Rapid analysis of alpha1-antitrypsin PiZ genotype by a real-time PCR approach

alpha1-Antitrypsin (AAT) deficiency is a common inherited cause of emphysema and cirrhotic liver disease. Current laboratory diagnosis of Pi (proteinase inhibitor) status by protein analysis depends on the availability of blood samples and has a limited accuracy. Single-strand conformational polymorphism (SSCP) analysis and direct DNA sequencing can be performed from blood cells or from tissue samples, but it is a time-consuming procedure not suitable for screening purposes. We used a Light-Cycler assisted PCR approach to identify the PiZ mutation and to determine hetero- and homozygous carrier status from whole blood and from paraffin-embedded archival tissue specimens. The results were compared to those obtained by standard PCR amplification followed by SSCP and direct DNA sequencing. Light-Cycler assisted PCR identified heterozygous PiZ mutations in 16 samples, a homozygous PiZ status in three cases, and wild-type PiM in five control samples. In all cases the results were confirmed by SSCP and direct DNA sequencing. Light-Cycler assisted PCR has a high detection rate for the PiZ mutation. It can be performed from blood or from fixed archival tissues, requires only small amounts of DNA, and allows a rapid diagnosis on a high output level.

Chronic liver disease in heterozygous alpha1-antitrypsin deficiency PiZ

BACKGROUND/AIMS

The contribution of the heterozygous state PiZ of alpha1-antitrypsin deficiency (AATD) to the pathogenesis of chronic liver disease is debated. We analyzed whether patients with this genetic defect carrying a single PiZ gene are at increased risk for developing chronic liver disease.

METHODS

1847 consecutive biopsy cases and 1030 autopsy cases of Caucasian adults were screened immunohistochemically for PiZ deposits. The zygosity status was analyzed by single-strand conformational polymorphism (SSCP) and by sequencing DNA extracted from paraffin-embedded tissue.

RESULTS

All analyzed biopsy cases were heterozygous for the PiZ mutation. The biopsy group revealed a significantly higher rate of PiZ-positive cases (3.4%) than the autopsy group (1.8%) (p=0.019). PiZ deposits ranged from scarce granules to extensive globular inclusions as in homozygous AATD of PiZ type. The extent of PiZ deposits correlated well with the inflammatory activity and stage of fibrosis. Cirrhotic livers contained globular PiZ deposits significantly more often than the biopsies with minor fibrosis. PiZ-positive biopsies from patients without concurrent liver disease (n= 26) revealed only minor fibrosis in the age group between 20 and 39 years, but significantly more severe fibrosis and significantly more PiZ deposits in the older age groups. Biopsies with concurrent liver disease (n=28) presented with significantly more severe inflammation and fibrosis, and more PiZ deposits than the cases without concurrent liver disease.

CONCLUSIONS

Patients with heterozygous AATD of PiZ type bear an increased risk for chronic liver disease. If at all, this genetic defect will become clinically relevant only in middle-aged or old adults. It rarely causes liver cirrhosis even without concurrent liver disease. It can aggravate or can be aggravated by advanced coexistent chronic liver diseases. PiZ immunohistochemistry is an easy, highly specific method to detect this metabolic defect on liver biopsies.

Is heterozygous alpha-1-antitrypsin deficiency type PIZ a risk factor for primary liver carcinoma?

BACKGROUND

It is well known that homozygotes with alpha-1-antitrypsin deficiency type PiZ are associated with an increased risk of chronic liver disease and liver carcinoma. The aim of this study was to determine whether heterozygous PiZ status is a risk factor for liver carcinoma development.

METHODS

Three hundred seventeen consecutive primary liver carcinomas and the tumor-bearing liver tissue (tumor series) from adult patients were screened immunohistochemically for hepatocellular PiZ deposits. Liver specimens from 1663 consecutive adult patients (biopsy series) and liver tissue from 1030 consecutive adult autopsies (autopsy series) served as controls. The zygosity status of alpha-1-antitrypsin was verified by analysis of single strand conformational polymorphism and by sequencing DNA extracted from paraffin embedded tissue.

RESULTS

The PiZ frequency in the tumor series (5.99%) was significantly higher than in the biopsy series (3.43%) or the autopsy series (1.84%). Cholangiocarcinomas and/or combined hepatocholangiocarcinomas were seen significantly more frequently in PiZ-associated liver carcinomas (57.9%) than in non-PiZ-associated carcinomas (27.2%). Cirrhosis was found in only 3 of the 19 PiZ-associated carcinomas. The remaining 16 livers showed varying stages of fibrosis or normal tissue. All nine cases with PiZ-associated liver carcinoma suitable for genetic analysis showed heterozygous PiZ mutations.

CONCLUSIONS

Heterozygotes of type PiZ are associated with an increased risk of primary liver carcinoma. PiZ-associated carcinoma may develop in noncirrhotic liver tissue and without concurrent liver disease, and is frequently characterized by cholangiocellular differentiation. The site specific antibody ATZ11 is a reliable morphologic tool for detecting PiZ individuals.

Is heterozygous alpha-1-antitrypsin deficiency type PIZ a risk factor for primary liver carcinoma?

BACKGROUND

It is well known that homozygotes with alpha-1-antitrypsin deficiency type PiZ are associated with an increased risk of chronic liver disease and liver carcinoma. The aim of this study was to determine whether heterozygous PiZ status is a risk factor for liver carcinoma development.

METHODS

Three hundred seventeen consecutive primary liver carcinomas and the tumor-bearing liver tissue (tumor series) from adult patients were screened immunohistochemically for hepatocellular PiZ deposits. Liver specimens from 1663 consecutive adult patients (biopsy series) and liver tissue from 1030 consecutive adult autopsies (autopsy series) served as controls. The zygosity status of alpha-1-antitrypsin was verified by analysis of single strand conformational polymorphism and by sequencing DNA extracted from paraffin embedded tissue.

RESULTS

The PiZ frequency in the tumor series (5.99%) was significantly higher than in the biopsy series (3.43%) or the autopsy series (1.84%). Cholangiocarcinomas and/or combined hepatocholangiocarcinomas were seen significantly more frequently in PiZ-associated liver carcinomas (57.9%) than in non-PiZ-associated carcinomas (27.2%). Cirrhosis was found in only 3 of the 19 PiZ-associated carcinomas. The remaining 16 livers showed varying stages of fibrosis or normal tissue. All nine cases with PiZ-associated liver carcinoma suitable for genetic analysis showed heterozygous PiZ mutations.

CONCLUSIONS

Heterozygotes of type PiZ are associated with an increased risk of primary liver carcinoma. PiZ-associated carcinoma may develop in noncirrhotic liver tissue and without concurrent liver disease, and is frequently characterized by cholangiocellular differentiation. The site specific antibody ATZ11 is a reliable morphologic tool for detecting PiZ individuals.

Detection of alpha-1-antitrypsin PiZ individuals by SSCP and DNA sequencing in formalin-fixed and paraffin-embedded tissue: a comparison with immunohistochemical analysis

BACKGROUND/AIM

The role of alpha-1-antitrypsin (AAT) deficiency in the development of cirrhosis and carcinoma of the liver can be investigated from the analysis of archival biopsy specimens. Immunohistochemistry can visualize the storage of defective protease inhibitor (Pi) variant Z, but does not allow differentation between homozygous and heterozygous patients. The aim of the study was to establish a method for the detection of the PiZ mutation on the gene level.

METHODS

Liver biopsy and autopsy samples in which AAT deficiency was detected immunohistochemically by a monoclonal PiZ-antibody were analyzed by single-strand conformational polymorphism (SSCP) to reliably determine hetero- and homozygote carrier state in the absence of blood samples and to confirm the histological diagnosis. The accuracy of SSCP was verified by direct DNA sequencing.

RESULTS

Tissue slices (>0.8 cm2) from 29 consecutive cases with immunohistochemically detected PiZ depositions and from ten PiZ-negative control cases were provided for extraction and amplification of DNA. In comparison to wild-type sequence of AAT exon V, all 29 cases showed band shifts on SSCP analysis, with a heterozygous pattern in 28 patients and a homozygous pattern in one patient. DNA sequence analysis revealed the same single-base mutation at position 342 of AAT exon V.

CONCLUSIONS

SSCP analysis proved a sensitive and specific technique for the detection of the PiZ mutation at the gene level, which allowed unequivocal differentiation between heterozygous and homozygous PiZ status from paraffin-embedded archival tissue specimens. Besides a use in diagnostic pathology, this technique could be valuable for prenatal diagnosis and population screening purposes.