Abstract
The classical form of alpha 1-antitrypsin (alpha 1-AT) deficiency is associated with a mutant alpha 1-ATZ molecule that polymerizes in the endoplasmic reticulum (ER) of liver cells. A subgroup of individuals homozygous for the protease inhibitor (PI) Z allele develop chronic liver injury and are predisposed to hepatocellular carcinoma. In this study we evaluated the primary structure of alpha 1-AT in a family in which three affected members had severe liver disease associated with alpha 1-AT deficiency. We discovered that one sibling was a compound heterozygote with one PI Z allele and a second allele, the PI Z + saar allele, bearing the mutation that characterizes alpha 1-ATZ as well as the mutation that characterizes alpha 1-AT Saarbrucken (alpha 1-AT saar). The mutation in PI saar introduces a premature termination codon resulting in an alpha 1-AT protein truncated for 19 amino acids at its carboxyl terminus. Studies of a second sib with severe liver disease and other living family members did not reveal the presence of the alpha 1-AT saar mutation and therefore do not substantiate a role for this mutation in the liver disease phenotype of this family. However, studies of alpha 1-AT saar and alpha 1-ATZ + saar expressed in heterologous cells show that there is prolonged intracellular retention of these mutants even though they do not have polymerogenic properties. These results therefore have important implications for further understanding the fate of mutant alpha 1-AT molecules, the mechanism of ER retention, and the pathogenesis of liver injury in alpha 1-AT deficiency.
Highlights
A subgroup of patients (10%) with the classical form of ␣1-AT1 deficiency are predisposed to chronic hepatitis, cirrhosis, and hepatocellular carcinoma
Using a genetic complementation approach, we found that there is less efficient endoplasmic reticulum (ER) degradation of ␣1-ATZ in cells from some ␣1-AT-deficient individuals who are susceptible to liver disease [16] and, therein, that these individuals have a lesser inherent capacity to respond to, and/or protect themselves from, the hepatotoxic circumstances posed by ER retention of mutant ␣1-ATZ
In this study we examined a potentially informative family in which a pair of sibs had severe liver disease associated with the classical form of ␣1-AT deficiency
Summary
A subgroup of patients (10%) with the classical form of ␣1-AT1 deficiency (homozygous for the PI Z allele) are predisposed to chronic hepatitis, cirrhosis, and hepatocellular carcinoma. The classical form of ␣1-antitrypsin (␣1-AT) deficiency is associated with a mutant ␣1-ATZ molecule that polymerizes in the endoplasmic reticulum (ER) of liver cells. Studies of ␣1-AT saar and ␣1-ATZ ؉ saar expressed in heterologous cells show that there is prolonged intracellular retention of these mutants even though they do not have polymerogenic properties.
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