Primary hyperoxaluria

Primary hyperoxaluria
Specialty	Obstetrics and gynaecology, urology, medical genetics, endocrinology

Primary hyperoxaluria is a rare, inherited condition, resulting in increased excretion of oxalate, with oxalate stones being common. Hyperoxaluria refers to oxalate derived from dietary sources or that which is secondary to malabsorption. Primary hyperoxaluria, on the other hand, refers to a specific type of hyperoxaluria that is due to a metabolic defect resulting from a heritable genetic defect.

Pathophysiology

The buildup of oxalate in the body causes increased excretion of oxalate, which in turn results in renal and bladder stones. Stones cause urinary obstruction (often with severe and acute pain), secondary infection of urine and eventually kidney damage.

Oxalate stones in primary hyperoxaluria tend to be severe, resulting in relatively early kidney damage (say teenage, early adulthood), which impairs the excretion of oxalate leading to a further acceleration in accumulation of oxalate in the body.

After the development of renal failure patients may get deposits of oxalate in the bones, joints and bone marrow. Severe cases may develop haematological problems such as anaemia and thrombocytopaenia. The deposition of oxalate in the body is sometimes called "oxalosis" to be distinguished from "oxaluria" which refers to oxalate in the urine.

Renal failure is a serious complication requiring treatment in its own right. Dialysis can control renal failure but tends to be inadequate to dispose of excess oxalate. Renal transplant is more effective and this is the primary treatment of severe hyperoxaluria. Liver transplantation (often in addition to renal transplant) may be able to control the disease by correcting the metabolic defect.

In a proportion of patients with primary hyperoxaluria type 1 (about 5%), pyridoxine treatment (vitamin B6) may decrease oxalate excretion and prevent kidney stone formation.

Primary hyperoxaluria is an autosomal recessive disease, meaning both copies of the gene contain the mutation. Both parents must have one copy of this mutated gene to pass it on to their child, but they do not typically show signs or symptoms of the disease.

Classification

There are three main types of primary hyperoxaluria, each associated with specific metabolic defects. Type 1 is the most common and rapidly progressing form, accounting for about 80% of all cases. Type 2 and 3 account for about approximately 10% each of the population.

Type	OMIM	Gene
HP1	Template:OMIM2	AGXT
HP2	Template:OMIM2	GRHPR
HP3	Template:OMIM2	DHDPSL

Mutations in these genes cause a decreased production or activity of the proteins they make, which stops the normal breakdown of glyoxylate.

External links

• GeneReview/NCBI/NIH/UW entry on Primary Hyperoxaluria Type 1
• GeneReview/NCBI/NIH/UW entry on Primary Hyperoxaluria Type 2
• Primary hyperoxaluria (A service of the U.S. National Library of Medicine)