Current status of primary hyperoxaluria type 1 in Japan

Primary hyperoxaluria (PH) is a rare autosomal recessive disorder characterized by an abnormal increase in urinary oxalate excretion. Primary hyperoxaluria type 1 (PH1), the most common PH subtype, is caused by a deficiency of the liver-specific enzyme alanine:glyoxylate aminotransferase, which is localized to peroxisomes. In Japan, the status of PH1 has not been studied in two decades, and few longitudinal studies of PH1 patients have been conducted worldwide. This study aims to analyze the present situation regarding PH1 in Japan. We conducted a literature review of PH1 cases reported in Japan between 2003 and 2023. Twenty patients were diagnosed with PH1 during the study period, including 7 males, 12 females, and 1 patient with an unspecified sex. The median ages at symptom onset and diagnosis were 4.21 years (range: 0.17-47) and 5.5 years (range: 0.17-43), respectively. Ten patients (50%) were diagnosed before age 18, four (44%) of whom had already progressed to end-stage renal disease (ESRD). Among the six patients diagnosed after 18 years, all had ESRD or progressed to ESRD soon after diagnosis. The overall survival (OS) rate was 81% at 5, 10 and 20 years post-diagnosis. The mean observation period was 5.62 years (range: 0-32.6). Few longitudinal studies on PH1 patients have been conducted in Japan or worldwide. Over the past 20 years, the median ages at both symptom onset and diagnosis have significantly decreased, and the OS rate has increased. Early diagnosis and intervention may contribute to better outcomes for PH1 patients in Japan.