Argininosuccinate lyase deficiency:: Mutational spectrum in Italian patients and identification of a novel ASL pseudogene

Argininosuccinic aciduria (ASAuria) is an inborn error of metabolism caused by mutations in the argininosuccinate lyase (ASL) gene, which leads to the accumulation of argininosuccinic acid (ASA) in body fluids and severe hyperammonemia. A severe neonatal form and a milder late,onset variant are described. We report a novel ASL pseudogene located in the centromeric region of chromosome 7, 14 novel mutations in the ASL gene, and a novel intronic polymorphism found in a cohort of Italian patients. Our approach relied exclusively on genomic DNA analysis. We found seven missense mutations, two nonsense, three small insertions/deletions, and two splicing mutations. Only two patients harbored previously described mutations, and among the novel variants only two were present in more than one kindred. The pathogenicity of the splicing mutations was demonstrated by a functional splicing assay that employed a hybrid minigene. We also performed molecular modeling using the reported three, dimensional structure of ASL to predict the functional consequences of the missense mutations. There was no genotype-phenotype correlation. Patients with neonatal onset display developmental delay and seizures despite adequate metabolic control. Moreover, hepatomegaly, fibrosis, and abnormal liver function tests are common complications in these patients, but not in patients with the late infancy form. We stress the importance of mutation analysis in patients with ASAuria, to confirm the clinical diagnosis, and to perform DNA-based prenatal diagnosis in future pregnancies of these families.