Still diagnosed too late and under-recognized? The first comprehensive report on primary hyperoxaluria in Poland.

Primary hyperoxalurias (PHs) are rare disorders leading to overproduction and increased urinary excretion of oxalate. Three monogenic forms (PH1-PH3) were classified. PHs lead to urolithiasis and chronic kidney disease. There are only sparse data on patients with PH from Eastern European countries including Poland. The aim of the study was to evaluate the prevalence, genetic background, and clinical course of PH in the Polish population. This was a retrospective multicenter study including data of all identified and genetically confirmed Polish patients with PH. Between 1998 and 2019, 21 patients with PH were identified, including 13 patients with PH1 (62%), 2 with PH2 (9%), and 6 with PH3 (29%). In those with PH1, the most common mutation was c.508G>A in AGXT and in PH3, c.700+5G>T in HOGA1. Nine patients (69%) developed end‑stage renal disease at a median age of 13 years and 2 died. In 6 (46%) PH1 cases, the diagnosis was made only after patients had progressed to end‑stage renal disease and received isolated kidney transplantation, followed by graft failure. Combined liver‑kidney transplantation was performed in 6 patients with PH1. Two siblings with PH2 showed a milder course with slightly decreased renal function in one, at age of 11 years. Despite infantile onset of urolithiasis, all patients with PH3 at a median age of 10 years maintained normal renal function. The prevalence of PH1 and PH2 in Poland seems to be much lower than in Western countries with PH3 constituting about 30% of all cases. The molecular findings and clinical course are typical, but the underdiagnosis is of concern.