NORD gratefully acknowledges Colin White, MD, FRCPC, Clinical Associate Professor of Pediatrics, University of British Columbia, Director of Dialysis, Fellowship Program Director, BC Children's Hospital, and M. B. Coulter-Mackie, PhD, Associate Professor Emerita, Department of Pediatrics, University of British Columbia, for assistance in the preparation of this report.
Primary hyperoxalurias (PHs) are a group of rare genetic metabolic disorders that are characterized by the accumulation of a substance known as oxalate in the kidneys and other organ systems of the body. Affected individuals lack functional levels of a specific enzyme that normally prevents the accumulation of oxalate. There are three main types of PH differentiated by the specific enzyme that is deficient. In the kidneys, excess oxalate binds with calcium to form a hard compound (calcium oxalate) that is the main component of kidney and urinary stones. Common symptoms include the formation of stones throughout the urinary tract (urolithiasis) and kidneys (nephrolithiasis) and progressively increased levels of calcium in the kidneys (nephrocalcinosis), although this last finding has not been identified in individuals with PH type III as of yet. Chronic, recurrent stone formation and the accumulation of calcium oxalate in kidney tissue can cause chronic kidney disease, which can ultimately progress to kidney failure (end stage renal disease [ESRD]). Eventually, kidney function can deteriorate to the point where oxalate begins to accumulate in other organ systems. Overall, the symptoms and severity of PH may vary greatly from one person to another. Chronic kidney disease and ESRD may already be present when a diagnosis is first made. PH is a treatable disorder and complications may be minimized with early recognition and prompt treatment.
PH type I is caused by mutations in the AGXT gene. PH type II is caused by mutations in the GRHPR gene. PH type III is caused by mutations in the HOGA gene (formerly known as the DHDPSL gene). The genetic mutations that cause PH are inherited as autosomal recessive traits.
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