Understanding N-Acetyl-L-Glutamate Synthase Deficiency: Mutational Spectrum, Impact of Clinical Mutations on Enzyme Functionality, and Structural Considerations

16 páginas, 5 figuras, 3 tablas. "This is the peer reviewed version of the following article: Hum Mutat. 2016 Jul;37(7):679-94, which has been published in final form at http://dx.doi.org/10.1002/humu.22995. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions"N-acetyl-L-glutamate synthase (NAGS) deficiency (NAGSD), the rarest urea cycle defect, is clinically indistinguishable from carbamoyl phosphate synthetase 1 deficiency, rendering the identification of NAGS gene mutations key for differentiation, which is crucial, as only NAGSD has substitutive therapy. Over the last 13 years, we have identified 43 patients from 33 families with NAGS mutations, of which 14 were novel. Overall, 36 NAGS mutations have been found so far in 56 patients from 42 families, of which 76% are homozygous for the mutant allele. 61% of mutations are missense changes. Lack or decrease of NAGS protein is predicted for ∼1/3 of mutations. Missense mutations frequency is inhomogeneous along NAGS: null for exon 1, but six in exon 6, which reflects the paramount substrate binding/catalytic role of the C-terminal domain (GNAT domain). Correspondingly, phenotypes associated with missense mutations mapping in the GNAT domain are more severe than phenotypes of amino acid kinase domain-mapping missense mutations. Enzyme activity and stability assays with 12 mutations introduced into pure recombinant Pseudomonas aeruginosa NAGS, together with in silico structural analysis, support the pathogenic role of most NAGSD-associated mutations found. The disease-causing mechanisms appear to be, from higher to lower frequency, decreased solubility/stability, aberrant kinetics/catalysis, and altered arginine modulationValencian Government. Grant Number: Prometeo II/2014/029 Science Department of the Spanish Government. Grant Numbers: BFU2011‐30407, BFU2014‐58229‐P Swiss National Science Foundation. Grant Numbers: 310030_127184, 310030_153196Peer reviewe