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.