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.