Homozygous PiZZ alpha-1 antitrypsin deficiency (α1ATD) is a well-known cause of liver disease (LD) in children and adults (1). However, the role of the heterozygous PiZ state of α1ATD in the pathogenesis of chronic LD is still a matter of controversy (2-4). Although initial reports found no association between the PiZ carrier state and LD (2,4,5), recent studies have suggested that the presence of PiZ may explain some cases of LD of unknown etiology including cryptogenic cirrhosis (6-12). Unfortunately, most of these studies were conducted before the discovery of the hepatitis C virus (HCV) and before the association between nonalcoholic fatty liver disease (NAFLD) and cryptogenic cirrhosis was established. A few later studies have suggested that PiZ heterozygous state may be associated with increased severity and worse outcome in LD of known etiologies, such as HCV, alcoholic liver disease (ALD) or NAFLD (6-9). Similar relationship has been described in several studies for the PiZ heterozygous state of α1ATD and lung disease (13-17). The aims of our study were (1) to establish the frequency of the PiZ carrier state among patients with chronic LD, seen at the outpatient Liver Clinics of the University of Miami (2); determine the prevalence of the PiMZ phenotype among liver patients of ethnic groups other than White (3); Establish the prevalence of the PiZ carrier state in LD of various etiologies (i.e., chronic hepatitis C, ALD, NAFLD, etc.) compared with patients with no LD in a large US population and (4) determine whether the prevalence of PiZ is increased in patients with more severe LD due to any etiology. We hypothesized that the finding of a greater prevalence of PiMZ heterozygotes in patients with more advanced LD due to another etiology would suggest an interaction between the 2 conditions, resulting in an increased probability of developing end-stage LD in affected individuals. This article presents interim results pertaining to this ongoing study.
Patients and Diagnostic Testing
We conducted a cross sectional case-control study among patients with well-established LD attending the Liver Clinics at the University of Miami and Jackson Memorial Hospital. The presented analysis consists of the data collected from April 2002 through April 2004. For a control group, we enrolled subjects with no history of LD and no clinical or laboratory evidence of LD, attending the outpatient Medicine Clinics of the University of Miami and Jackson Memorial Hospital. Medical records of all subjects were evaluated for medical history, history of alcohol drinking, hepatic biochemical tests and etiology of LD including serological tests for hepatitis B and C (HBsAg, anti HBs, anti HBc, HBV DNA by Polymerase Chain Reaction [PCR], anti HCV and HCV RNA by PCR), autoimmune LD (anti nuclear antibodies, anti smooth muscle antibodies, anti mitochondrial and anti M-2 antibodies) serum iron, iron-binding capacity and ferritin levels. Liver biopsy results were obtained and recorded.
Decompensated LD was defined as Child-Pugh score of ≥7 based on the presence of ascites, hepatic encephalopathy, serum bilirubin level>2.0 mg/dL, prothrombin time ≥4 seconds above control value and serum albumin <3.5.
Nonalcoholic fatty liver disease was diagnosed when typical histological findings including steatosis, ballooning, inflammation and fibrosis were present in the absence of any other etiology.
Cirrhosis was diagnosed as due to NAFLD in any one of 2 conditions: (1) histological evaluation showed typical findings for NAFLD in the absence of other etiology and (2) the patients had 2 or more of the components of the metabolic syndrome (diabetes mellitus, hyperlipidemia, hypertension and obesity) in the absence of other etiology. The diagnosis of cryptogenic cirrhosis was made when complete evaluation failed to reveal a clear etiology and there were less than 2 components of the metabolic syndrome. The severity of LD was determined by clinical evaluation, lab tests, imaging studies and histopathology.
All blood samples for α1AT were separated into serum and leukocyte samples and tested for α1AT levels and α1AT phenotype respectively. Determination of α1AT phenotype and concentration were performed as previously describe (18-20). The genotyping of samples for the α1AT S and Z alleles was done using a combination of PCR amplification and restriction enzyme digestion followed by agarose gel electrophoresis. This approach is based on PCR amplification of DNA around the S and Z mutation using genomic DNA as template and unique (mutagenic) forward primers designed to create a Taq I restriction enzyme site (TCGA) on amplification of normal allele only. The 51 flanking sequence of wild type and mutated α1AT and that of the forward primers is shown below:
Lower case indicates mutated base and underscore indicates nucleotide different in the primer from the wild type sequence.
Extension of the forward primer during PCR, thus, allows the creation of a Taq I site (TCGA) in the wild type allele only. This facilitates the detection of the 2 alleles on separation of DNA bands on agarose gel after Taq I digestion of amplified DNA.
This protocol was approved by the institutional review board of the University of Miami, and informed consent was obtained from all the participants.
The prevalence of the PiMZ α1AT phenotype in our general LD group was compared with the control group using the χ2 test. The distribution of PiMZ among patients with less or more advanced LD in the various disease subgroups, was analyzed and compared using Fisher exact test.
Out of a projected population of 2500 patients, a total of 1405 were enrolled from April 2002 through April 2004 and were included in this interim analysis. Six-hundred-fifty-one subjects had a well-established LD, whereas 754 had no evidence for LD on a clinical and biochemical evaluation. One hundred seventy-three patients had decompensated cirrhosis requiring liver transplantation. Demographic and clinical data of our subject population is presented in Table 1.
Hepatitis C virus related LD was the most prevalent in our LD group, followed by NAFLD, ALD and cryptogenic LD. Other diseases included hepatitis B virus-related LD, autoimmune hepatitis, primary biliary cirrhosis and primary sclerosing cholangitis.
Of our entire subject population only 1 was found to have homozygous PiZZ phenotype. This patient had Child B cirrhosis and HCV infection. Before his enrollment he was diagnosed as having HCV-related cirrhosis and was listed for liver transplantation.
PiMM was the predominant phenotype accounting for 90.3% of the total population. The overall prevalence of all heterozygous states in our subject population was 9.7% (136/1405). This prevalence was almost identical in subjects with or without LD (9.5%, 62/651 in subjects with LD and 9.8%, 74/754 in subjects without LD). The phenotype distribution in the 2 populations is presented in Table 2. The heterozygous phenotype PiMS was the most prevalent in all groups (7.5% in the general population). PiMZ was significantly more prevalent in White patients compared to Hispanics (3.5% vs. 1.7%; P = 0.029). In contrast, PiMS was significantly more prevalent in the Hispanic compared with the White population (9% vs. 4.4%; P = 0.018).
There was no difference in PiMZ prevalence between the total LD group and the group with no LD (2.1% vs. 1.7%; P = 0.64) (Fig. 1). Within the LD group, 5.7% of 173 patients with decompensated LD, listed for liver transplant, had PiMZ, compared with 2.1% of 478 patients with less severe LD (P = 0.016) (Fig. 2). Similarly, there was a disproportionately higher prevalence of PiZ among HCV patients (5.6%) and NAFLD patients (5%) with decompensated LD, compared with HCV patients (1.2%) and NAFLD patients (1.9%) with less severe LD (P = 0.017 and 0.044, respectively). Patients with cryptogenic cirrhosis, who did not have features of NAFLD, did not have a higher prevalence of PiMZ compared with patients with LD of known etiologies (1.9% vs. 2.3%; P = 0.12) (Fig. 2).
To determine whether the presence of PiMZ was associated with progression to advanced LD at an earlier age, statistical comparisons of the mean age of patients with advanced LD were made between PiMZ heterozygotes and PiMM phenotypes within disease subgroups. No statistically significant differences were found.
No significant differences were found in serum levels of α1AT between patients with or without LD, or between patients with the PiMZ or the PiMM phenotypes.
Homozygous PiZZ α1ATD is one of the most common inherited metabolic disorders and the most common genetic cause of LD in children. Its incidence ranges from 1 in 6000 to 1200 live births. (1) The prevalence of the heterozygous states of α1ATD in the United States ranges from 6 to 12% (21). The prevalence of the heterozygous PiZ state ranges from 2% to 4% in different populations and is highest in individuals of Northern and Western European descent (21,22). The most common heterozygous phenotype is the PiMS, which constitutes about 70% of the heterozygote group, whereas the PiMZ phenotype constitutes about 28% and the SZ about 1% (21).
In our total population, 9.7% of the subjects had heterozygous phenotypes with predominance of the PiMS phenotype (7.5%) and a minority of PiMZ phenotype (1.9%) (Table 2). In agreement with previous reports (21), our Hispanic population showed a significantly lower prevalence of the PiMZ phenotype compared with the White population (1.7% vs. 3.5%) and a significantly higher prevalence of the PiMS phenotype (9% vs. 4.4%).
The association between LD and the homozygous PiZZ state has been well established in neonates, children and adults (1); however, the role of the PiZ heterozygous state as a possible cause of LD is still debated.
Initial studies found no association between the heterozygous α1AT phenotypes and LDs (2-5). However, several later studies have suggested that such association may in fact exist (6-12). In one of the pivotal studies Hodges et al. (9) showed that the PiMZ phenotype was significantly more prevalent in patients with cirrhosis (9.2%) compared with a general group of patients with LD (2.4%). These differences increased when patients with cirrhosis were compared with LDs with no cirrhosis such as acute hepatitis, cholestasis, fatty infiltration and non specific changes. A subgroup analysis revealed that patients with cryptogenic cirrhosis and those with "non-B chronic hepatitis" had a significantly higher prevalence of the PiMZ phenotype (21%) compared with the groups of alcoholic cirrhosis and cirrhosis from other causes (2.6%). Unfortunately, these results were obtained before the discovery of the HCV, and before NAFLD was clearly defined, which hampered the subanalysis of these groups. In a more recent study Eigenbrodt et al. (6) retrospectively examined the prevalence of abnormal α1AT phenotypes in 683 adult White patients with end stage LD, who were listed for liver transplantation. The PiMZ prevalence in these patients was significantly higher compared with a historical control group of 904 White Minnesota blood donors (7.3% vs. 2.8%). When compared with the control population, the odds ratio of having a heterozygous PiZ phenotype was significantly higher in White patients with hepatitis C, ALD, hepatocellular carcinoma and cryptogenic cirrhosis (6). Similar finding were reported by Graziadei et al. (8) in 599 adults with end-stage LD showing significantly higher PiMZ prevalence compared to the historical controls (8.2% vs. 2-4%). When broken down according to specific etiologies of LD, PiMZ was found in higher prevalence in patients with cryptogenic cirrhosis, compared with LDs of known etiologies, such as alcoholic, autoimmune and cholestatic LD (8). These data suggest that individuals carrying a single PiZ allele for α1AT may be at increased risk of developing cirrhosis and liver failure, even in the absence of identifiable coexistent LD. Similar findings were demonstrated from a different perspective by Fischer et al. (7) who compared the prevalence of immunohistochemically detectable PiZ phenotype in consecutive liver biopsies from patients with or without LDs. They found that in liver biopsies from PiZ heterozygous patients, the extent of PiZ deposits correlated well with the inflammatory activity and stage of fibrosis, and cirrhotic livers contained globular PiZ deposits significantly more often than biopsies with minor fibrosis. They concluded that the PiZ carrier state can aggravate liver damage in coexistent chronic LDs (7).
Our report presents interim results of one of the largest case-control studies exploring the role of the PiZ carrier state in LD. It shows no significant difference in the prevalence of PiZ between the general groups of patients with or without LD, which suggests that the PiMZ heterozygous state does not play a roll as a cause of de-novo LD. Furthermore, in contrast to a few previous reports, the prevalence of PiZ was not increased in patients with cryptogenic cirrhosis compared with patients with no LD or to those with LD of known etiologies. In contrast PiMZ was significantly more prevalent in patients with advanced LD versus those with less advanced disease. Specifically, patients with advanced disease due to HCV and NAFLD had a significantly higher prevalence of PiMZ compared with HCV and NAFLD patients with less-advanced disease. The discrepancy between our results and those of previous reports in patients with cryptogenic cirrhosis may be attributed in part to the inclusion of NAFLD patients in the so-called "cryptogenic cirrhosis" groups and to the relatively low number of "pure" non-NAFLD cryptogenic cirrhosis patients in our study.
These interim results suggest that the PiMZ α1ATD heterozygous state may have a role in worsening LD due to HCV or NAFLD, and may explain in part a more rapid progression and worse outcome in certain patients with HCV or NAFLD.
Comparable relationships have been found between the PiMZ heterozygous state and lung disease. With the exception of a few reports (23), most studies have shown similar pulmonary function (FEV1 values) between PiMM and PiMZ patients (13-17). However, when an additional insult, such as smoking, was introduced, MZ patients tended to do worse compared with MM patients (24,25). Klayton et al. (24) found that elderly heterozygotes who smoked had a significantly higher incidence of chronic obstructive pulmonary disease (COPD) compared with normal homozygotes (PiMM) who smoked. In contrast, they found no difference in the incidence of COPD between subjects with MM and MZ phenotypes who did not smoke. Similarly, Sandford et al. (25) found that the MZ phenotype was significantly more prevalent in smokers with COPD than in those without obstructive lung disease. Other researchers showed that smokers with the MZ carrier state had a greater annual decline in FEV-1 and a higher risk of COPD, compared with the general population (21).
Similar to previous studies, our study illustrates the existing problems concerning the diagnosis of the heterozygous PiZ states of α1ATD. It is easily overlooked by clinical exploration, laboratory tests and routinely stained liver biopsies. Heterozygotes with LD may have normal serum levels of α1AT and may be missed even when periodic acid-S staining is applied because the typical histologic features can be subtle.
In conclusion, we found no association between the heterozygous PiZ state of α1ATD and the presence of chronic LD in general, or the presence of cryptogenic cirrhosis. In contrast, patients with decompensated LD of any etiology had a significantly higher prevalence of PiMZ compare with patients with compensated LD. Furthermore, in patients with chronic LD due to HCV or NAFLD there was a significant association between the PiMZ heterozygous state and increased severity of LD and the need for liver transplantation. These interim results suggest that the PiMZ α1ATD heterozygous state may have a role in worsening LD due to HCV or NAFLD. Larger subject numbers are necessary to establish whether similar disease modifier association exists for other LDs.
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