Urinary Oxalate Excretion During Pregnancy in Primary Hyperoxaluria Type 1: A Report of 4 Cases

Primary hyperoxaluria (PH) is a rare genetic disorder characterized by excessive oxalate production due to specific gene defects. PH1 is the most prevalent type, causing recurrent kidney stone disease and often leading to chronic kidney disease and kidney failure. Our previous study suggested that pregnancy did not adversely affect kidney function in female PH patients. In this study, we identified four PH1 cases with urinary oxalate (UOx) measurements during pregnancy from the Rare Kidney Stone Consortium and Oxalosis and Hyperoxaluria Foundation PH registry to investigate UOx levels during pregnancy in PH1 patients. All four showed a decrease in UOx during pregnancy compared to before pregnancy and after delivery. These findings contrast with the general population, where UOx tends to increase during pregnancy due to a simultaneous physiological rise in the glomerular filtration rate. Elucidating the mechanism underlying reduced UOx during pregnancy in PH1 could suggest novel PH therapies. These findings could also impact clinical management and have implications regarding the safety of withholding novel PH1-directed molecular therapies that currently have uncertain safety profiles during pregnancy. We highlight the need for additional data on urinary changes in PH patients and other populations while pregnant to clarify changes in UOx throughout pregnancy.