Polymerase chain reaction for detection of the alpha-1-antitrypsin Z allele in chronic liver disease

The genetic locus for alpha-1-antitrypsin (alpha-AT) is highly polymorphic, but all protein variants are encoded by a single locus on chromosome 14. Periportal hepatocyte granules are described in association with chronic liver disease and the Z variant. A Z-specific point mutation in exon V of the alpha-AT gene, converting amino acid 342 from Glu to Lys, is thought to be responsible for the hepatocyte accumulation. We describe the use of the polymerase chain reaction (PCR) to amplify exon V of the alpha-AT gene and subsequent detection of the wild-type M- and Z-specific sequences by hybridisation to 32P-labelled-allele-specific oligonucleotides. We applied this technique to leucocyte DNA from 37 patients with suspected chronic liver disease, 25 of whom had hepatocyte alpha-AT inclusion granules on liver biopsy. All 25 were homozygous or heterozygous for the Z allele. One patient, phenotyped as PiS, was found to be PiSZ and another phenotyped as PiZ (presumed homozygous), was found to be a Z heterozygote. No Z allele was detected in any of the twelve patients without alpha-AT inclusion granules. This sensitive PCR technique could be used to assess the relative risk of chronic liver disease in PiZ heterozygotes and to determine whether individuals without the Z amino acid 342 substitution can developed periportal alpha-AT granules.