Abstract
Alpha-1 antitrypsin deficiency is characterized by reduced serum AAT level due to mutations in the SERPINA1 gene, resulting in reduced protein level or altered functionality. There are also null alleles leading to truncated proteins, unstable transcription or mRNA degradation. AAT expression is controlled by different promoters, mainly for hepatocytes or monocytes. Transcription in hepatocytes starts in exon 1C while monocytes can transcribe from exon 1A. Non-coding exons 1A, 1B and 1C can be alternatively spliced to join exon 2, and then different alternative spliced transcripts occur in the AAT gene expression.
We aimed to quantify the different transcription products generated from exon 1A (monocytes) or 1C (hepatocytes) to better measure AAT expression, and to study how different mutations affect transcription.
We have developed a method to quantitatively analyze different transcription fragments of the AAT gene by using quantitative PCR (QT-PCR). Transcripts including the exon 1A/2 or 1C/2 were analyzed in a set of 15 peripheral blood samples from AAT deficiency patients with different mutations and compared to expression in normal controls. Levels of expression of these transcripts were correlated with their genotypes and serum AAT protein levels.
Significant reduction in the expression of the 1C transcript but not in the 1A transcript was found in cases carrying null alleles such as Mattawa or Porto. However, cases with deficient mutations such as Z or Malton were not associated to reduction in the mRNA levels of the transcripts analyzed either 1C or 1A.
This is a new analysis tool to investigate how different mutations in the AAT gene might affect expression at transcription level.
- © 2014 ERS