Biomarkers Associated With Future Severe Liver Disease in Children With Alpha-1-Antitrypsin Deficiency.

Background And Aims: Children with alpha-1-antitrypsin deficiency (AATD) exhibit a wide range of liver disease outcomes from portal hypertension and transplant to asymptomatic without fibrosis. Individual outcomes cannot be predicted. Liver injury in AATD is caused by the accumulation in hepatocytes of the mutant Z alpha-1-antitrypsin (AAT) protein, especially the toxic, intracellular polymerized conformation.

Fibrosis, biomarkers and liver biopsy in AAT deficiency and relation to liver Z protein polymer accumulation.

Background And Aims: The course of adults with ZZ alpha-1-antitrypsin deficiency (AATD) liver disease is unpredictable. The utility of markers, including liver biopsy, is undefined.

Methods: A prospective cohort, including protocol liver biopsies, was enrolled to address these questions.

The structural basis for Z α-antitrypsin polymerization in the liver.

The serpinopathies are among a diverse set of conformational diseases that involve the aberrant self-association of proteins into ordered aggregates. α-Antitrypsin deficiency is the archetypal serpinopathy and results from the formation and deposition of mutant forms of α-antitrypsin as "polymer" chains in liver tissue. No detailed structural analysis has been performed of this material.

The molecular species responsible for α -antitrypsin deficiency are suppressed by a small molecule chaperone.

The formation of ordered Z (Glu342Lys) α -antitrypsin polymers in hepatocytes is central to liver disease in α -antitrypsin deficiency. In vitro experiments have identified an intermediate conformational state (M*) that precedes polymer formation, but this has yet to be identified in vivo. Moreover, the mechanism of polymer formation and their fate in cells have been incompletely characterised.

Intrahepatic heteropolymerization of M and Z alpha-1-antitrypsin.

The α-1-antitrypsin (or alpha-1-antitrypsin, A1AT) Z variant is the primary cause of severe A1AT deficiency and forms polymeric chains that aggregate in the endoplasmic reticulum of hepatocytes. Around 2%-5% of Europeans are heterozygous for the Z and WT M allele, and there is evidence of increased risk of liver disease when compared with MM A1AT individuals. We have shown that Z and M A1AT can copolymerize in cell models, but there has been no direct observation of heteropolymer formation in vivo.