RecruitingLongitudinal Study of Urea Cycle DisordersUrea cycle disorders (UCD) are a group of rare inherited metabolism disorders. Infants and children with UCD commonly experience episodes of vomiting, lethargy, and coma. The purpose of this study is to perform a long-term analysis of a large group of individuals with various UCDs. The study will focus on the natural history, disease progression, treatment, and outcome of individuals with UCD.