New therapeutics are needed to address the rapid progression of calcium oxalate (CaOx) nephrolithiasis and life-threatening kidney failure afflicting infants and young adults with one of the three different genetic types of Primary Hyperoxaluria (PH) types 1, 2, and 3. Glyoxylate and hydroxypyruvate reductase knockout (Grhpr KO) mice recapitulate the pathophysiology of PH type 2 (PH2), developing accelerated hyperoxaluria and CaOx kidney stone formation. Previous studies have shown that this process can be mitigated by introducing an additional genetic knockout of the liver and kidney mitochondrial enzyme, hydroxyproline dehydrogenase (Hypdh/Prodh2), which is responsible for the first step in liver production of glyoxylate and oxalate. Using Grhpr KO mice, we evaluated N-propargylglycine (N-PPG) as a preclinical candidate for PH2, measuring oxalate levels, CaOx stone formation, Cystatin C levels, albumin/creatinine ratio, kidney tubule damage by kidney injury molecule-1 and Lotus Tetragonolobus lectin immunohistochemistry, metabolites, weight, and lifespan. Oral administration of N-PPG, a well-tolerated small-molecule inhibitor of Hypdh/Prodh2, significantly reduces hyperoxaluria and weight loss in Grhpr KO mice within three weeks, while preventing CaOx stone formation and kidney tubular damage. In a 24-week survival study during which vehicle-treated Grhpr KO mice exhibit a median survival of only 15 weeks, daily treatment with N-PPG fully restores weight and survival in the Grhpr KO mice to that of wild-type control mice. N-PPG suppressed hyperoxaluria during this extended treatment period, preventing CaOx stone formation, kidney tubule injury and loss of kidney function, achieving beneficial outcomes in this PH2 mouse model comparable to controls. Our findings establish N-PPG as a promising therapeutic candidate for the long-term prevention of CaOx kidney stone formation and kidney failure complications in PH2.

Primary hyperoxaluria type 2 is a rare genetic disorder of oxalate due to a defect in the glyoxalate reductase/hydroxypyruvate reductase enzyme. This study aimed to describe the characteristics and outcomes in a pediatric population from a single center in Pakistan. This study was conducted at the Sindh Institute of Urology and Transplantation (SIUT), Karachi, from January 2010 to December 2022, involving children under 18 years with nephrocalcinosis. Data collected included demographics, clinical features, laboratory findings, imaging results, family history of kidney stones, and consanguinity. Genetic testing, including next-generation sequencing and Sanger sequencing, was performed, and patients were followed for 24 months to monitor the progression of chronic kidney disease (CKD) stages. Fifty-two children were diagnosed with primary hyperoxaluria type 2 (PH2) confirmed by genetic testing. The majority were male (56%), between 5 and 10 years of age (46%), and from the Sindh province (62%). Seventeen distinct GRHPR gene mutations were identified, predominantly missense variants. The most frequent mutation was Gly165Asp (observed in 12 patients), followed by Leu6Phe and Trp138Arg (8 and 7 patients, respectively). Six of the identified mutations were novel. At presentation, 30% of children were in CKD stage 5, and this proportion increased to 42% after 24 months of follow-up. Male sex and higher baseline serum creatinine were significant predictors of progression to CKD stage 5. This is the first reported PH2 cohort from Pakistan, highlights a significant disease burden with diverse GRHPR mutations, with most patients presenting in advanced CKD stage 5 at diagnosis.

This research delves into Primary Hyperoxaluria Type 2 (PH2), an autosomal recessive disorder precipitated by a unique case of compound heterozygous deleterious mutations in the GRHPR gene, specifically the intron2/3 c.214-2 T > G and the exon8 c.864-865delTG, leading to a premature stop codon at p.Val289fsTer22. The intron 2/3 variant (c.214-2 T > G) is a novel finding and is reported for the first time. These mutations are associated with profound alterations in protein structure and function. Employing patient-derived induced pluripotent stem cells (iPSCs), we have successfully generated a patient-specific model that exhibits the hallmarks of pluripotency, including typical stem cell morphology, expression of pluripotency markers, and a normal karyotype. The iPSCs are capable of differentiating into all three germ layers, underscoring their potential for regenerative medicine. The established iPSC line offers a promising platform for drug screening and regenerative medicine approaches for PH2.

Primary hyperoxaluria (PH) is a rare autosomal recessive disorder of glyoxylate metabolism characterized by hepatic overproduction of oxalate, leading to oxalate nephropathy and systemic oxalosis without early intervention. PH1 contributes to 80% of the cases, while PH2 (10%) and PH3 (10%) being relatively rarer. PH carries a prevalence of one to three per one million population, and PH2 (pathogenic GRHPR gene variant) exhibits high phenotypic heterogeneity, complicating its diagnosis. We present a 17-year-old male who presented with a subacute onset of fever, dyspnea, oliguria, and volume overload for two weeks. Laboratory findings revealed: hemoglobin 5.2 g/dL, urea 194 mg/dL, creatinine 10.6 mg/dL, calcium 5.8 mg/dL, albumin 3.8 g/dL, and bicarbonate 12 mmol/L. Urinalysis showed 10-12 pus cells with significant proteinuria (2256 mg/day). Blood pressure was persistently elevated during hospitalization, and ultrasound revealed small kidneys (right 8.7 × 3.5 cm, left 8.3 × 4.1 cm). Evaluation for secondary causes of hypertension and chronic kidney disease (CKD) in the young patients was unremarkable; however, imaging studies identified nephrocalcinosis and urinalysis confirmed hyperoxaluria (96 mg/day) with elevated plasma oxalate levels (93 μmol/L). Secondary hyperoxaluria was excluded, and genetic analysis for PH confirmed a homozygous missense mutation (c.349T>C) in exon 4 of the GRHPR gene. High suspicion, accurate diagnosis, and timely interventions are mandatory to halt the progression of the disease in PH2. Management remains challenging, often necessitating intensive dialysis and consideration for either isolated kidney or combined liver-kidney transplantation as the definitive cure, with novel therapies such as RNA interference agents currently under investigation.