Neurological impairment occurred in 44% of patients, with worse neurological outcomes observed in patients with argininosuccinate lyase deficiency, arginase 1 deficiency, hyperornithinemia-hyperammonemia-homocitrullinuria, EO presentations, pre-2014 diagnosis, and patients with higher levels of ammonia at diagnosis. This evidence concerns the gene ARG1 and Hyperornithinemia.