The second most represented category of diseases was the disorders of amino acid metabolism with 31 subjects (Table 1) who were mainly (14 patients, 45%) affected by Urea cycle disorders and inherited hyperammonemias; in this class, the Argininosuccinate lyase deficiency was the most frequent disease (7 patients, 50%) (OMIM: 207900). This evidence concerns the gene ASL and urea cycle disorder.