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Primary hyperoxaluria type 2
Primary hyperoxaluria (PH) type 2 is a rare disorder of glyoxylate metabolism caused by the deficiency of the enzyme glyoxylate reductase/hydropyruvate reductase (GR/HPR) characterized by a childhood onset with clinical manifestations that include recurrent nephrolithiasis, nephrocalcinosis and end-stage renal disease with subsequent systemic oxalosis.
The prevalence is unknown. PH2 is rarer than PH1.
The onset of PH2 occurs typically in childhood. Clinical presenting manifestations include nephrolithiasis / urinary tract obstruction, hematuria, renal colic, but also possibly nephrocalcinosis and end-stage renal disease with systemic oxalosis; the latter two occur more commonly and earlier in primary hyperoxularia type 1 than in type 2.
PH2 is caused by mutations in the GRHPR gene (9q12), encoding the enzyme glyoxylate reductase/hydroxypyruvate reductase.
Clinical diagnosis may be confirmed by measuring urinary oxalate, urinary L-glycerate, kidney stone analysis, molecular genetic testing and sometimes by glyoxylate reductase enzyme activity from liver biopsy.
Other disorders that may present with a history of stone disease (and/or early stone formation) include primary hyperoxaluria type 1, primary hyperoxaluria type 3, Dent disease, primary renal tubular acidosis, cystinuria, xanthinuria, and adenine phosphoribosyltransferase deficiency (see these terms).
Prenatal genetic testing and preimplantation genetic diagnosis are possible for at-risk pregnancies and affected families.
PH2 is transmitted in an autosomal recessive manner. Genetic counseling and proband testing are recommended for an affected family.
Management and treatment
Daily management and early supportive measures are essential in maintaining renal function. Treatment aims at minimizing calcium oxalate deposition before advanced renal failure by maintaining a high urine output. In advanced stages, treatment may require renal transplantation and dialysis.
Prognosis, if left untreated, can be severe.