (pyridoxine), while others do not. Some research suggests that specific mutations in the AGXT gene are associated with later onset end stage renal failure.
The outlook is very poor if PH1 is left untreated. An early and accurate diagnosis leading to aggressive supportive treatment is a major factor in short- and long-term outcomes. In the future, the prognosis may be improved by new therapies.
Is Primary Hyperoxaluria Type 1 an inherited disorder?
Primary hyperoxaluria type 1 is inherited in an autosomal recessive manner. This means that to be affected, a person must have a mutation in both copies of the responsible gene in each cell. Affected people inherit one mutated copy of the gene from each parent, who is referred to as a carrier. Carriers of an autosomal recessive condition typically do not have any signs or symptoms (they are unaffected). When 2 carriers of an autosomal recessive condition have children, each child has a:
- 25% chance to be affected
- 50% chance to be an unaffected carrier like each parent
- 25% chance to be unaffected and not a carrier