Genetic defects in the liver phosphorylase system in Argentine patients nosological definition through a strategy of enzimatic and molecular analysis

Abstract

The phosphorylase and phosphorylase-b kinase (PHK) deficiencies in the liver constitute the phosphorylase system defects (PSD), leading to Glycogenosis Type VI (GSD-VI) and Type IX (GSD-IX), respectively. The hepatic phosphorylase is encoded by PYGL gene. GSD-IX are caused by a genetic defect in one of the hepatic PHK subunits encoded by PHKA2, PHKG2 and PHKB genes, respectively. The PHK deficiency linked to the X chromosome (PHKA2 gene) presents two enzymatic variants: XLG1 (reduced in liver and erythrocytes) and XLG2 (only decreased in liver). The aim of this work is to define nosologically PSD taking into account the gender of the patient, PHK activity in erythrocytes, and molecular analysis of the PYGL gene. 2 women and 16 men (14 unrelated families) were studied. PHK activity in erythrocytes resulted deficient in 14 male patients and was normal in two male probands (still without diagnostic definition) and in the 2 women. In these latter patients, the molecular anaylisis of the PYGL gene identified two novel missense mutations, p.Gly233Ser and p.Gly686Arg, and the IVS15-2delA polymorphism. The allele frequency of P.Gly686Arg was 75%. The in silico studies predict that both new mutations would affect the enzyme functionality. This study allowed the accurate diagnosis of GSD-VI (2/2) and GSD-IX (14/16). The molecular analysis of the PHKA2 gene, responsible for EAG-IX linked to the X chromosome, is currently in progress in our Center. This research represents a continuity of the Project for the exact definition of PSD, unprecedented area of knowledge in our country.