DiagnosisClinical Diagnosis Primary hyperoxaluria type 2 (PH2) is caused by deficiency of the enzyme glyoxylate reductase/hydroxypyruvate reductase (GR/HPR). While clinical features (urinary tract symptoms or findings such as renal colic, kidney failure, urinary tract infection, hematuria, and/or obstruction of the urinary tract) may overlap with other causes of kidney stone formation, a clinical diagnosis of PH2 should be suspected if significant hyperoxaluria and coincident L-glyceric aciduria are present (see Testing). TestingBiochemical testing Urinary oxalate. Urinary oxalate can be measured in either a random or 24-hour collection of urine (designated 24h). Note: Because random ratios are subject to prandial variability, a timed collection is preferable if it can be obtained.Urinary oxalate excretion in PH2 is typically greater than 0.7 mmol/1.73 m²/24h [Milliner 2005] although lesser increases may be observed. Normal urinary oxalate excretion is less than 0.46 mmol/1.73 m²/24hUrinary L-glycerate. Although the presence of L-glycerate in the urine is regarded as pathognomonic for PH2 and the majority of affected individuals exhibit L-glyceric aciduria (8/8 in the series of Chlebeck et al [1994]), exceptions are reported [Rumsby et al 2001].Kidney stone analysis. Kidney stones containing 100% calcium oxalate are supportive, but not diagnostic, of PH2.Plasma oxalate. After the onset of renal failure, measurement of plasma oxalate concentration may be helpful. In contrast to plasma oxalate concentrations in persons with renal failure from other causes, plasma oxalate concentrations in individuals with primary hyperoxaluria with glomerular filtration rate lower than 20 mL/min/1.73 m² often exceed 50 μmol/L. Glyoxylate reductase (GR) enzyme activity. Definitive diagnosis of PH2 requires measurement of glyoxylate reductase enzyme activity in a liver biopsy [Giafi & Rumsby 1998] or molecular genetic testing of GRHPR (see Molecular Genetic Testing).
Note: The enzyme has also been shown to be expressed in leukocytes [Knight et al 2006]; however, because of questions about the expression of the gene in leukocytes [Bhat et al 2005], measurement of enzyme activity in liver biopsy rather than leukocytes is recommended for diagnosis [Author, personal observation]. Molecular Genetic Testing Gene. GRHPR (previously known as GLXR), encoding glyoxylate reductase/ hydroxypyruvate reductase, is the only gene in which mutations are known to cause primary hyperoxaluria type 2.Clinical testingSequence analysis. A two-tiered approach can be used:Tier 1. Sequence analysis of exon 2 and exon 4 to detect the two commonly occurring mutations:c.103delG in exon 2, which accounts for approximately 37% of mutant alleles [Cregeen et al 2003]. It is possible to make a diagnosis (i.e., two mutations detected) in approximately 33% of individuals with liver biopsy-proven PH2 by testing for this mutation only [Rumsby et al 2004]. To date, this mutation has mainly been restricted to individuals of Northern European ancestry. c.403_404+2 delAAGT in exon 4, a four-base pair deletion, accounts for approximately 16% of disease alleles from individuals of predominantly Asian origin [Cregeen et al 2003; Rumsby, unpublished observations].Tier 2. Full gene sequencing. PCR amplification of genomic DNA with sequencing of individual exons and intron-exon boundaries has identified to date a total of 24 mutations [Cramer et al 1999; Webster et al 2000; Cregeen et al 2003; Booth et al 2006; Takayama et al 2007; Levin-Iaina et al 2009; Williams and Rumsby, unpublished]. Information on specific allelic variants may be available in Molecular Genetics (see Table A. Genes and Diseases and/or Pathologic allelic variants). Linkage analysis. Closely linked microsatellite markers have been identified for GRHPR [Webster et al 2000, Johnson et al 2002] including one in intron 8 [Cregeen et al 2003]. These markers have been useful for the exclusion of disease in other family members (e.g., asymptomatic young sibs of an affected individual) and for the identification of carriers when the causative mutations of the affected individual have not been identified [Johnson et al 2002]; in both instances linkage results were confirmed subsequently by identification of the causative mutation [Rumsby 2005].Table 1. Summary of Molecular Genetic Testing Used in Primary Hyperoxaluria Type 2 View in own windowGene Symbol Test MethodMutations DetectedMutation Detection Frequency by Test Method ^{1Test AvailabilityGRHPRSequence analysisSequence variants 2>99%Clinical1. The ability of the test method used to detect a mutation that is present in the indicated gene2. Examples of mutations detected by sequence analysis may include small intragenic deletions/insertions and missense, nonsense, and splice site mutations; typically, exonic or whole-gene deletions/duplications are not detected.Interpretation of test results. For issues to consider in interpretation of sequence analysis results, click here.Testing Strategy To confirm/establish the diagnosis in a proband. An evidence-based guideline for the diagnosis of primary hyperoxaluria type 1 (PH1) and primary hyperoxaluria type 2 (PH2) has been developed [Milliner 2005]. Because PH1 is more common than PH2, testing is first focused on the diagnosis of PH1 unless additional information (e.g., elevated urinary L-glycerate) suggests diagnosis of PH2. In an individual with persistently elevated urinary oxalate (>0.7 mmol/1.73 m2/24h) and either of the following:Normal renal function, no excessive dietary oxalate intake, and no gastrointestinal disease Renal failure with an elevated plasma oxalate concentration (>20 μmol/L at GFR<30 mL/min/1.73 m2, >50 μmol/L in ESRF) The following investigations are recommended:Sequence analysis of exons 2 and 4 to look for the common mutations c.103delG and c.403_404+2 delAAGT If two known mutations are found, a diagnosis of PH2 is made.If only one or no mutation is found, perform sequence analysis of the rest of the gene to look for other sequence variants. If only one mutation is found after sequencing the whole gene, perform a liver biopsy to measure glyoxylate reductase enzyme activity to confirm or exclude a diagnosis of PH2.If no mutations are found and normal glyoxylate reductase enzyme activity on liver biopsy, diagnoses such as PH1 or PH3 should be considered.Carrier testing for at-risk relatives requires either prior identification of the disease-causing mutations in the family or, if the mutations are not known, linkage analysis once the diagnosis of PH2 is certain in the proband.Note: Carriers are heterozygotes for this autosomal recessive disorder and are not at risk of developing the disorder.Predictive testing for at-risk asymptomatic family members requires prior identification of the disease-causing mutations in the family.Prenatal diagnosis and preimplantation genetic diagnosis (PGD) for at-risk pregnancies require prior identification of the disease-causing mutations in the family.Genetically Related (Allelic) Disorders No other phenotypes are known to be associated with mutations in GRHPR.}

Natural History The age of onset of primary hyperoxaluria type 2 (PH2) is typically in childhood [Milliner et al 2001, Johnson et al 2002], with those diagnosed in later life often relating symptoms from childhood [Rumsby et al 2001, Takayama et al 2007]. As in PH1, establishing the diagnosis is often delayed, sometimes even for years.Presenting symptoms are typically those associated with the presence of renal stones including hematuria, renal colic, or obstruction of the urinary tract [Johnson et al 2002]. Affected individuals may also present with nephrocalcinosis or end-stage renal disease (ESRD).The majority of individuals have renal stones composed of calcium oxalate [Milliner et al 2001, Johnson et al 2002]. Nephrocalcinosis, observed on ultrasound examination, abdominal x-ray, or CT examination, is a much less common finding in PH2 than in PH1, having been described in one individual [Kemper & Müller-Wiefel 1996]. The disease can progress to ESRD although this outcome appears to be later in PH2 than in PH1, in which 50% of affected individuals have ESRD by age 25 years [Leumann & Hoppe 2001]. Once ESRD occurs, deposition of oxalate can occur in organs other than kidney, including bone, bone marrow, retina, and myocardium [Wichmann et al 2003, Wachter et al 2006].

Genotype-Phenotype Correlations The low prevalence of PH2 does not allow genotype-phenotype correlations at the present time.

Differential DiagnosisStone disease. For any individual presenting with symptoms related to renal stone disease it is essential to analyze the stone if at all possible as this can help to direct the clinician to a particular line of investigation. The stones in individuals with PH2 are calcium oxalate.Urine should be analyzed for a stone risk profile that typically includes assessment of urine oxalate, calcium, magnesium, citrate, phosphate, and urate. Individuals with PH2 typically have urine oxalate excretions greater than 0.7 mmol/1.73 m²/day, in excess of levels usually seen in idiopathic calcium oxalate nephrolithiasis.Other heritable disorders that present with early stone formation include PH1, PH3, Dent’s disease, renal tubular acidosis, cystinuria, xanthinuria, and 2,8 dihydroxyadeninuria.Secondary hyperoxaluria. Disorders of the gastrointestinal tract leading to malabsorption have the potential to increase oxalate absorption and lead to hyperoxaluria; they can usually be excluded based on history.In addition, diets high in oxalate (for a listing of oxalate content of foods, see Holmes & Kennedy [2000] and Marcason [2006]) and low in calcium should be excluded and measurement of urine oxalate repeated on an oxalate-restricted diet. Megadoses of vitamin C (4 g/day) have led to hyperoxaluria [Nasr et al 2006], as has (deliberate or accidental) ingestion of ethylene glycol. Primary hyperoxaluria type 1 (PH1) is caused by a deficiency of the liver peroxisomal enzyme alanine:glyoxylate aminotransferase (AGT), which catalyzes the conversion of glyoxylate to glycine. When AGT activity is absent, glyoxylate is converted to oxalate, which forms insoluble calcium salts that accumulate in the kidney and other organs. Individuals with PH1 are at risk for recurrent nephrolithiasis (deposition of calcium oxalate in the renal pelvis/urinary tract), nephrocalcinosis (deposition of calcium oxalate in the renal parenchyma), or ESRD with a history of renal stones or oxalosis [Danpure 2001]. Although the hyperoxaluria is present from birth and most individuals present in childhood or adolescence, age at symptom onset ranges from infancy to adulthood. Approximately 15% of affected individuals present before age four to six months with severe disease including nephrocalcinosis; 55% present in childhood or early adolescence with symptomatic nephrolithiasis; and the remainder present in adulthood with recurrent renal stones. Untreated PH1 often progresses to nephrolithiasis/nephrocalcinosis, decline in renal function, oxalosis (widespread tissue deposition of calcium oxalate), and death from ESRD. Diagnosis relies on: (1) either (a) detection of increased urinary oxalate excretion (or elevated oxalate:creatinine ratio) or (b) in the setting of moderate to advanced renal failure, increased plasma oxalate concentration; and (2) deficiency of AGT catalytic activity from liver biopsy or molecular genetic testing of AGXT, the only gene known to be associated with PH1. Inheritance is autosomal recessive.Primary hyperoxaluria type 3 (PH3) has recently been described [Belostotsky et al 2010] with a phenotype similar to that of PH1 and PH2. Diagnosis relies on the exclusion of PH1 and PH2 and sequence analysis of HOGA1. Mutations in HOGA1 result in deficiency of mitochondrial 4-hydroxy-2-oxoglutarate aldolase, an enzyme that catalyzes one of the steps in the metabolism of hydroxyproline. The hyperoxaluria in individuals with PH3 arises from breakdown of the substrate for the enzyme rather than excessive production of glyoxylate.End-stage renal disease (ESRD). For persons presenting in ESRD, reliable measurement of urine oxalate excretion is not possible. While plasma oxalate elevations ranging up to 40 μmol/L may be detected with any form of ESRD, plasma oxalate concentrations exceeding 50 μmol/L are suggestive of primary hyperoxaluria. While PH1 and PH2 are a rare cause of ESRD in adults, PH can account for 0.7%-1.6% of ESRD in children. In a native kidney or renal allograft biopsy, PH should be considered if birefringent crystals are seen under polarized light. Although the measurement of plasma L-glycerate can identify individuals with PH2 who are in ESRD, such testing is not routinely available. Definitive diagnosis requires analysis of relevant enzymes in a liver biopsy or molecular genetic testing. Note to clinicians: For a patient-specific ‘simultaneous consult’ related to this disorder, go to , an interactive diagnostic decision support software tool that provides differential diagnoses based on patient findings (registration or institutional access required).

ManagementEvaluations Following Initial Diagnosis To establish the extent of disease in an individual diagnosed with primary hyperoxaluria type 2 (PH2), the following evaluations are recommended [Leumann & Hoppe 2001]:Assessment of renal function If moderate to advanced ESRD is present, assessment of systemic oxalate deposition in tissue and bone: Bone X-rays to look for radiodense metaphyseal bands Ophthalmic examination of the retina to look for oxalate crystalsEvaluation of cardiac function by echocardiography Treatment of ManifestationsReduction of calcium oxalate supersaturation. As with PH1, conservative therapy is applied with the aim of minimizing oxalate-related renal injury and preserving renal function. Treatment of persons with preserved renal function, reviewed by Leumann & Hoppe [2001], essentially aims to improve oxalate solubility as follows:Adequate fluid intake (>2.5 L/m² surface area/day)Urinary inhibitors of calcium oxalate crystallization:Orthophosphate treatment (20-60 mg/kg body weight/day) [Leumann & Hoppe 2001] (20-60 mg/kg body weight/day) Potassium citrate (0.1-0.15 g/kg body weight/day) [Leumann & Hoppe 2001] Magnesium supplements (200-300 mg/day in divided doses) [Watts 1994] Dialysis. Because the plasma oxalate concentration begins to rise when the renal clearance is less than 40 mL/min/1.73 m², early initiation of dialysis or preemptive kidney-only transplantation is preferred. For patients in ESRD, intensive (daily) dialysis is required to maximize oxalate removal. As in PH1, the longer the individual with PH2 is on dialysis the more likely systemic oxalate deposition will occur. Organ transplantation. Kidney transplantation alone has been used in PH2 with varying success. Careful management in the postoperative period, with attention to brisk urine output and use of calcium oxalate urinary inhibitors, minimizes the risk of allograft loss as a result of oxalate deposition. To date, liver-kidney transplantation has not been used in PH2; however, as there is more enzyme present in the liver than in other tissues [Cregeen et al 2003], this strategy may have some merit. Other. Pharmacologic doses of pyridoxine are used as a treatment in PH1 because of its role as cofactor for the defective enzyme. Its role in PH2 is unproven, but doses in the range of that found in typical multivitamin tablets have been used in an attempt to boost transaminases (including alanine:glyoxylate aminotransferase) with glyoxylate metabolizing activity. Prevention of Primary ManifestationsThe main preventative treatment is to maintain adequate hydration status and to enhance calcium oxalate solubility with exogenous citrate and neutral phosphates as described in Treatment of Manifestations. SurveillanceFrequency of testing depends on the center; however, as a guide, the following are recommended:Quarterly. Assessment of renal function, blood pressure, and hematocritSix monthly to annually. Renal imaging (ultrasound or CT examination) to assess renal stone burden*Annually. Examination for involvement of the skin, bone, eye, or thyroid^* For pregnant women with PH2, close monitoring by both an obstetrician and nephrologist because of the increased risk of developing nephrolithiasis during pregnancy or after delivery *Investigations should likely occur more often in newly diagnosed symptomatic individuals or in children younger than age two to three years. Agents/Circumstances to AvoidThe following should be avoided:DehydrationExcessive ascorbate (i.e., vitamin C; >1000 mg/day) Foods rich in oxalate (chocolate, rhubarb, spinach, and starfruit in particular) Evaluation of Relatives at RiskIn order to delay disease onset in asymptomatic relatives, it is prudent to screen at-risk family members before symptoms occur by measuring urinary oxalate excretion or by molecular genetic testing if the disease-causing mutations in the family are known. Molecular genetic testing tends to be more reliable as urine oxalate output can be variable in childhood.See Genetic Counseling for issues related to testing of at-risk relatives for genetic counseling purposes.Therapies Under InvestigationTreatment with Oxalobacter formigenes is currently undergoing clinical trials in patients with hyperoxaluria and may provide an additional form of treatment for PH1 and PH2 [Hoppe et al 2006] by inducing oxalate excretion into the gut [Hatch & Freel 2003]. Search ClinicalTrials.gov for access to information on clinical studies for a wide range of diseases and conditions.

Molecular GeneticsInformation in the Molecular Genetics and OMIM tables may differ from that elsewhere in the GeneReview: tables may contain more recent information. —ED.Table A. Primary Hyperoxaluria Type 2: Genes and DatabasesView in own windowGene SymbolChromosomal LocusProtein NameLocus SpecificHGMDGRHPR9p13​.2Glyoxylate reductase/hydroxypyruvate reductaseGRHPR mutation database
GRHPR homepage - Mendelian genesGRHPRData are compiled from the following standard references: gene symbol from HGNC; chromosomal locus, locus name, critical region, complementation group from OMIM; protein name from UniProt. For a description of databases (Locus Specific, HGMD) to which links are provided, click here.Table B. OMIM Entries for Primary Hyperoxaluria Type 2 (View All in OMIM) View in own window 260000HYPEROXALURIA, PRIMARY, TYPE II; HP2 604296GLYOXYLATE REDUCTASE/HYDROXYPYRUVATE REDUCTASE; GRHPRNormal allelic variants. GRHPR (previously known as GLXR) is composed of nine exons spanning approximately 9 kb; the entire gene can be found within a single contig, NT_008413.17. The mRNA [Cramer et al 1999, Rumsby & Cregeen 1999] encodes a protein of 328 amino acids. Two polymorphic variants, a dinucleotide repeat in intron 8 (c.866-10_25(CT)n) and a single nucleotide variant c.579A>G in exon 6, have been described [Cregeen et al 2003]. Several others have now been identified. Information on specific allelic variants may be available in Table A and/or Pathologic allelic variants).Pathologic allelic variants. A number of mutations have been described in GRHPR [Cramer et al 1999, Webster et al 2000, Lam et al 2001, Cregeen et al 2003, Booth et al 2006, Takayama et al 2007]. PCR amplification of genomic DNA with sequencing of individual exons and intron-exon boundaries has identified a total of 24 mutations to date [Cramer et al 1999, Webster et al 2000, Cregeen et al 2003, Takayama et al 2007, Levin-Iaina et al 2009]. Information on specific allelic variants may also be available in Table A.Just over 50% of mutations in GRPHR are minor deletions; the remainder are point mutations affecting a splice site or leading to a missense change [Cramer et al 1999, Webster et al 2000, Cregeen et al 2003, Takayama et al 2007]. To date, c.103delG has been found primarily in whites and c.403_404+2delAAGT (formerly c.403_405+2delAAGT) in Asians.Tissue-specific differences in expression of mutations and polymorphisms has been reported; until this issue is understood, it is recommended that expression studies use only GRHPR cDNA derived from liver [Bhat et al 2005]. Table 2. Selected GRHPR Allelic Variants View in own windowClass of Variant AlleleDNA Nucleotide Change Protein Amino Acid Change Reference SequencesNormalc.579A>GNoneNM_012203​.1
NP_036335​.1
NT_008413​.18c.866-10_25(CT)nNonePathologicc.103delGp.Asp35Thrfs*11c.403_404+2delAAGTMissplicingSee Quick Reference for an explanation of nomenclature. GeneReviews follows the standard naming conventions of the Human Genome Variation Society (www​.hgvs.org). Normal gene product. The normal protein is a homodimer. The protein has a large coenzyme-binding domain (residues 107-298) and a smaller substrate-binding domain (5-106 and 299-328) [Booth et al 2006]. A prominent extended helical and loop region wraps around the other subunit (dimerization loop, residues 123-149). The apex of this loop contains a tryptophan residue at position 141 and the residue from one subunit is projected into the active site of the other subunit and contributes to substrate specificity [Booth et al 2006]. The protein is found primarily in the cytosol although some immunoreactivity has been found within the mitochondria of cells [Knight & Holmes 2005, Behnam et al 2006]. The significance of this finding in vivo is unknown.Abnormal gene product. All the missense mutations described to date result in proteins with no catalytic activity [Webster et al 2000, Cregeen et al 2003]. Other mutations that affect splicing or create frameshifts or nonsense mutations would also fail to yield a functional product. All mutations are, therefore, essentially null alleles.