Citrullinemia Type 1 is an inherited disorder caused by a deficiency of the enzyme argininosuccinate synthetase. This enzyme is responsible for converting the amino acid citrulline into arginine, which is necessary for the body to produce urea. Without this enzyme, citrulline builds up in the body, leading to a variety of symptoms, including vomiting, lethargy, poor feeding, and seizures. If left untreated, Citrullinemia Type 1 can be fatal. Treatment typically involves a low-protein diet and supplementation with arginine.