We evaluated GAA, creatine and amino acids concentration on 207 plasma samples from 73 patients with different UCD (Ornithine Transcarbamylase (OTC) deficiency, Argininosuccinate Synthase (ASS) deficiency, Argininosuccinate Lyase (ASL) deficiency and Arginase deficiency) (Table 1). This evidence concerns the gene OTC and argininosuccinic aciduria.