Clinical characteristics, genetic profile and short-term outcomes of children with primary hyperoxaluria type 2: a nationwide experience.

BACKGROUND: Three types of primary hyperoxaluria (PH) are recognized. However, data on PH type 2 (PH2), caused by defects in the GRHPR gene, are limited. METHODS: We reviewed the medical records of patients < 18 years of age with genetically-proven PH2 from seven centres across India to identify the age of onset, patterns of clinical presentation, short-term outcomes and genetic profile, and to determine if genotype-phenotype correlation exists. RESULTS: We report 20 patients (all with nephrolithiasis or nephrocalcinosis) diagnosed to have PH2 at a median (IQR) age of 21.5 (7, 60) months. Consanguinity and family history of kidney stones were elicited in nine (45%) and eight (40%) patients, respectively. The median (IQR) serum creatinine at PH2 diagnosis was 0.45 (0.29, 0.56) mg/dL with the corresponding estimated glomerular filtration rate being 83 (60, 96) mL/1.73 m2/min. A mutational hotspot (c.494 G > A), rare in Caucasians, was identified in 12 (60%) patients. An intronic splice site variant (c.735-1G > A) was noted in five (25%) patients. Four (20%) patients required surgical intervention for stone removal. Major adverse kidney events (mortality or chronic kidney disease (CKD) stages 3-5) were noted in six (30%) patients at a median (IQR) follow-up of 12 (6, 27) months. Risk factors for CKD progression and genotype-phenotype correlation could not be established. CONCLUSIONS: PH2 should no longer be considered an innocuous disease, but rather a potentially aggressive disease with early age of presentation, and possible rapid progression to CKD stages 3-5 in childhood in some patients. A mutational hotspot (c.494 G > A variant) was identified in 60% of cases, but needs further exploration to decipher the genotype-phenotype correlation.

Pediatric combined living donor liver and kidney transplantation for primary hyperoxaluria type 2.

We report the case of a 12-year-old boy with primary hyperoxaluria type 2 (PH2) presenting with end-stage renal disease and systemic oxalosis who underwent a combined living donor liver and kidney transplant from 3 donors, 1 of whom was a heterozygous carrier of the mutation. Plasma oxalate and creatinine levels normalized immediately following the transplant and remain normal after 18 months. We recommend combined liver and kidney transplantation as the preferred therapeutic option for children with primary hyperoxaluria type 2 with early-onset end-stage renal disease.

Patients with primary hyperoxaluria type 2 have significant morbidity and require careful follow-up.

Primary hyperoxaluria type 2 is a rare inherited disorder of glyoxylate metabolism causing nephrocalcinosis, renal stone formation and ultimately kidney failure. Previously, primary hyperoxaluria type 2 was considered to have a more favorable prognosis than primary hyperoxaluria type 1, but earlier reports are limited by low patient numbers and short follow up periods. Here we report on the clinical, genetic, and biochemical findings from the largest cohort of patients with primary hyperoxaluria type 2, obtained by a retrospective record review of genetically confirmed cases in the OxalEurope registry, a dataset containing 101 patients from eleven countries. Median follow up was 12.4 years. Median ages at first symptom and diagnosis for index cases were 3.2 years and 8.0 years, respectively. Urolithiasis was the most common presenting feature (82.8% of patients). Genetic analysis revealed 18 novel mutations in the GRHPR gene. Of 238 spot-urine analyses, 23 (9.7%) were within the normal range for oxalate as compared to less than 4% of 24-hour urine collections. Median intra-individual variation of 24-hour oxalate excretion was substantial (34.1%). At time of review, 12 patients were lost to follow-up; 45 of the remaining 89 patients experienced chronic kidney disease stage 2 or greater and 22 patients had reached stage 5. Median renal survival was 43.3 years, including 15 kidney transplantations in 11 patients (1 combined with liver transplantation). Renal outcome did not correlate with genotype, biochemical parameters or initially present nephrocalcinosis. Thus, primary hyperoxaluria type 2 is a disease with significant morbidity. Accurate diagnosis by 24-hour urine analysis and genetic testing are required with careful follow-up.

Severe child form of primary hyperoxaluria type 2 - a case report revealing consequence of GRHPR deficiency on metabolism.

BACKGROUND: Primary hyperoxaluria type 2 is a rare monogenic disorder inherited in an autosomal recessive pattern. It results from the absence of the enzyme glyoxylate reductase/hydroxypyruvate reductase (GRHPR). As a consequence of deficient enzyme activity, excessive amounts of oxalate and L-glycerate are excreted in the urine, and are a source for the formation of calcium oxalate stones that result in recurrent nephrolithiasis and less frequently nephrocalcinosis. CASE PRESENTATION: We report a case of a 10-month-old patient diagnosed with urolithiasis. Screening of inborn errors of metabolism, including the performance of GC/MS urine organic acid profiling and HPLC amino acid profiling, showed abnormalities, which suggested deficiency of GRHPR enzyme. Additional metabolic disturbances observed in the patient led us to seek other genetic determinants and the elucidation of these findings. Besides the elevated excretion of 3-OH-butyrate, adipic acid, which are typical marks of ketosis, other metabolites such as 3-aminoisobutyric acid, 3-hydroxyisobutyric acid, 3-hydroxypropionic acid and 2-ethyl-3-hydroxypropionic acids were observed in increased amounts in the urine. Direct sequencing of the GRHPR gene revealed novel mutation, described for the first time in this article c.454dup (p.Thr152Asnfs*39) in homozygous form. The frequent nucleotide variants were found in AGXT2 gene. CONCLUSIONS: The study presents metabolomic and molecular-genetic findings in a patient with PH2. Mutation analysis broadens the allelic spectrum of the GRHPR gene to include a novel c.454dup mutation that causes the truncation of the GRHPR protein and loss of its two functional domains. We also evaluated whether nucleotide variants in the AGXT2 gene could influence the biochemical profile in PH2 and the overproduction of metabolites, especially in ketosis. We suppose that some metabolomic changes might be explained by the inhibition of the MMSADH enzyme by metabolites that increase as a consequence of GRHPR and AGXT2 enzyme deficiency. Several facts support an assumption that catabolic conditions in our patient could worsen the degree of hyperoxaluria and glyceric aciduria as a consequence of the elevated production of free amino acids and their intermediary products.

Ethnic differences in GRHPR mutations in patients with primary hyperoxaluria type 2.

The objective of this study was to investigate ethnic differences in the glyoxylate reductase/hydroxypyruvate reductase (GRHPR) gene in patients with primary hyperoxaluria type 2 (PH2). GRHPR was genotyped in Japanese patients with PH2 and all GRHPR mutations described to date were reviewed in terms of geographic and ethnic association. We identified a novel mutation, a two-nucleotide deletion (c.248_249delTG) in exon 3 creating a premature 'stop' at codon 91. Also, we found that the c.864_865delTG mutation was associated with the rs35891798 single-nucleotide polymorphism. The allelic frequencies of the c.103delG, c.494G>A, c.403_404+2 delAAGT, and c.864_865delTG mutations in PH2 patients were 37.8%, 15.6%, 10.0%, and 10.0%, respectively. All patients with the c.103delG mutation were Caucasian. Patients with the c.494G>A mutation and 78% (7/9) of those with the c.403_404+2 delAAGT mutation were from the Indian subcontinent, whereas those with the c.864_865delTG mutation were Chinese or Japanese. Molecular analysis of GRHPR of four Japanese PH2 patients identified a novel mutation (c.248_249delTG in exon 3). Caucasians with PH2 should be screened for the c.103delG mutation; patients from the Indian subcontinent for c.494G>A; and patients of East Asian origin (particularly) for c.864_865delTG. The prevalence of the latter mutation in PH2 patients from East Asia was 75.0%.

Failure of isolated kidney transplantation in a pediatric patient with primary hyperoxaluria type 2.

PH type 2 is caused by decreased activity of GRHPR enzyme that eventually leads to ESRD and systemic oxalosis. Here, we describe an Iranian pediatric patient with PH2 and early ESRD development who received recommended treatment by undergoing isolated kidney transplantation. Diagnosis criteria included a history of reoccurring calcium oxalate renal stones and elevated oxalate levels combined with liver biopsy and decreased enzymatic activity at age five. ESRD prompted transplantation and was performed at age nine. On Day 12 post-op, his serum creatinine level increased. A graft biopsy showed calcium oxalate crystal deposits in renal tubes with no evidence of acute rejection, which resolved with intensive hydration and administration of a potassium citrate solution. Subsequent biopsies confirmed results found in first biopsy. Despite the immunosuppressive therapy, his serum creatinine level increased again after 11 months. Renal tubular obstruction then led to graft nephrectomy. Pathological analysis of tissue confirmed findings of past biopsies. This was a very rare case of early ESRD in PH2 resulting in a failed isolated kidney transplant. As the GRHPR enzyme is predominantly expressed in liver, we suggest a combined liver-kidney transplant may be beneficial in patients with PH2.

Late-onset retinal oxalosis in primary hyperoxaluria type 2.

Purpose: To report a previously undescribed case of late-onset vision loss due to retinal oxalosis in a patient with primary hyperoxaluria type 2 (PH2). Observations: An 82-year-old female with a history of biopsy-proven oxalate nephropathy developed vision loss 8 months after end stage kidney disease. She developed progressive retinal ischemia secondary to crystal deposition. She was presumed to have retinal oxalosis, and genetic testing confirmed PH2. Her retinopathy occurred once renal clearance fellow below hepatic oxalate production. The only effective treatment is kidney transplantation, but this patient was not a candidate. Conclusions and Importance: To date, this is the most delayed-onset and severe reported case of progressive ischemic retinopathy from PH2. Patients with systemic oxalosis should be referred for genetic testing, as there are new RNA interference treatments approved for other subtypes of primary hyperoxaluria.

Clinical features and mutational spectrum of Chinese patients with primary hyperoxaluria type 2.

Primary hyperoxaluria type 2 (PH2) is a rare hereditary disease that causes nephrolithiasis, nephrocalcinosis and kidney failure. This study aimed to investigate the clinical features and mutational spectrum of Chinese patients with PH2. A retrospective cohort study was performed on PH2 patients admitted to our center over seven years. We also systematically reviewed all the articles on Chinese PH2 patients published from January 2000 to May 2023 and conducted a meta-analysis. A total of 25 PH2 patients (10 from our center and 15 from published studies) were included in this study. The median age of onset in patients from our center was 8.50 (1.00, 24.00) years, and 50% were male. Among the full cohort of 25 Chinese patients, the median age of onset was 8.00 (0.40, 26.00) years, and 64% of them were male. Seven patients progressed to end-stage kidney disease, with a median age of 27.50 (12, 31) years. The cumulative renal survival rates were 100%, 91.67%, 45.83% and 30.56% at 10, 20, 30 and 40 years of age, respectively. A total of 18 different variants were identified, and c.864_865del was the dominant variant, accounting for 57.69% of the total alleles. Patients who were heterozygous for c.864_865del were more susceptible to nephrocalcinosis than those who were homozygous for c.864_865del and those harboring other mutations (83.33% versus 33.3% and 0%, respectively) (p = 0.025). The clinical features and mutational spectrum of Chinese PH2 patients were described. This study helps to expand awareness of the phenotypes and genotypes of Chinese PH2 patients and contributes to the improvement of diagnostic and treatment strategies for PH2 patients.

Simultaneous Liver Kidney Transplantation in a Primary Type 2 Hyperoxaluria With Corrected TOF and Severe Cardiomyopathy: A Case Report.

Background: Primary type 2 hyperoxaluria is a very rare genetic disorder,1,2 where in the progression to renal failure was assumed to be insidious and not very common.3 PH2 is due to deficient glyoxylate reductase/hydroxypyruvate reductase (GRHPR),1,2 which was thought to have extra-hepatic production also.4 The progression to renal failure in these patient subgroups is well documented in the Literature and the role of SLK (simultaneous liver and kidney transplantation) has not been clearly established.8. Method: We present a case report of a young girl with PH2, who successfully underwent SLK, with evidence of reduction in the urine oxalate levels post SLK. Results: PH2, though a rare genetic disease, has a proven potential to progress to chronic renal failure requiring transplantation, renal transplantation alone has not shown any benefit, these patients can be offered SLK as a primary treatment option, to improve the outcomes, this needs further validation with consensus and studies.

Hypercalcemia in an Infant with Primary Hyperoxaluria Type 2: A Novel Association.

Hypercalcemia in infants presents with a variety of clinical features and the etiology of hypercalcemia varies with age. Here we present a case of hypercalcemia in an infant presenting with nephrocalcinosis and nephrolithiasis. Our investigations led us to a diagnosis of primary hyperoxaluria (PH) type 2, a rare metabolic disorder, along with hypercalcemia, a never before reported association. A 9-month-old female presented with urinary tract infection and systemic features requiring hospitalization and parenteral antibiotics. Investigations revealed bilateral medullary nephrocalcinosis. Genetic testing revealed a diagnosis of Primary hyperoxaluria type 2 with two possible mutations. Sanger sequencing of the parents identified the pathogenic mutation in the mother. This is the first report of a genetically proven case of primary hyperoxaluria type 2 associated with hypercalcemia.

Young Male With End-Stage Renal Disease Due to Primary Hyperoxaluria Type 2: A Rare Presentation.

Primary hyperoxaluria type 2 (PH2) is a rare genetic disorder characterized by excessive oxalate production due to glyoxylate metabolism alterations. This case report presents a 26-year-old male with PH2 who experienced recurrent nephrolithiasis since childhood, leading to end-stage renal disease (ESRD). The patient's history prompted genetic testing, which revealed a heterozygous missense variant in the GRHPR gene, confirming PH2. Early genetic diagnosis is crucial for preventing ESRD and planning effective treatments. Patients with PH2 require intensive hemodialysis and may benefit from kidney transplantation. However, even after transplantation, ongoing preventive measures are essential due to the risk of hyperoxaluria-related graft damage. This case highlights the importance of early detection and genetic testing in managing PH2 to delay ESRD and improve patient outcomes.

Hemolytic Uremic Syndrome in an Infant with Primary Hyperoxaluria Type II: An Unreported Clinical Association.

A 6-month-old boy presented with acute renal failure, thrombocytopenia, and severe non-immune hemolytic anemia. Infection by Shiga-like toxin-producing Escherichia coli and other causes of microangiopathic hemolysis were ruled out, leading to a diagnosis of atypical hemolytic uremic syndrome (aHUS). Neither pathogenic variants in HUS-associated genes nor anti-factor H antibodies were identified. Copy number variation analysis uncovered 4 copies of complement factor H related genes, CFHR1-CFHR4, conceivably leading to higher than normal levels of the corresponding proteins. However, this abnormality was also found in the healthy relatives, neither explaining the disease nor the excessive complement deposition on endothelial cells detected by an ex-vivo test. Whole-exome sequencing revealed a pathogenic homozygous variant in GRHPR encoding the glyoxylate and hydroxypyruvate reductase. Recessive GRHPR mutations cause primary hyperoxaluria type 2 (PH2). The presence of renal calculi in the patient and elevated oxalate levels in the urine were consistent with the genetic diagnosis of PH2. We hypothesize that, in this patient, hyperoxaluria caused by the GRHPR genetic defect triggered endothelial perturbation and complement activation, which was amplified by impaired factor H regulatory activity due to the increased -CFHR1-CFHR4 copy numbers, resulting in aHUS.