Primary Hyperoxaluria

Primary hyperoxaluria is a rare condition characterized by the overproduction of a substance called oxalate (also called oxalic acid). In the kidneys, the excess oxalate combines with calcium to form calcium oxalate, a hard compound that is the main component of kidney stones. Deposits of calcium oxalate can lead to kidney damage, kidney failure, and injury to other organs.

Primary hyperoxaluria is caused by the shortage (deficiency) of an enzyme that normally prevents the buildup of oxalate. There are two types of primary hyperoxaluria, distinguished by the enzyme that is deficient. People with type 1 primary hyperoxaluria have a shortage of a liver enzyme called alanine-glyoxylate aminotransferase (AGXT). Type 2 primary hyperoxaluria is characterized by a shortage of an enzyme called glyoxylate reductase/hydroxypyruvate reductase (GRHPR).

Type 1 primary hyperoxaluria is estimated to occur in 1 to 3 per million people; it is more common in some Mediterranean countries, such as Tunisia. Although the incidence of type 2 primary hyperoxaluria is unknown, it is less common than type 1.

Genes Related to Disorder

Mutations in the AGXT and GRHPR genes cause primary hyperoxaluria.The breakdown and processing of certain sugars and protein building blocks (amino acids) produces a substance called glyoxylate. Normally, glyoxylate is converted to the amino acid glycine or to a compound called glycolate through the action of two enzymes, alanine-glyoxylate aminotransferase and glyoxylate reductase/hydroxypyruvate reductase, respectively. Mutations in the AGXT or GRHPR gene cause a shortage of these enzymes, which prevents the conversion of glyoxylate to glycine or glycolate. As levels of glyoxylate build up, it is converted to oxalate. Oxalate combines with calcium to form calcium oxalate deposits, which can damage the kidneys and other organs.

This condition is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition.