Prevalence, Disease Onset and Clinical Outcome in Arginase 1 Deficiency: Cross-Border Surveillance in Germany, Austria, and Switzerland.

Arginase 1 deficiency (ARG1-D) is an ultra-rare urea cycle disorder characterized by progressive spastic paraplegia, developmental delay, epilepsy, and episodic hyperammonemia. Evidence on prevalence and clinical presentation is scarce. Therefore, epidemiology and the phenotypical spectrum were assessed in Germany, Austria, and Switzerland (DACH region). We conducted a questionnaire-based, cross-sectional study of confirmed ARG1-D patients in the DACH region. Patients were stratified into early-diagnosed (newborn screening [NBS] or high-risk family screening [HR]) and diagnosed after symptom onset. We evaluated clinical, biochemical, and therapeutic characteristics of individuals with confirmed ARG1-D. Epidemiological prevalence estimates were derived using national population data. A total of 20 patients were identified (Germany: 12, Austria: 7, Switzerland: 1). Eight were diagnosed early (NBS: 4, HR: 4) and 12 after symptom onset. Symptomatically diagnosed patients (median age 11 years) presented with a broad range of clinical manifestations, specifically progressive spastic paraplegia (67%), epilepsy (58%), dystonia (46%), developmental delay (58%), and hepatopathy (50%). Median age at diagnosis was 35 months in symptomatic patients versus 1 month in early-diagnosed patients (p = 0.03). Estimated pediatric prevalence was 1:1042080 in the DACH region, with high regional differences. Hyperammonemia was reported in 72%. Enzyme therapy had been initiated in 21%; 2 patients underwent liver transplantation. ARG1-D is a rare disease with a prevalence of approximately 1:1000000 individuals, and a complex and progressive clinical phenotype. Detection via NBS or HR allows early diagnosis and treatment initiation, potentially altering the clinical outcome.