Systematic assessment of urinary hydroxy-oxo-glutarate for diagnosis and follow-up of primary hyperoxaluria type III

Effective Newborn Screening for Type 1 and 3 Primary Hyperoxaluria

Introduction

Newborn screening (NBS) programs for a defined set of eligible diseases have been enormously successful, but genomic NBS allowing for detection of additional treatable disorders has not been broadly implemented. All 3 types of primary hyperoxaluria (PH1-3) are rare autosomal recessive diseases caused by distinct defects of glyoxylate metabolism that are diagnosed genetically with certainty. Early diagnosis and treatment are mandatory to avoid renal failure or sequalae associated with persistent hyperoxaluria.

Methods

This prospective pilot study was undertaken within the framework of the German NBS. DNA samples extracted from dried blood spot cards were screened by multiplex polymerase chain reaction (PCR) for the 2 most prevalent variants: AGXT c.508G>A (PH1) and HOGA1 c.700 + 5G>T (PH3). Heterozygous AGXT/HOGA1 carriers received repeated spot urine analyses and, in case of persistent hyperoxaluria, complete Sanger sequencing of AGXT and HOGA1 genes, respectively.

Results

Between March 15, 2022 and June 30, 2023, additional screening for PH1 and PH3 was performed in 77,199 out of 222,638 newborns included in the regular NBS program. No homozygous individuals, but 274 potential carriers for the AGXT mistargeting and 287 potential carriers for the HOGA1 splice variant were identified. Further workup revealed 2 already symptomatic compound heterozygous infants, 1 with PH1 (genotype c.508G>A; c.33delC) and 1 with PH3 (genotype: c.700 + 5G>T; c.134C>G). A second symptomatic patient with PH1 (father of an identified carrier; genotype: c.508G>A; c.508G>A) was uncovered via family history.

Conclusion

This pilot study demonstrates the efficacy of a genomic neonatal screening program for PH even in relatively small cohorts.

A molecular journey on the pathogenesis of primary hyperoxaluria

PURPOSE OF REVIEW

Primary hyperoxalurias (PHs) are rare disorders caused by the deficit of liver enzymes involved in glyoxylate metabolism. Their main hallmark is the increased excretion of oxalate leading to the deposition of calcium oxalate stones in the urinary tract. This review describes the molecular aspects of PHs and their relevance for the clinical management of patients.

RECENT FINDINGS

Recently, the study of PHs pathogenesis has received great attention. The development of novel in vitro and in vivo models has allowed to elucidate how inherited mutations lead to enzyme deficit, as well as to confirm the pathogenicity of newly-identified mutations. In addition, a better knowledge of the metabolic consequences in disorders of liver glyoxylate detoxification has been crucial to identify the key players in liver oxalate production, thus leading to the identification and validation of new drug targets.

SUMMARY

The research on PHs at basic, translational and clinical level has improved our knowledge on the critical factors that modulate disease severity and the response to the available treatments, leading to the development of new drugs, either in preclinical stage or, very recently, approved for patient treatment.

Multicenter Long-Term Real World Data on Treatment With Lumasiran in Patients With Primary Hyperoxaluria Type 1

Introduction

The RNA interference (RNAi) medication lumasiran reduces hepatic oxalate production in primary hyperoxaluria type 1 (PH1). Data outside clinical trials are scarce.

Methods

We report on retrospectively and observationally obtained data in 33 patients with PH1 (20 with preserved kidney function, 13 on dialysis) treated with lumasiran for a median of 18 months.

Results

Among those with preserved kidney function, mean urine oxalate (Uox) decreased from 1.88 (baseline) to 0.73 mmol/1.73 m2 per 24h after 3 months, to 0.72 at 12 months, and to 0.65 at 18 months, but differed according to vitamin B6 (VB6) medication. The highest response was at month 4 (0.55, -70.8%). Plasma oxalate (Pox) remained stable over time. Glomerular filtration rate increased significantly by 10.5% at month 18. Nephrolithiasis continued active in 6 patients, nephrocalcinosis ameliorated or progressed in 1 patient each. At last follow-up, Uox remained above 1.5 upper limit of normal (>0.75 mmol/1.73 m2 per 24h) in 6 patients. Urinary glycolate (Uglyc) and plasma glycolate (Pglyc) significantly increased in all, urine citrate decreased, and alkali medication needed adaptation. Among those on dialysis, mean Pox and Pglyc significantly decreased and increased, respectively after monthly dosing (Pox: 78-37.2, Pglyc: 216.4-337.4 μmol/l). At quarterly dosing, neither Pox nor Pglyc were significantly different from baseline levels. An acid state was buffered by an increased dialysis regimen. Systemic oxalosis remained unchanged.

Conclusion

Lumasiran treatment is safe and efficient. Dosage (interval) adjustment necessities need clarification. In dialysis, lack of Pox reduction may relate to dissolving systemic oxalate deposits. Pglyc increment may be a considerable acid load requiring careful consideration, which definitively needs further investigation.

Genotype and Phenotype Characteristics of Chinese Pediatric Patients with Primary Hyperoxaluria

Primary hyperoxaluria (PH) is a rare monogenic disorder characterized by recurrent kidney stones, nephrocalcinosis, and renal impairment. To study the genotype and phenotype characteristics, we evaluated the clinical data of 42 Chinese pediatric PH patients who were diagnosed from May 2016 to April 2022. We found that patients with the PH3 type showed an earlier age of onset than those with the PH1 and PH2 types (1 versus 5 and 8 years, respectively, P < 0.001). Urine citrate was significantly lower in PH1 and PH2 patients than that in PH3 patients (91.81 and 85.56 versus 163.9 μg/mg, respectively, P = 0.044). Spot urine oxalate levels were slightly higher in PH1 than that in PH2 and PH3 patients (457.9 versus 182.38 and 309.14 μg/mg, respectively, P = 0.189). A significant negative correlation between the urine calcium/creatinine ratio and the oxalate/creatinine ratio was observed in the entire PH cohort (r = -0.360, P = 0.04) and the PH3 cohort (r = -0.674, P = 0.003). PH-causative genes showed hotspot mutations or regions, including c.815_816insGA and c.33dup in AGXT, 864_865del in GRHPR, and exon 6 skipping and c.769T>G in HOGA1. In the PH1 cohort, the estimated glomerular filtration rate (eGFR) was lowest in patients with heterozygous c.33dup. In the PH3 cohort, patients with heterozygous exon 6 skipping presented the lowest eGFR and a significant decrease in the renal survival advantage. In summary, PH1 patients exhibit much more severe phenotypes than those with other types. Hotspot mutations or regions exist in patients with all types of PH and show differences among ethnicities. Genotype-phenotype correlations are observed in PH1 and PH3.

The real world experience of pediatric primary hyperoxaluria patients in the PEDSnet clinical research network

The rarity of primary hyperoxaluria (PH) challenges our understanding of the disease. The purpose of our study was to describe the course of clinical care in a United States cohort of PH pediatric patients, highlighting health service utilization. We performed a retrospective cohort study of PH patients < 18 years old in the PEDSnet clinical research network from 2009 to 2021. Outcomes queried included diagnostic imaging and testing related to known organ involvement of PH, surgical and medical interventions specific to PH-related renal disease, and select PH-related hospital service utilization. Outcomes were evaluated relative to cohort entrance date (CED), defined as date of first PH-related diagnostic code. Thirty-three patients were identified: 23 with PH type 1; 4 with PH type 2; 6 with PH type 3. Median age at CED was 5.0 years (IQR 1.4, 9.3 years) with the majority being non-Hispanic white (73%) males (70%). Median follow-up between CED and most recent encounter was 5.1 years (IQR 1.2, 6.8). Nephrology and Urology were the most common specialties involved in care, with low utilization of other sub-specialties (12%-36%). Most patients (82%) had diagnostic imaging used to evaluate kidney stones; 11 (33%) had studies of extra-renal involvement. Stone surgery was performed in 15 (46%) patients. Four patients (12%) required dialysis, begun in all prior to CED; four patients required renal or renal/liver transplant.    Conclusion: In this large cohort of U.S. PH children, patients required heavy health care utilization with room for improvement in involving multi-disciplinary specialists. What is Known: • Primary hyperoxaluria (PH) is rare with significant implications on patient health. Typical involvement includes the kidneys; however, extra-renal manifestations occur. • Most large population studies describe clinical manifestations and involve registries. What is New: • We report the clinical journey, particularly related to diagnostic studies, interventions, multispecialty involvement, and hospital utilization, of a large cohort of PH pediatric patients in the PEDSnet clinical research network. • There are missed opportunities, particularly in that of specialty care, that could help in the diagnosis, treatment, and even prevention of known clinical manifestations.

Clinical practice recommendations for primary hyperoxaluria: an expert consensus statement from ERKNet and OxalEurope

Primary hyperoxaluria (PH) is an inherited disorder that results from the overproduction of endogenous oxalate, leading to recurrent kidney stones, nephrocalcinosis and eventually kidney failure; the subsequent storage of oxalate can cause life-threatening systemic disease. Diagnosis of PH is often delayed or missed owing to its rarity, variable clinical expression and other diagnostic challenges. Management of patients with PH and kidney failure is also extremely challenging. However, in the past few years, several new developments, including new outcome data from patients with infantile oxalosis, from transplanted patients with type 1 PH (PH1) and from patients with the rarer PH types 2 and 3, have emerged. In addition, two promising therapies based on RNA interference have been introduced. These developments warrant an update of existing guidelines on PH, based on new evidence and on a broad consensus. In response to this need, a consensus development core group, comprising (paediatric) nephrologists, (paediatric) urologists, biochemists and geneticists from OxalEurope and the European Rare Kidney Disease Reference Network (ERKNet), formulated and graded statements relating to the management of PH on the basis of existing evidence. Consensus was reached following review of the recommendations by representatives of OxalEurope, ESPN, ERKNet and ERA, resulting in 48 practical statements relating to the diagnosis and management of PH, including consideration of conventional therapy (conservative therapy, dialysis and transplantation), new therapies and recommendations for patient follow-up.

HOGA1 gene pathogenic variants in primary hyperoxaluria type III: Spectrum of pathogenic sequence variants, and phenotypic association

Primary hyperoxalurias (PH) are a group of rare heterogeneous disorders characterized by deficiencies in glyoxylate metabolism. To date, three genes have been identified to cause three types of PH (I, II, and III). The HOGA1 gene caused type III in around 10% of the PH cases. Disease-associated pathogenic variants have been reported from several populations and a comprehensive spectrum of these mutations and genotype-phenotype correlation has never been presented. In this study, we describe new cases of the HOGA1 gene pathogenic variants identified in our population. We report the first case of ESKD with successful kidney transplantation with 5 years of follow-up. Furthermore, a comprehensive overview of PH type III associated HOGA1 gene variants was carried out. Compiling the data from the literature, we reviewed 57 distinct HOGA1 gene pathogenic variants in 175 patients worldwide. The majority of reported variants are missense variants that predicted a loss of function mechanism as the underlying pathology. There has been evidence of the presence of founder mutations in several populations like Europeans, Ashkenazi Jews, Arab, and Chinese populations. No significant genotype-phenotype correlation was identified concerning the ages of onset of the disease and biochemical and metabolic parameters. Nephrocalcinosis was rare in patients with disease-associated variants. Most of the patients were presented with urolithiasis early in life; only five cases reported disease progression after the second decade of life. The establishment of impairment of renal function in 8% of all the reported cases makes this type a relatively severe form of primary hyperoxaluria, not a benign etiology as suggested previously.

A Cluster of Metabolic-Related Genes Serve as Potential Prognostic Biomarkers for Renal Cell Carcinoma

Renal cell carcinoma (RCC) is the most common type of renal cancer, characterized by the dysregulation of metabolic pathways. RCC is the second highest cause of death among patients with urologic cancers and those with cancer cell metastases have a 5-years survival rate of only 10–15%. Thus, reliable prognostic biomarkers are essential tools to predict RCC patient outcomes. This study identified differentially expressed genes (DEGs) in the gene expression omnibus (GEO) database that are associated with pre-and post-metastases in clear cell renal cell carcinoma (ccRCC) patients and intersected these with metabolism-related genes in the Kyoto encyclopedia of genes and genomes (KEGG) database to identify metabolism-related DEGs (DEMGs). GOplot and ggplot packages for gene ontology (GO) and KEGG pathway enrichment analysis of DEMGs with log (foldchange) (logFC) were used to identify metabolic pathways associated with DEMG. Upregulated risk genes and downregulated protective genes among the DEMGs and seven independent metabolic genes, RRM2, MTHFD2, AGXT2, ALDH6A1, GLDC, HOGA1, and ETNK2, were found using univariate and multivariate Cox regression analysis, intersection, and Lasso-Cox regression analysis to establish a metabolic risk score signature (MRSS). Kaplan-Meier survival curve of Overall Survival (OS) showed that the low-risk group had a significantly better prognosis than the high-risk group in both the training cohort (p < 0.001; HR = 2.73, 95% CI = 1.97–3.79) and the validation cohort (p = 0.001; HR = 2.84, 95% CI = 1.50–5.38). The nomogram combined with multiple clinical information and MRSS was more effective at predicting patient outcomes than a single independent prognostic factor. The impact of metabolism on ccRCC was also assessed, and seven metabolism-related genes were established and validated as biomarkers to predict patient outcomes effectively.

Improving Treatment Options for Primary Hyperoxaluria

The primary hyperoxalurias are three rare inborn errors of the glyoxylate metabolism in the liver, which lead to massively increased endogenous oxalate production, thus elevating urinary oxalate excretion and, based on that, recurrent urolithiasis and/or progressive nephrocalcinosis. Frequently, especially in type 1 primary hyperoxaluria, early end-stage renal failure occurs. Treatment possibilities are scare, namely, hyperhydration and alkaline citrate medication. In type 1 primary hyperoxaluria, vitamin B6, though, is helpful in patients with specific missense or mistargeting mutations. In those vitamin B6 responsive, urinary oxalate excretion and concomitantly urinary glycolate is significantly decreased, or even normalized. In patients non-responsive to vitamin B6, RNA interference medication is now available. Lumasiran® is already available on prescription and targets the messenger RNA of glycolate oxidase, thus blocking the conversion of glycolate into glyoxylate, hence decreasing oxalate, but increasing glycolate production. Nedosiran blocks liver-specific lactate dehydrogenase A and thus the final step of oxalate production. Similar to vitamin B6 treatment, where both RNA interference urinary oxalate excretion can be (near) normalized and plasma oxalate decreases, however, urinary and plasma glycolate increases with lumasiran treatment. Future treatment possibilities are on the horizon, for example, substrate reduction therapy with small molecules or gene editing, induced pluripotent stem cell-derived autologous hepatocyte-like cell transplantation, or gene therapy with newly developed vector technologies. This review provides an overview of current and especially new and future treatment options.

The genetics of kidney stone disease and nephrocalcinosis

Kidney stones (also known as urinary stones or nephrolithiasis) are highly prevalent, affecting approximately 10% of adults worldwide, and the incidence of stone disease is increasing. Kidney stone formation results from an imbalance of inhibitors and promoters of crystallization, and calcium-containing calculi account for over 80% of stones. In most patients, the underlying aetiology is thought to be multifactorial, with environmental, dietary, hormonal and genetic components. The advent of high-throughput sequencing techniques has enabled a monogenic cause of kidney stones to be identified in up to 30% of children and 10% of adults who form stones, with ~35 different genes implicated. In addition, genome-wide association studies have implicated a series of genes involved in renal tubular handling of lithogenic substrates and of inhibitors of crystallization in stone disease in the general population. Such findings will likely lead to the identification of additional treatment targets involving underlying enzymatic or protein defects, including but not limited to those that alter urinary biochemistry.

Diet-related urine collections: assistance in categorization of hyperoxaluria

Hyperoxaluria, one of the major risk factors for calcium oxalate urolithiasis and nephrocalcinosis, causes significant morbidity and mortality and should therefore be detected and treated as soon as possible. An early, consequent and adequate evaluation, but also a distinction between primary (PH) and secondary hyperoxaluria (SH) is therefore essential. We evaluated the usefulness of three consecutive 24-h urine collections under different diets [usual diet, (A), low oxalate diet, (B), high oxalate diet, (C)] to prove SH, or to find evidence of PH by changes in urinary oxalate excretion (Uox). We retrospectively analyzed results from 96 pediatric patients (47 females and 49 males, age 3–18 years) who presented with a history of nephrolithiasis, nephrocalcinosis and/or persistent hematuria in whom hyperoxaluria was found in an initial urine sample. The typical pattern of SH was found in 34 patients (mean Uox (A) 0.85 ± 0.29, (B) 0.54 ± 0.15 and (C) 0.95 ± 0.28 mmol/1.73m²/d). PH was suspected in 13 patients [(A) 1.21 ± 0.75; (B) 1.47 ± 0.51 and (C) 1.60 ± 0.82 mmol/1.73m²/d], but genetically proven only in 1/5 patients examined. No hyperoxaluria was found in 16 patients. Data were inconclusive in 33 patients. Urine collection under different diets is helpful to diagnose secondary hyperoxaluria and may provide evidence, that urinary oxalate excretion is normal. We have now established this procedure as our first diagnostic step before further, more extensive and more expensive evaluations are performed.

Possible ethnic associations in primary hyperoxaluria type-III-associated HOGA1 sequence variants

Primary hyperoxaluria type-III is a disorder of glyoxylate metabolism, caused by pathogenic variants in the HOGA1 gene. To date more than 50 disease-associated pathogenic sequence variants are identified in the gene. A few of the variants are population specific and are considered to have a founder effect in respective populations. The most prevalent variant, c.700+5G>T, identified frequently in Caucasian (allele frequency 0.63) and European (0.35) populations. Two variants, c.860G>T (p.Gly287Val) and c.944_946delAGG (p.Glu315del), account for 95% of the allele count in patients of Ashkenazi Jews ancestry. A possible mutational hot-spot at c.834 position is frequently found mutated in Chinese patients. This observed ethnic associations of HOGA1 alleles span a spectrum ranging from recurrence limited to an ethnic group to a possible founder-effect.

A report from the European Hyperoxaluria Consortium (OxalEurope) Registry on a large cohort of patients with primary hyperoxaluria type 3

Outcome data in primary hyperoxaluria type 3 (PH3), described as a less severe form of the PH's with a low risk of chronic kidney disease, are scarce. To investigate this, we retrospectively analyzed the largest PH3 cohort reported so far. Of 95 patients, 74 were followed over a median of six years. Median age of first symptoms and diagnosis were 1.9 and 6.3 years, respectively. Urolithiasis was the major clinical feature observed in 70% of pediatric and 50% of adult patients. At most recent follow-up available for 56 of the 95 patients, 21.4% were in chronic kidney disease stages 2 or more. For better characterization, samples from 49 patients were analyzed in a single laboratory and compared to data from patients with PH1 and PH2 from the same center. Urinary oxalate excretion was not significantly different from PH1 and PH2 (median: 1.37, 1.40 and 1.16 mmol/1.73m²/24hours for PH1 not responsive to vitamin B6, PH2, and PH3, respectively) but was significantly higher than in vitamin B6 responsive patients with PH1. Urinary oxalate excretion did not correlate to stone production rate nor to estimated glomerular filtration rate. Normocitraturia was present even without alkalinisation treatment; hypercalciuria was found rarely. Median plasma oxalate was significantly different only to the vitamin B6-unresponsive PH1 group. Thus, PH3 is more comparable to PH1 and PH2 than so far inferred from smaller studies. It is the most favorable PH type, but not a benign entity as it constitutes an early onset, recurrent stone disease, and kidney function can be impaired.

Clinical characterization of primary hyperoxaluria type 3 in comparison to types 1 and 2: a retrospective cohort study

BACKGROUND

Primary hyperoxaluria type 3 (PH3) is caused by mutations in the HOGA1 gene. PH3 patients often present with recurrent urinary stone disease (USD) in first decade of life, but prior reports suggested PH3 may have a milder phenotype in adults. The current study characterized clinical manifestations of PH3 across the decades of life in comparison to PH1 and PH2.

METHODS

Clinical information was obtained from the Rare Kidney Stone Consortium Primary Hyperoxaluria Registry (PH1 n = 384; PH2 n = 51; PH3 n = 62).

RESULTS

PH3 patients presented with symptoms at a median 2.7 yrs old compared to PH1 (4.9 yrs) and PH2 (5.7 yrs) (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 to PH1 and PH2 (1.1 vs 1.6 and 1.5 mmol/day/1.73m2, respectively, p < 0.001) while urine calcium was highest in PH3 (112 vs 51 and 98 mg/day/1.73m2 in PH1 and PH2, respectively, p < 0.001). Stone events per decade of life were similar across the age span and the 3 PH types. At 40 years of age, 97% of PH3 patients had not progressed to ESKD compared to 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.

Plasma oxalate levels in primary hyperoxaluria type I show significant intra-individual variation and do not correlate with kidney function

BACKGROUND

Primary hyperoxalurias are rare diseases with endogenous overproduction of oxalate, thus leading to hyperoxaluria, hyperoxalemia, urolithiasis, and/or nephrocalcinosis and eventually early kidney failure. Plasma oxalate (POx) is an important diagnostic parameter in clinical studies on primary hyperoxaluria (PH). This is especially the case in kidney failure, where urinary parameters are no longer suitable. We aimed to evaluate whether POx would be an adequate endpoint for clinical studies in PH patients with stable kidney function. In addition, the correlation of POx to serum creatinine (SCr) and calculated glomerular filtration rate (eGFR) was examined.

METHODS

We retrospectively analyzed follow-up of individual POx values over time, as well as POx correlation to SCr, eGFR, and vitamin B6 (VB6), a common therapeutic in PH1. Results from 187 blood samples taken between 2009 and 2017, during routine laboratory evaluations from 41 patients with PH1 who had neither undergone dialysis nor transplantation, were evaluated.

RESULTS

Negligibly low correlation coefficients (CCs) between POx vs. SCr (CC = -0.0950), POx vs. eGFR (CC = -0.1237), and POx vs. VB6 (CC = 0.1879) were found, with the exception of CKD stage 3a patients, who showed a positive correlation (CC of - 0.7329, POx vs eGFR). The intra-individual analysis of POx over time showed a high fluctuation of POx values.

CONCLUSION

We conclude that POx has a limited validity as a primary endpoint for clinical studies in PH1 patients with stable kidney function. In addition, it does not correlate to SCr and eGFR in this group of patients.

Inherited conditions resulting in nephrolithiasis

PURPOSE OF REVIEW

Prevalence of pediatric urolithiasis is increasing, which is definitively visible in increasing numbers of presentations in emergency or outpatient clinics. In pediatric patients, a genetic or metabolic disease has to be excluded, so that adequate treatment can be installed as early as possible. Only then either recurrent stone events and chronic or even end-stage kidney disease can be prevented.

RECENT FINDINGS

The genetic background of mostly monogenic kidney stone diseases was unravelled recently. In hypercalcuria, for example, the commonly used definition of idiopathic hypercalciuria was adopted to the genetic background, here three autosomal recessive hereditary forms of CYP24A1, SLC34A1 and SLC34A3 associated nephrocalcinosis/urolithiasis with elevated 1.25-dihydroxy-vitamin D3 (1.25-dihydroxy-vitamin D3) (calcitriol) levels. In addition either activating or inactivating mutations of the calcium-sensing receptor gene lead either to hypocalcemic hypercalciuria or hypercalcemic hypocalciuria. In primary hyperoxaluria, a third gene defect was unravelled explaining most of the so far unclassified patients. In addition, these findings lead to new treatment options, which are currently evaluated in phase III studies.

SUMMARY

Kidney stones are not the disease itself, but only its first symptom. The underlying disease has to be diagnosed in every pediatric patient with the first stone event.

Nine novel HOGA1 gene mutations identified in primary hyperoxaluria type 3 and distinct clinical and biochemical characteristics in Chinese children

BACKGROUND

Primary hyperoxaluria type 3 (PH3) is characterized by mutations in the 4-hydroxy-2-oxoglutarate aldolase (HOGA1) gene. PH3 patients are thought to present with a less severe phenotype than PH1 and PH2 patients. However, the clinical characteristics of PH3 patients have yet to be defined in sufficient detail. The aims of this study were to report HOGA1 mutations of PH3 in Chinese children, and to analyze the genotype and clinical characteristics of these PH3 patients.

METHODS

Genetic analysis (targeted gene panel-based and/or whole-exome sequencing) of HOGA1 was performed in 52 patients with a high suspicion of PH3, and DNA was obtained from the patient and both the parents. The clinical, biochemical, and genetic data of these 12 patients identified with HOGA1 mutations were subsequently retrospectively reviewed.

RESULTS

These 12 patients were identified with HOGA1 mutation. The median onset of clinical symptoms was 18.25 (range 5-38) months. In total, 14 different mutations were identified including 9 novel mutations in these 12 patients with PH3. All of these 12 patients initially presented with urolithiasis, and 3 patients among them comorbid urinary tract infection (UTI) as another initial symptom. Ten patients experienced hyperoxaluria (average oxalate 0.77 mmol/1.73 m²/24h). In contrast, urine calcium excretion was normal in 8 patients and 2 patients with hypercalciuria (urine calcium > 4 mg/kg/24 h). At the time of diagnosis, estimated GFR was 155.6 ml/min per 1.73 m², and at last follow-up time (17.3 months later from diagnosis on average), estimated GFR was 157.5 ml/min per 1.73 m². To date, none of the patients has impaired renal function based on and progressed to ESRD.

CONCLUSIONS

We found that PH3 was significantly diagnosed in our urolithiasis patients during childhood. Nine novel HOGA1 mutations were identified in association with PH3, which provide a first-line investigation in Chinese PH3 patients. The eGFR was normal in all children with PH3. This finding is in contrast to the early impairment of renal function in PH1 and PH2.

Mutation Hot Spot Region in the HOGA1 Gene Associated with Primary Hyperoxaluria Type 3 in the Chinese Population

BACKGROUND

Primary hyperoxaluria type 3 (PH3) is a rare autosomal recessive disorder that affects glyoxylate metabolism. PH3 is caused by defects in 4-hydroxy-2-oxoglutarate aldolase, which is encoded by the HOGA1 gene. However, only 3 cases of PH3 have been described in Asians until today. This study aimed to determine the clinical and mutation spectra of patients from mainland China with PH3.

METHODS

We applied targeted next-generation sequencing to four non-consanguineous, unrelated Chinese families with PH3 to identify the genes hosting disease-causing mutations. This approach was confirmed by Sanger sequencing.

RESULTS

Five patients (2 boys and 3 girls) from four unrelated Chinese families were admitted because of kidney stones. Five HOGA1 gene sequence mutations were detected, including two novel mutations, c.811C>T (p.R271C) and c.812G>A (p.R271H). These compound heterozygous mutations were detected in a female PH3 patient (patient 4). Other patients included 2 boys who had heterozygous c.834_834+1GG>TT and c.834G>A (p.A278A) mutations (patients 1 and 2), a girl with homozygous c.834G>A (p.A278A) mutation (patient 3), and a girl with heterozygous c.834_834+1GG>TT and c.346C>T (p.Q116X) mutations (patient 5). The mutations in the c.834_834+1 region, including c.834G>A, c.834+1G>T, and c.834_834+1GG>TT, account for 5/8 of alleles in our study and 3/4 of alleles reported among Chinese patients. All patients in this study received hyperhydration and urine alkalinization treatment.

CONCLUSION

Five PH3 cases were reported. Potential mutation hot spot region (c.834_834+1) in the Chinese population and two novel mutations were found.

Genetische Nierensteinerkrankungen

Die Inzidenz und Prävalenz von Steinerkrankungen haben in den letzten Jahren deutlich zugenommen. Es ist von entscheidender Bedeutung, möglichst frühzeitig eine richtige Diagnose der zugrunde liegenden Erkrankung zu stellen, um die richtige Therapie einzuleiten und damit möglicherweise schwerwiegende Folgen, wie terminales Nierenversagen, zu verhindern. Bei Kindern lassen sich in ca. 75 % der Fälle genetische oder anatomische Ursachen identifizieren. Die verschiedenen zugrunde liegenden Erkrankungen für die jeweiligen lithogenen Risikofaktoren werden hier präsentiert und die entsprechenden Therapieoptionen, sofern vorhanden, erläutert.

Rapid liquid chromatography tandem mass-spectrometry screening method for urinary metabolites of primary hyperoxaluria

Background

The primary hyperoxalurias are inherited disorders of glyoxylate metabolism that lead to overproduction of oxalate, urolithiasis and renal failure. Delays in diagnosis can be costly in terms of preserving renal function. Here we present a rapid liquid chromatography tandem mass-spectrometry screening method for the analysis of metabolites (primary hyperoxaluria metabolites) produced in excess by primary hyperoxaluria patients that include glycolate, glycerate and 2,4-dihydroxyglutarate.

Methods

Assay performance was compared to our existing gas chromatography–mass spectrometry method and clinical utility established by analysis of urine samples from patients with confirmed primary hyperoxalurias (11 PH1, 12 PH2 and 8 PH3) and controls ( n = 12). An additional 67 urine samples from patients with PH3 were used postvalidation to confirm the derived 2,4-dihydroxyglutarate cut-off.

Results

Glycolate, glycerate and 2,4-dihydroxyglutarate showed a mean bias of 3.3, −22.8 and 5.7%, respectively, compared to our previously published gas chromatography–mass spectrometry method. The mean total imprecision for glycolate, glycerate and 2,4-dihydroxyglutarate was shown to be 6.4, 10 and 11%, respectively. Clinical assessment confirmed that mean urinary glycolate, glycerate and 2,4-dihydroxyglutarate excretion were significantly elevated in patients with PH1, PH2 and PH3, respectively. The greatest sensitivity and specificity for PH1, PH2 and PH3 was achieved at cut-offs of 193, 100 and 4.9 μmol/mmol for glycolate, glycerate and 2,4-dihydroxyglutarate, respectively.

Conclusions

A rapid screening method for the identification and differentiation of patients with suspected PH1, PH2 and PH3 is presented that allows focussing of genetic testing, saving time, money and, with earlier treatment, potential preservation of renal function for these patients.

Translation inhibition corrects aberrant localization of mutant alanine-glyoxylate aminotransferase: possible therapeutic approach for hyperoxaluria

Primary hyperoxaluria type 1 is a severe kidney stone disease caused by abnormalities of the peroxisomal alanine-glyoxylate aminotransferase (AGT). The most frequent mutation G170R results in aberrant mitochondrial localization of the active enzyme. To evaluate the population of peroxisome-localized AGT, we developed a quantitative Glow-AGT assay based on the self-assembly split-GFP approach and used it to identify drugs that can correct mislocalization of the mutant protein. In line with previous reports, the Glow-AGT assay showed that mitochondrial transport inhibitors DECA and monensin increased peroxisomal localization of the mutant. Here, we demonstrate that prolonged treatment with the translation elongation inhibitor emetine, a medicinal alkaloid used in treatment of amoebiasis, corrected G170R-AGT mislocalization. Furthermore, emetine reduced the augmented oxalate level in culture media of patient-derived hepatocytes bearing the G170R mutation. A distinct translation inhibitor GC7 had a similar effect on the mutant Glow-AGT relocalization indicating that mild translation inhibition is a promising therapeutic approach for primary hyperoxaluria type 1 caused by AGT misfolding/mistargeting.

KEY MESSAGES

• There is no effective conservative treatment to decrease oxalate production in PH1 patients. • Chemical chaperones rescue mislocalization of mutant AGT and reduce oxalate levels. • We have developed an assay for precise monitoring of the peroxisomal AGT. • Inhibition of translation by emetine reroutes the mutant protein to peroxisome. • Mild translation inhibition is a promising cure for conformational disorders.