Arginase 1 (
ARG1) deficiency is a rare
urea cycle disorder (UCD), with an estimated frequency of 1 per 2,200,000 births in Japan. Patients with
ARG1 deficiency develop symptoms in late infancy or pre-school age with progressive
neurological manifestations and sometimes present with severe hepatic disease. We previously investigated the status of UCDs in Japan; however, only one patient was identified as having
ARG1 deficiency. Therefore, we aimed to investigate the current status of patients with
ARG1 deficiency in 2018-2021 because almost 10 years have passed since the previous study. We present the disease history, clinical outcome, and treatment of five surviving patients with
ARG1 deficiency and discuss the features of
ARG1 deficiency in Japan. We found that clinicians often face difficulty in diagnosing
ARG1 deficiency at the early stage of onset because of interpatient variability in onset time and clinical manifestations. Blood
L-arginine and guanidino compounds were considered to be the major factors causing adverse neurodevelopmental outcomes. Therefore, early detection and intervention of
ARG1 deficiency is essential for improved neurodevelopmental outcomes.
Liver transplantation has been considered an effective treatment option that can dramatically improve the quality of life of patients, prior to the
neurological manifestation of symptoms caused by
ARG1 deficiency.