RESUMO
We report on 21 male patients who presented after 28 days of age with ornithine transcarbamylase (OTC) deficiency, which we define as late-onset OTC deficiency. These patients appeared normal at birth, but irritability, vomiting, and lethargy, which were often episodic, later developed. The age at presentation ranged from 2 months to 44 years. Biochemical testing revealed hyperammonemia, hyperglutaminemia, hypocitrullinemia, increased urinary orotate excretion, and decreased liver OTC activity measured in vitro, which ranged from 0% to 15% of normal. Male patients who were older at presentation had a somewhat different pattern of presenting symptoms and were more likely to die. These data illustrate the phenotypic variability of OTC deficiency. Unexplained episodes of repetitive or protracted vomiting in association with progressive alterations in behavior or neurologic findings should suggest the diagnosis of a urea cycle defect (or another symptomatic inborn error of metabolism), regardless of the age or medical history of the patient.