Diagnosis and management of primary hyperoxalurias: best practices.

The primary hyperoxalurias (PH 1, 2, and 3) are rare autosomal recessive disorders of glyoxylate metabolism resulting in hepatic overproduction of oxalate. Clinical presentations that should prompt consideration of PH include kidney stones, nephrocalcinosis, and kidney failure of unknown etiology, especially with echogenic kidneys on ultrasound. PH1 is the most common and severe of the primary hyperoxalurias with a high incidence of kidney failure as early as infancy. Until the recent availability of a novel RNA interference (RNAi) agent, PH care was largely supportive of eventual need for kidney/liver transplantation in PH1 and PH2. Together with the Oxalosis and Hyperoxaluria Foundation, the authors developed a diagnostic algorithm for PH1 and in this report outline best clinical practices related to its early diagnosis, supportive treatment, and long-term management, including the use of the novel RNAi. PH1-focused approaches to dialysis and kidney/liver transplantation for PH patients with progression to chronic kidney disease/kidney failure and systemic oxalosis are suggested. Therapeutic advances for this devastating disease heighten the importance of early diagnosis and informed treatment.

Natural history of urine and plasma oxalate in children with primary hyperoxaluria type 1.

BACKGROUND: Primary hyperoxaluria type 1 (PH1) is a rare, severe genetic disease causing increased hepatic oxalate production resulting in urinary stone disease, nephrocalcinosis, and often progressive chronic kidney disease. Little is known about the natural history of urine and plasma oxalate values over time in children with PH1. METHODS: For this retrospective observational study, we analyzed data from genetically confirmed PH1 patients enrolled in the Rare Kidney Stone Consortium PH Registry between 2003 and 2018 who had at least 2 measurements before age 18 years of urine oxalate-to-creatinine ratio (Uox:cr), 24-h urine oxalate excretion normalized to body surface area (24-h Uox), or plasma oxalate concentration (Pox). We compared values among 3 groups: homozygous G170R, heterozygous G170R, and non-G170R AGXT variants both before and after initiating pyridoxine (B6). RESULTS: Of 403 patients with PH1 in the registry, 83 met the inclusion criteria. Uox:cr decreased rapidly over the first 5 years of life. Both before and after B6 initiation, patients with non-G170R had the highest Uox:cr, 24-h Uox, and Pox. Patients with heterozygous G170R had similar Uox:cr to homozygous G170R prior to B6. Patients with homozygous G170R had the lowest 24-h Uox and Uox:cr after B6. Urinary oxalate excretion and Pox tend to decrease over time during childhood. eGFR over time was not different among groups. CONCLUSIONS: Children with PH1 under 5 years old have relatively higher urinary oxalate excretion which may put them at greater risk for nephrocalcinosis and kidney failure than older PH1 patients. Those with homozygous G170R variants may have milder disease. A higher resolution version of the Graphical abstract is available as Supplementary information.

Characterization of Stone Events in Patients With Type 3 Primary Hyperoxaluria.

PURPOSE: Hallmarks of primary hyperoxaluria type 3 are nephrolithiasis and hyperoxaluria. However, little is known about factors influencing stone formation in this disease. We characterized stone events and examined associations with urine parameters and kidney function in a primary hyperoxaluria type 3 population. MATERIALS AND METHODS: We retrospectively analyzed clinical, and laboratory data of 70 primary hyperoxaluria type 3 patients enrolled in the Rare Kidney Stone Consortium Primary Hyperoxaluria Registry. RESULTS: Kidney stones occurred in 65/70 primary hyperoxaluria type 3 patients (93%). Among the 49 patients with imaging available, the median (IQR) number of stones was 4 (2, 5), with largest stone 7 mm (4, 10) at first imaging. Clinical stone events occurred in 62/70 (89%) with median number of events per patient 3 (2, 6; range 1-49). Age at first stone event was 3 years (0.99, 8.7). Lifetime stone event rate was 0.19 events/year (0.12, 0.38) during follow-up of 10.7 (4.2, 26.3) years. Among 326 total clinical stone events, 139 (42.6%) required surgical intervention. High stone event rates persisted for most patients through the sixth decade of life. Analysis was available for 55 stones: pure calcium oxalate accounted for 69%, with mixed calcium oxalate and phosphate in 22%. Higher calcium oxalate supersaturation was associated with increased lifetime stone event rate after adjusting for age at first event (IRR [95%CI] 1.23 [1.16, 1.32]; P < .001). By the fourth decade, estimated glomerular filtration rate was lower in primary hyperoxaluria type 3 patients than the general population. CONCLUSIONS: Stones impose a lifelong burden on primary hyperoxaluria type 3 patients. Reducing urinary calcium oxalate supersaturation may reduce event frequency and surgical intervention.

Posttransplant recurrence of calcium oxalate crystals in patients with primary hyperoxaluria: Incidence, risk factors, and effect on renal allograft function.

Primary hyperoxaluria (PH) is a metabolic defect that results in oxalate overproduction by the liver and leads to kidney failure due to oxalate nephropathy. As oxalate tissue stores are mobilized after transplantation, the transplanted kidney is at risk of recurrent disease. We evaluated surveillance kidney transplant biopsies for recurrent calcium oxalate (CaOx) deposits in 37 kidney transplants (29 simultaneous kidney and liver [K/L] transplants and eight kidney alone [K]) in 36 PH patients and 62 comparison transplants. Median follow-up posttransplant was 9.2 years (IQR: [5.3, 15.1]). The recurrence of CaOx crystals in surveillance biopsies in PH at any time posttransplant was 46% overall (41% in K/L, 62% in K). Higher CaOx crystal index (which accounted for biopsy sample size) was associated with higher plasma and urine oxalate following transplant (p < .01 and p < .02, respectively). There was a trend toward higher graft failure among PH patients with CaOx crystals on surveillance biopsies compared with those without (HR 4.43 [0.88, 22.35], p = .07). CaOx crystal deposition is frequent in kidney transplants in PH patients. The avoidance of high plasma oxalate and reduction of CaOx crystallization may decrease the risk of recurrent oxalate nephropathy following kidney transplantation in patients with PH. This study was approved by the IRB at Mayo Clinic.

Estimated GFR Slope Across CKD Stages in Primary Hyperoxaluria Type 1.

RATIONALE & OBJECTIVE: Primary hyperoxaluria type 1 (PH1) is an autosomal recessive disorder of glyoxylate metabolism that results in early-onset kidney stone disease, nephrocalcinosis, and kidney failure. There is an unmet need for reliable markers of disease progression to test effectiveness of new treatments for patients with PH. In this study, we assessed the rate of estimated glomerular filtration rate (eGFR) decline across chronic kidney disease (CKD) glomerular filtration rate (GFR) categories (CKD G2-G5) in a cohort of patients with PH1. STUDY DESIGN: Retrospective observational study. SETTING & PARTICIPANTS: Patients with PH1 enrolled in the Rare Kidney Stone Consortium (RKSC) registry who did not have kidney failure at diagnosis and who had at least 2 eGFR values recorded from within 1 month of diagnosis until their last contact date or incident kidney failure event. PREDICTORS: CKD GFR category, baseline patient and laboratory characteristics. OUTCOME: Annualized rate of eGFR decline. ANALYTICAL APPROACH: Generalized estimating equations and linear regression were used to evaluate the associations between CKD GFR category, baseline patient and laboratory characteristics, and annual change in eGFR during follow-up. RESULTS: Compared with the slope in CKD G2 (-2.3 mL/min/1.73 m2 per year), the mean annual eGFR decline was nominally steeper in CKD G3a (-5.3 mL/min/1.73 m2 per year) and statistically significantly more rapid in CKD G3b and G4 (-14.7 and -16.6 mL/min/1.73 m2 per year, respectively). In CKD G2, older age was associated with a more rapid rate of eGFR decline (P = 0.01). A common PH1-causing variant of alanine glyoxylate aminotransferase, a glycine to arginine substitution at amino acid 170 (G170R), appeared to be associated with less severe annual decline in eGFR. LIMITATIONS: Data at regular time points were not available for all patients due to reliance on voluntary reporting in a retrospective rare disease registry. CONCLUSIONS: The eGFR decline was not uniform across CKD GFR categories in this PH1 population, with a higher rate of eGFR decline in CKD G3b and G4. Thus, CKD GFR category needs to be accounted for when analyzing eGFR change in the setting of PH1.

Primary Hyperoxaluria Type 3 Can Also Result in Kidney Failure: A Case Report.

Primary hyperoxaluria (PH) is a group of genetic disorders that result in an increased hepatic production of oxalate. PH type 3 (PH3) is the most recently identified subtype and results from mutations in the mitochondrial 4-hydroxy-2-oxoglutarate aldolase gene (HOGA1). To date, there have been 2 cases of kidney failure reported in PH3 patients. We present a case of a young man with a history of recurrent urinary tract infections and voiding dysfunction who developed kidney failure at 33 years of age. He developed a bladder stone and bilateral staghorn calculi at 12 years of age. Initial metabolic evaluation revealed hyperoxaluria with very low urinary citrate excretion on multiple measurements for which he was placed on oral citrate supplements. Further investigation of the hyperoxaluria was not completed as the patient was lost to follow-up observation until he presented at 29 years of age with chronic kidney disease stage 4 (estimated glomerular filtration rate 24mL/min/1.73m2). Hemodialysis 3 times a week was started at 33 years of age, and subsequent genetic testing revealed a homozygous HOGA1 mutation (C.973G>A p.Gly325Ser) diagnostic of PH3. The patient is currently being evaluated for all treatment options including possible liver/kidney transplantation. All cases of a childhood history of recurrent urinary stone disease with marked hyperoxaluria should prompt genetic testing for the 3 known PH types. Hyperhydration and crystallization inhibitors (citrate) are standard of care, but the role of RNA interference agents for all 3 forms of PH is also under active study.

Clinical characterization of primary hyperoxaluria type 3 in comparison with types 1 and 2.

BACKGROUND: Primary hyperoxaluria (PH) type 3 (PH3) is caused by mutations in the hydroxy-oxo-glutarate aldolase 1 gene. PH3 patients often present with recurrent urinary stone disease in the first decade of life, but prior reports suggested PH3 may have a milder phenotype in adults. This study characterized clinical manifestations of PH3 across the decades of life in comparison with PH1 and PH2. METHODS: Clinical information was obtained from the Rare Kidney Stone Consortium PH Registry (PH1, n = 384; PH2, n = 51; PH3, n = 62). RESULTS: PH3 patients presented with symptoms at a median of 2.7 years old compared with PH1 (4.9 years) and PH2 (5.7 years) (P = 0.14). Nephrocalcinosis was present at diagnosis in 4 (7%) PH3 patients, while 55 (89%) had stones. Median urine oxalate excretion was lowest in PH3 patients compared with PH1 and PH2 (1.1 versus 1.6 and 1.5 mmol/day/1.73 m2, respectively, P < 0.001) while urine calcium was highest in PH3 (112 versus 51 and 98 mg/day/1.73 m2 in PH1 and PH2, respectively, P < 0.001). Stone events per decade of life were similar across the age span and the three PH types. At 40 years of age, 97% of PH3 patients had not progressed to end-stage kidney disease compared with 36% PH1 and 66% PH2 patients. CONCLUSIONS: Patients with all forms of PH experience lifelong stone events, often beginning in childhood. Kidney failure is common in PH1 but rare in PH3. Longer-term follow-up of larger cohorts will be important for a more complete understanding of the PH3 phenotype.

Recovery From Dialysis in Patients With Primary Hyperoxaluria Type 1 Treated With Pyridoxine: A Report of 3 Cases.

Primary hyperoxaluria type 1 (PH1) is a genetic disorder characterized by overproduction of oxalate and eventual kidney failure. Kidney failure is usually irreversible in PH1. However, in patients with PH1 homozygous for the G170R mutation (in which the glycine at amino acid 170 is replaced by an arginine), pyridoxine is an enzyme cofactor and decreases urinary oxalate excretion by reducing hepatic oxalate production. We report recovery from dialysis in 3 patients with PH1 homozygous for the G170R mutation in response to pharmacologic-dose pyridoxine treatment. Median age at initiation or resumption of pyridoxine treatment was 37 (range, 20-53) years, and median daily pyridoxine dose was 8.8 (range, 6.8-14.0) mg per kilogram of body weight. Duration of hemodialysis before recovery of kidney function was 10 (range, 5-19) months. Plasma oxalate concentration improved after recovery of kidney function. At a median of 3 (range, 2-46) months following discontinuation of hemodialysis, estimated glomerular filtration rate was 34 (range, 23-52) mL/min/1.73m2, plasma oxalate concentration was 8.8 (range, 4.6-11.3) µmol/L, and urinary oxalate excretion was 0.93 (range, 0.47-1.03) mmol/d. Kidney function was maintained during a median of 3.2 (range, 1.3-3.8) years of follow-up. These observations suggest that kidney failure may be reversible in a subset of patients with PH1 homozygous for the G170R mutation treated with pharmacologic-dose pyridoxine.

Plasma oxalate and eGFR are correlated in primary hyperoxaluria patients with maintained kidney function-data from three placebo-controlled studies.

BACKGROUND: In patients with primary hyperoxaluria (PH), endogenous oxalate overproduction increases urinary oxalate excretion, leading to compromised kidney function and often kidney failure. Highly elevated plasma oxalate (Pox) is associated with systemic oxalate deposition in patients with PH and severe chronic kidney disease (CKD). The relationship between Pox and estimated glomerular filtration rate (eGFR) in patients with preserved kidney function, however, is not well established. Our analysis aimed to investigate a potential correlation between these parameters in PH patients from three randomized, placebo-controlled trials (studies OC3-DB-01, OC3-DB-02, and OC5-DB-01). METHODS: Baseline data from patients with a PH diagnosis (type 1, 2, or 3) and eGFR > 40 mL/min/1.73 m2 were analyzed for a correlation between eGFR and Pox using Spearman's rank and Pearson's correlation coefficients. Data were analyzed by individual study and additionally were pooled for Studies OC3-DB-02 and OC5-DB-01 in which the same Pox assay was used. RESULTS: A total of 106 patients were analyzed. A statistically significant inverse Spearman's correlation between eGFR and Pox was observed across all analyses; correlation coefficients were - 0.44 in study OC3-DB-01, - 0.55 in study OC3-DB-02, - 0.51 in study OC5-DB-01, and - 0.49 in the pooled studies (p < 0.0064). CONCLUSIONS: Baseline evaluations showed a moderate and statistically significant inverse correlation between eGFR and Pox in patients with PH already at early stages of CKD (stages 1-3b), demonstrating that a correlation is present before substantial loss in kidney function occurs.

Clinical features of genetically confirmed patients with primary hyperoxaluria identified by clinical indication versus familial screening.

Primary hyperoxaluria is a rare monogenic disorder characterized by excessive hepatic production of oxalate leading to recurrent nephrolithiasis, nephrocalcinosis, and progressive kidney damage. Most patients with primary hyperoxaluria are diagnosed after clinical suspicion based on symptoms. Since some patients are detected by family screening following detection of an affected family member, we compared the clinical phenotype of these two groups. Patients with primary hyperoxaluria types 1, 2, and 3 enrolled in the Rare Kidney Stone Consortium Primary Hyperoxaluria Registry were retrospectively analyzed following capture of clinical and laboratory results in the Registry. Among 495 patients with primary hyperoxaluria, 47 were detected by family screening. After excluding 150 patients with end stage kidney disease at diagnosis, 300 clinical suspicion and 45 family screening individuals remained. Compared to patients with clinical suspicion, those identified by family screening had significantly fewer stones at diagnosis (mean 1.2 vs. 3.6), although initial symptoms occurred at a similar age (median age 6.1 vs. 7.6 years). Urinary oxalate did not differ between these groups. The estimated glomerular filtration rate at diagnosis and its decline over time were similar for the two groups. Altogether, five of 45 in family screening and 67 of 300 of clinical suspicion individuals developed end stage kidney disease at last follow-up. Thus, patients with primary hyperoxaluria identified through family screening have significant disease despite no outward clinical suspicion at diagnosis. Since promising novel treatments are emerging, genetic screening of family members is warranted because they are at significant risk for disease progression.

Prevalence of low molecular weight proteinuria and Dent disease 1 CLCN5 mutations in proteinuric cohorts.

BACKGROUND: Dent disease type 1 (DD1) is a rare X-linked disorder caused mainly by CLCN5 mutations. Patients may present with nephrotic-range proteinuria leading to erroneous diagnosis of focal segmental glomerulosclerosis (FSGS) and unnecessary immunosuppressive treatments. METHODS: The following cohorts were screened for CLCN5 mutations: Chronic Kidney Disease in Children (CKiD; n = 112); Multicenter FSGS-Clinical Trial (FSGS-CT) (n = 96), and Novel Therapies for Resistant FSGS Trial (FONT) (n = 30). Urinary α1-microglobulin (α1M), albumin (A), total protein (TP), and creatinine (Cr) were assessed from CKiD subjects (n = 104); DD1 patients (n = 14); and DD1 carriers (DC; n = 8). TP/Cr, α1M/Cr, α1M/TP, and A/TP from the CKiD cohort were compared with DD1 and DC. RESULTS: No CLCN5 mutations were detected. TP/Cr was lower in DC and CKiD with tubulointerstitial disease than in DD1 and CKiD with glomerular disease (p < 0.002). α1M/Cr was higher in DD1 than in CKiD and DC (p < 0.001). A/TP was lower in DD1, DC, and CKiD with tubulointerstitial disease and higher in CKiD with glomerular disease (p < 0.001). Thresholds for A/TP of ≤ 0.21 and α1M/Cr of ≥ 120 mg/g (> 13.6 mg/mmol) creatinine were good screens for Dent disease. CONCLUSIONS: CLCN5 mutations were not seen in screened CKiD/FSGS cohorts. In our study, a cutoff of TP/Cr > 600 mg/g (> 68 mg/mmol) and A/TP of < 0.3 had a high sensitivity and specificity to distinguish DD1 from both CKiD glomerular and tubulointerstitial cohorts. α1M/Cr ≥ 120 mg/g (> 13.6 mg/mmol) had the highest sensitivity and specificity when differentiating DD1 and studied CKiD populations.

Plasma Oxalate as a Predictor of Kidney Function Decline in a Primary Hyperoxaluria Cohort.

This retrospective analysis investigated plasma oxalate (POx) as a potential predictor of end-stage kidney disease (ESKD) among primary hyperoxaluria (PH) patients. PH patients with type 1, 2, and 3, age 2 or older, were identified in the Rare Kidney Stone Consortium (RKSC) PH Registry. Since POx increased with falling estimated glomerular filtration rate (eGFR), patients were stratified by chronic kidney disease (CKD) subgroups (stages 1, 2, 3a, and 3b). POx values were categorized into quartiles for analysis. Hazard ratios (HRs) and 95% confidence intervals (95% CIs) for risk of ESKD were estimated using the Cox proportional hazards model with a time-dependent covariate. There were 118 patients in the CKD1 group (nine ESKD events during follow-up), 135 in the CKD 2 (29 events), 72 in CKD3a (34 events), and 45 patients in CKD 3b (31 events). During follow-up, POx Q4 was a significant predictor of ESKD compared to Q1 across CKD2 (HR 14.2, 95% CI 1.8-115), 3a (HR 13.7, 95% CI 3.0-62), and 3b stages (HR 5.2, 95% CI 1.1-25), p < 0.05 for all. Within each POx quartile, the ESKD rate was higher in Q4 compared to Q1-Q3. In conclusion, among patients with PH, higher POx concentration was a risk factor for ESKD, particularly in advanced CKD stages.

Oxalosis Associated With High-Dose Vitamin C Ingestion in a Peritoneal Dialysis Patient.

We report a case of systemic oxalosis involving the eyes and joints due to long-term use of high-dose vitamin C in a patient receiving maintenance peritoneal dialysis (PD). This 76-year-old woman with autosomal dominant polycystic kidney disease underwent living unrelated kidney transplantation 10 years earlier. The transplant failed 6 months before presentation, and she initiated hemodialysis therapy before transitioning to PD therapy 4 months later. During the month before presentation, the patient noted worsening arthralgias and decreased vision. Ophthalmologic examination revealed proliferative retinopathy and calcium oxalate crystals. Plasma oxalate level was markedly elevated at 187 (reference range, <1.7) µmol/L, and urine oxalate-creatinine ratio was high (0.18mg/mg). The patient reported taking up to 4g of vitamin C per day for several years. Workup for causes of primary and secondary hyperoxaluria was otherwise negative. Vitamin C use was discontinued, and the patient transitioned to daily hemodialysis for 2 weeks. Plasma oxalate level before the dialysis session decreased but remained higher (30-53µmol/L) than typical for dialysis patients. Upon discharge, the patient remained on thrice-weekly hemodialysis therapy with stabilized vision and improved joint symptoms. This case highlights the risk of high-dose vitamin C use in patients with advanced chronic kidney disease, especially when maintained on PD therapy.

Hydroxyproline Metabolism and Oxalate Synthesis in Primary Hyperoxaluria.

Background Endogenous oxalate synthesis contributes to calcium oxalate stone disease and is markedly increased in the inherited primary hyperoxaluria (PH) disorders. The incomplete knowledge regarding oxalate synthesis complicates discovery of new treatments. Hydroxyproline (Hyp) metabolism results in the formation of oxalate and glycolate. However, the relative contribution of Hyp metabolism to endogenous oxalate and glycolate synthesis is not known.Methods To define this contribution, we performed primed, continuous, intravenous infusions of the stable isotope [15N,13C5]-Hyp in nine healthy subjects and 19 individuals with PH and quantified the levels of urinary 13C2-oxalate and 13C2-glycolate formed using ion chromatography coupled to mass detection.Results The total urinary oxalate-to-creatinine ratio during the infusion was 73.1, 70.8, 47.0, and 10.6 mg oxalate/g creatinine in subjects with PH1, PH2, and PH3 and controls, respectively. Hyp metabolism accounted for 12.8, 32.9, and 14.8 mg oxalate/g creatinine in subjects with PH1, PH2, and PH3, respectively, compared with 1.6 mg oxalate/g creatinine in controls. The contribution of Hyp to urinary oxalate was 15% in controls and 18%, 47%, and 33% in subjects with PH1, PH2, and PH3, respectively. The contribution of Hyp to urinary glycolate was 57% in controls, 30% in subjects with PH1, and <13% in subjects with PH2 or PH3.Conclusions Hyp metabolism differs among PH types and is a major source of oxalate synthesis in individuals with PH2 and PH3. In patients with PH1, who have the highest urinary excretion of oxalate, the major sources of oxalate remain to be identified.

Silent Tyrosinemia Type I Without Elevated Tyrosine or Succinylacetone Associated with Liver Cirrhosis and Hepatocellular Carcinoma.

Tyrosinemia type I (TYRSN1, TYR I) is caused by fumarylacetoacetate hydrolase (FAH) deficiency and affects approximately one in 100,000 individuals worldwide. Pathogenic variants in FAH cause TYRSN1, which induces cirrhosis and can progress to hepatocellular carcinoma (HCC). TYRSN1 is characterized by the production of a pathognomonic metabolite, succinylacetone (SUAC) and is included in the Recommended Uniform Screening Panel for newborns. Treatment intervention is effective if initiated within the first month of life. Here, we describe a family with three affected children who developed HCC secondary to idiopathic hepatosplenomegaly and cirrhosis during infancy. Whole exome sequencing revealed a novel homozygous missense variant in FAH (Chr15(GRCh38):g.80162305A>G; NM_000137.2:c.424A > G; NP_000128.1:p.R142G). This novel variant involves the catalytic pocket of the enzyme, but does not result in increased SUAC or tyrosine, making the diagnosis of TYRSN1 problematic. Testing this novel variant using a rapid, in vivo somatic mouse model showed that this variant could not rescue FAH deficiency. In this case of atypical TYRSN1, we show how reliance on SUAC as a primary diagnostic test can be misleading in some patients with this disease. Augmentation of current screening for TYRSN1 with targeted sequencing of FAH is warranted in cases suggestive of the disorder.

Assessment of Urine Proteomics in Type 1 Primary Hyperoxaluria.

BACKGROUND: Primary hyperoxaluria type 1 (PH1) and idiopathic hypercalciuria (IHC) are stone-forming diseases that may result in the formation of calcium (Ca) oxalate (Ox) stones, nephrocalcinosis, and progressive chronic kidney disease (CKD). Poorer clinical outcome in PH1 is segregated by the highest urine (Ur)-Ox (UrOx), while IHC outcomes are not predictable by UrCa. We hypothesized that differences would be found in selected Ur-protein (PRO) patterns in PH1 and IHC, compared to healthy intra-familial sibling controls (C) of PH1 patients. We also hypothesized that the PRO patterns associated with higher UrOx levels would reflect injury, inflammation, biomineralization, and abnormal tissue repair processes in PH1. METHODS: Twenty four-hour Ur samples were obtained from 3 cohorts: PH1 (n = 47); IHC (n = 35) and C (n = 13) and were analyzed using targeted platform-based multi-analyte profile immunoassays and for UrOx and UrCa by biochemical measurements. RESULTS: Known stone matrix constituents, osteopontin, calbindin, and vitronectin were lowest in PH1 (C > IHC > PH1; p < 0.05). Ur-interleukin-10; chromogranin A; epidermal growth factor (EGF); insulin-like growth factor-1 (IGF-1), and macrophage inflammatory PRO-1α (MIP-1α) were higher in PH1 > C (p = 0.03 to p < 0.05). Fetuin A; IGF-1, MIP-1α, and vascular cell adhesion molecule-1 were highest in PH1 > IHC (p < 0.001 to p = 0.005). CONCLUSION: PH1 Ur-PROs reflected overt inflammation, chemotaxis, oxidative stress, growth factors (including EGF), and pro-angiogenic and calcification regulation/inhibition compared to the C and IHC cohorts. Many of the up- and downregulated PH1-PROs found in this study are also found in CKD, acute kidney injury, stone formers, and/or stone matrices. Further data analyses may provide evidence for PH1 unique PROs or demonstrate a poorer clinical outcome.

Phenotype-Genotype Correlations and Estimated Carrier Frequencies of Primary Hyperoxaluria.

Primary hyperoxaluria (PH) is a rare autosomal recessive disease characterized by oxalate accumulation in the kidneys and other organs. Three loci have been identified: AGXT (PH1), GRHPR (PH2), and HOGA1 (PH3). Here, we compared genotype to phenotype in 355 patients in the Rare Kidney Stone Consortium PH registry and calculated prevalence using publicly available whole-exome data. PH1 (68.4% of families) was the most severe PH type, whereas PH3 (11.0% of families) showed the slowest decline in renal function but the earliest symptoms. A group of patients with disease progression similar to that of PH3, but for whom no mutation was detected (11.3% of families), suggested further genetic heterogeneity. We confirmed that the AGXT p.G170R mistargeting allele resulted in a milder PH1 phenotype; however, other potential AGXT mistargeting alleles caused more severe (fully penetrant) disease. We identified the first PH3 patient with ESRD; a homozygote for two linked, novel missense mutations. Population analysis suggested that PH is an order of magnitude more common than determined from clinical cohorts (prevalence, approximately 1:58,000; carrier frequency, approximately 1:70). We estimated PH to be approximately three times less prevalent among African Americans than among European Americans because of a limited number of common European origin alleles. PH3 was predicted to be as prevalent as PH1 and twice as common as PH2, indicating that PH3 (and PH2) cases are underdiagnosed and/or incompletely penetrant. These results highlight a role for molecular analyses in PH diagnostics and prognostics and suggest that wider analysis of the idiopathic stone-forming population may be beneficial.

Nephrocalcinosis is a risk factor for kidney failure in primary hyperoxaluria.

Stone formation and nephrocalcinosis are both very common features of primary hyperoxaluria, yet the extent of each disease varies markedly between patients. Here we studied whether kidney damage from nephrocalcinosis and/or stone related events contributed to end-stage kidney disease (ESKD). Clinical information was analyzed from 348 patients enrolled in the Rare Kidney Stone Consortium Primary Hyperoxaluria registry and included demographic, laboratory and imaging features. Among all patients there were 277 with type 1, 37 with type 2, and 34 with type 3 primary hyperoxaluria. Overall, 58% passed a stone (mean 0.3/year) and one or more urologic procedures were required by 70% of patients (mean 0.15/year). Nephrocalcinosis was found in 34% of patients, including 41% with type 1 primary hyperoxaluria. High urine oxalate was associated with increased risk for both nephrocalcinosis and stone number, while low urine citrate was a risk factor for stone events and stone number. After adjustment for the type of primary hyperoxaluria, diagnosis by family screening and age at first image, the overall adjusted hazard ratio for ESKD among those with a history of nephrocalcinosis was 1.7 [95% CI 1.0-3.0], while the risk was 4.0 [1.9-8.5] for new onset nephrocalcinosis during follow-up. In contrast, the number of stones and stone events were not significantly associated with ESKD risk. Thus, nephrolithiasis and nephrocalcinosis appear to be pathophysiologically distinct entities. The presence of nephrocalcinosis implies increased risk for ESKD.