The selective advantage of alpha1-antitrypsin deficiency

Pulmonary manifestations of alpha 1 antitrypsin deficiency

Alpha 1 antitrypsin deficiency is a widely under recognized autosomal codominant condition caused by genetic mutations in the SERPINA 1 gene, which encodes for alpha 1 antitrypsin (AAT), a serine protease inhibitor. The SERPINA 1 gene contains 120 variants and mutations in the gene may decrease AAT protein levels or result in dysfunctional proteins. This deficiency leads to unopposed protease activity in tissues, thereby promoting pulmonary and hepatic disease. The most common genotype associated with pulmonary disease is the ZZ genotype, and the most frequent pulmonary manifestation is emphysema. Although its pathophysiology may differ from cigarette smoking related chronic obstructive pulmonary disease, smoking itself can hasten lung decline in alpha 1 antitrypsin deficiency (AATD). The diagnosis of AATD is made through AAT protein testing along with genotyping. AATD patients with obstructive airflow limitation may qualify for intravenous augmentation with AAT. However, there is ongoing research to allow for earlier detection and treatment. This review describes in general terms the genetic mechanisms of AATD; its pathogenesis and the impact of cigarette smoke; and its clinical manifestations, diagnosis, treatment, and prognosis. We hope to stimulate research in the field, but mostly we wish to enhance awareness to promote early diagnosis and treatment in those eligible for intervention.

Alpha-1 antitrypsin inhibits fractalkine-mediated monocyte-lung endothelial cell interactions

Chronic obstructive pulmonary disease (COPD) is characterized by nonresolving inflammation fueled by breach in the endothelial barrier and leukocyte recruitment into the airspaces. Among the ligand-receptor axes that control leukocyte recruitment, the full-length fractalkine ligand (CX3CL1)-receptor (CX3CR1) ensures homeostatic endothelial-leukocyte interactions. Cigarette smoke (CS) exposure and respiratory pathogens increase expression of endothelial sheddases, such as a-disintegrin-and-metalloproteinase-domain 17 (ADAM17, TACE), inhibited by the anti-protease α-1 antitrypsin (AAT). In the systemic endothelium, TACE cleaves CX3CL1 to release soluble CX3CL1 (sCX3CL1). During CS exposure, it is not known whether AAT inhibits sCX3CL1 shedding and CX3CR1+ leukocyte transendothelial migration across lung microvasculature. We investigated the mechanism of sCX3CL1 shedding, its role in endothelial-monocyte interactions, and AAT effect on these interactions during acute inflammation. We used two, CS and lipopolysaccharide (LPS) models of acute inflammation in transgenic Cx3cr1gfp/gfp mice and primary human endothelial cells and monocytes to study sCX3CL1-mediated CX3CR1+ monocyte adhesion and migration. We measured sCX3CL1 levels in plasma and bronchoalveolar lavage (BALF) of individuals with COPD. Both sCX3CL1 shedding and CX3CR1+ monocytes transendothelial migration were triggered by LPS and CS exposure in mice, and were significantly attenuated by AAT. The inhibition of monocyte-endothelial adhesion and migration by AAT was TACE-dependent. Compared with healthy controls, sCX3CL1 levels were increased in plasma and BALF of individuals with COPD, and were associated with clinical parameters of emphysema. Our results indicate that inhibition of sCX3CL1 as well as AAT augmentation may be effective approaches to decrease excessive monocyte lung recruitment during acute and chronic inflammatory states.NEW & NOTEWORTHY Our novel findings that AAT and other inhibitors of TACE, the sheddase that controls full-length fractalkine (CX3CL1) endothelial expression, may provide fine-tuning of the CX3CL1-CX3CR1 axis specifically involved in endothelial-monocyte cross talk and leukocyte recruitment to the alveolar space, suggests that AAT and inhibitors of sCX3CL1 signaling may be harnessed to reduce lung inflammation.

Thrombotic risk determined by rare and common SERPINA1 variants in a population-based cohort study

BACKGROUND

Severe alpha-1-antitrypsin deficiency (AATD), phenotype PiZZ, was associated with venous thromboembolism (VTE) in a case-control study.

OBJECTIVES

This study aimed to determine the genetic variation in the SERPINA1 gene and a possible thrombotic risk of these variants in a population-based cohort study.

PATIENTS/METHODS

The coding sequence of SERPINA1 was analyzed for the Z (rs28929474), S (rs17580), and other qualifying variants in 28,794 subjects without previous VTE (born 1923-1950, 60% women), who participated in the Malmö Diet and Cancer study (1991-1996). Individuals were followed from baseline until the first event of VTE, death, or 2018.

RESULTS

Resequencing the coding sequence of SERPINA1 identified 84 variants in the total study population, 21 synonymous, 62 missense, and 1 loss-of-function variant. Kaplan-Meier analysis showed that homozygosity for the Z allele increased the risk of VTE whereas heterozygosity showed no effect. The S (rs17580) variant was not associated with VTE. Thirty-one rare variants were qualifying and included in collapsing analysis using the following selection criteria, loss of function, in frame deletion or non-benign (PolyPhen-2) missense variants with minor allele frequency (MAF) <0.1%. Combining the rare qualifying variants with the Z variant showed that carrying two alleles (ZZ or compound heterozygotes) showed increased risk. Cox regression analysis revealed an adjusted hazard ratio of 4.5 (95% confidence interval 2.0-10.0) for combinations of the Z variant and rare qualifying variants. One other variant (rs141620200; MAF = 0.002) showed an increased risk of VTE.

CONCLUSIONS

The SERPINA1 ZZ genotype and compound heterozygotes for severe AATD are rare but associated with VTE in a population-based Swedish study.

Alpha-1 Antitrypsin and Hepatocellular Carcinoma in Liver Cirrhosis: SERPINA1 MZ or MS Genotype Carriage Decreases the Risk

Heterozygotes for Z or S alleles of alpha-1-antrypsin (AAT) have low serum AAT levels. Our aim was to compare the risk of hepatocellular carcinoma (HCC) in patients with liver cirrhosis carrying the SERPINA1 MM, MZ and MS genotypes. The study groups consisted of 1119 patients with liver cirrhosis of various aetiologies, and 3240 healthy individuals served as population controls. The MZ genotype was significantly more frequent in the study group (55/1119 vs. 87/3240, p < 0.0001). The MS genotype frequency was comparable in controls (32/119 vs. 101/3240, p = 0.84). MZ and MS heterozygotes had lower serum AAT level than MM homozygotes (medians: 0.90 g/L; 1.40 g/L and 1.67 g/L; p < 0.001 for both). There were significantly fewer patients with HCC in the cirrhosis group among MZ and MS heterozygotes than in MM homozygotes (5/55 and 1/32 respectively, vs. 243/1022, p < 0.01 for both). The risk of HCC was lower in MZ and MS heterozygotes than in MM homozygotes (OR 0.3202; 95% CI 0.1361–0.7719 and OR 0.1522; 95% CI 0.02941–0.7882, respectively). Multivariate analysis of HCC risk factors identified MZ or MS genotype carriage as a protective factor, whereas age, male sex, BMI and viral aetiology of cirrhosis increased HCC risk.

Severe alpha-1-antitrypsin deficiency increases the risk of venous thromboembolism

BACKGROUND

Severe alpha-1-antitrypsin deficiency (AATD), phenotype PiZZ, is associated with increased risk of liver disease and chronic obstructive pulmonary disease (COPD), but the risk of venous thromboembolism (VTE) is unknown. Our aim was to evaluate the risk of VTE in individuals with severe AATD compared with control subjects from the general population.

METHODS

Individuals with severe AATD (n = 1577) were recruited from the Swedish national AATD register. Control subjects (n = 5969) were selected from the OLIN (Obstructive Lung Disease in Northern Sweden) studies, that include a random general population sample. Longitudinal data on VTE and diagnoses were obtained from the Swedish National Patient Registry. Associations were analyzed using multivariable Cox regression.

RESULTS

At inclusion, 46% of the AATD individuals and 53% of the controls were never-smokers. COPD was present in 46% of the AATD individuals compared with 4% of the controls. During a median follow-up of 18 years, 116 (7%) of the AATD individuals and 89 (1%) of the control subjects developed VTE, unadjusted hazard ratio 6.5 (95% confidence interval 4.9-8.6). Risk factors for incident VTE were male gender, age, COPD, cancer, and liver disease. Adjusting for these factors, the AATD individuals had a significantly higher risk of incident VTE, adjusted hazard ratio 4.2 (95% confidence interval 2.9-6.2) as compared with the controls.

CONCLUSION

Subjects with severe AATD have considerably increased risk of developing VTE compared with the general population, even after accounting for risk factors. This calls for optimized risk factor management and clinical follow-up of this patient group.

Hepatic and Extrahepatic Sources and Manifestations in Endoplasmic Reticulum Storage Diseases

Alpha-1-antitrypsin (AAT) and fibrinogen are secretory acute phase reactant proteins. Circulating AAT and fibrinogen are synthesized exclusively in the liver. Mutations in the encoding genes result in conformational abnormalities of the two molecules that aggregate within the rough endoplasmic reticulum (RER) instead of being regularly exported. That results in AAT-deficiency (AATD) and in hereditary hypofibrinogenemia with hepatic storage (HHHS). The association of plasma deficiency and liver storage identifies a new group of pathologies: endoplasmic reticulum storage disease (ERSD).

Pleiotropic associations of heterozygosity for the SERPINA1 Z allele in the UK Biobank

Homozygosity for the SERPINA1 Z allele causes α1-antitrypsin deficiency, a rare condition that can cause lung and liver disease. However, the effects of Z allele heterozygosity on nonrespiratory phenotypes, and on lung function in the general population, remain unclear. We conducted a large, population-based study to determine Z allele effects on >2400 phenotypes in the UK Biobank (N=303 353). Z allele heterozygosity was strongly associated with increased height (β=1.02 cm, p=3.91×10-68), and with other nonrespiratory phenotypes including increased risk of gall bladder disease, reduced risk of heart disease and lower blood pressure, reduced risk of osteoarthritis and reduced bone mineral density, increased risk of headache and enlarged prostate, as well as with blood biomarkers of liver function. Heterozygosity was associated with higher height-adjusted forced expiratory volume in 1 s (FEV1) (β=19.36 mL, p=9.21×10-4) and FEV1/forced vital capacity (β=0.0031, p=1.22×10-5) in nonsmokers, whereas in smokers, this protective effect was abolished. Furthermore, we show for the first time that sex modifies the association of the Z allele on lung function. We conclude that Z allele heterozygosity and homozygosity exhibit opposing effects on lung function in the UK population, and that these associations are modified by smoking and sex. In exploratory analyses, heterozygosity for the Z allele also showed pleiotropic associations with nonrespiratory health-related traits and disease risk.

Alpha-1 antitrypsin (AAT) augmentation therapy in individuals with the PI*MZ genotype: a pro/con debate on a working hypothesis

Alpha-1 antitrypsin deficiency (AATD) is a significantly under-diagnosed genetic condition caused by reduced levels and/or functionality of alpha-1 antitrypsin (AAT), predisposing individuals to lung, liver or other systemic diseases. The management of individuals with the PI*MZ genotype, characterized by mild or moderate AAT deficiency, is less clear than of those with the most common severe deficiency genotype (PI*ZZ). Recent genetic data suggest that the PI*MZ genotype may be significantly more prevalent than currently thought. The only specific treatment for lung disease associated with severe AATD is the intravenous infusion of AAT augmentation therapy, which has been shown to slow disease progression in PI*ZZ individuals. There is no specific evidence for the clinical benefit of AAT therapy in PI*MZ individuals, and the risk of emphysema development in this group remains controversial. As such, current guidelines do not support the use of AAT augmentation in PI*MZ individuals. Here, we discuss the limited data on the PI*MZ genotype and offer pro and con perspectives on pursuing an AAT-specific therapeutic strategy in PI*MZ individuals with lung disease. Ultimately, further research to demonstrate the safety, risk/benefit balance and efficacy of AAT therapy in PI*MZ individuals is needed.

Known Mutations at the Cause of Alpha-1 Antitrypsin Deficiency an Updated Overview of SERPINA1 Variation Spectrum

Alpha-1-Antitrypsin deficiency (AATD), caused by SERPINA1 mutations, is one of the most prevalent Mendelian disorders among individuals of European descend. However, this condition, which is characterized by reduced serum levels of alpha-1-antitrypsin (AAT) and associated with increased risks of pulmonary emphysema and liver disease in both children and adults, remains frequently underdiagnosed. AATD clinical manifestations are often correlated with two pathogenic variants, the Z allele (p.Glu342Lys) and the S allele (p.Glu264Val), which can be combined in severe ZZ or moderate SZ risk genotypes. Yet, screenings of AATD cases and large sequencing efforts carried out in both control and disease populations are disclosing outstanding numbers of rare SERPINA1 variants (>500), including many pathogenic and other likely deleterious mutations. Generally speaking, pathogenic variants can be subdivided into either loss- or gain-of-function according to their pathophysiological effects. In AATD, the loss-of-function is correlated with an uncontrolled activity of elastase by its natural inhibitor, the AAT. This phenomenon can result from the absence of circulating AAT (null alleles), poor AAT secretion from hepatocytes (deficiency alleles) or even from a modified inhibitory activity (dysfunctional alleles). On the other hand, the gain-of-function is connected with the formation of AAT polymers and their switching on of cellular stress and inflammatory responses (deficiency alleles). Less frequently, the gain-of-function is related to a modified protease affinity (dysfunctional alleles). Here, we revisit SERPINA1 mutation spectrum, its origins and population history with a greater emphasis on variants fitting the aforementioned processes of AATD pathogenesis. Those were selected based on their clinical significance and wider geographic distribution. Moreover, we also provide some directions for future studies of AATD clinically heterogeneity and comprehensive diagnosis.

Structural Characteristics in the γ Chain Variants Associated with Fibrinogen Storage Disease Suggest the Underlying Pathogenic Mechanism

Particular fibrinogen γ chain mutations occurring in the γ-module induce changes that hamper γ-γ dimerization and provoke intracellular aggregation of the mutant fibrinogen, defective export and plasma deficiency. The hepatic storage predisposes to the development of liver disease. This condition has been termed hereditary hypofibrinogenemia with hepatic storage (HHHS). So far, seven of such mutations in the fibrinogen γ chain have been detected. We are reporting on an additional mutation occurring in a 3.5-year-old Turkish child undergoing a needle liver biopsy because of the concomitance of transaminase elevation of unknown origin and low plasma fibrinogen level. The liver biopsy showed an intra-hepatocytic storage of fibrinogen. The molecular analysis of the three fibrinogen genes revealed a mutation (Fibrinogen Trabzon Thr371Ile) at exon 9 of the γ chain in the child and his father, while the mother and the brother were normal. Fibrinogen Trabzon represents a new fibrinogen γ chain mutation fulfilling the criteria for HHHS. Its occurrence in a Turkish child confirms that HHHS can present in early childhood and provides relevant epidemiological information on the worldwide distribution of the fibrinogen γ chain mutations causing this disease. By analyzing fibrinogen crystal structures and calculating the folding free energy change (ΔΔG) to infer how the variants can affect the conformation and function, we propose a mechanism for the intracellular aggregation of Fibrinogen Trabzon and other γ-module mutations causing HHHS.

Alpha-1 Antitrypsin Deficiency: a Rare Disease?

PURPOSE OF REVIEW

Commonly categorized as a rare disease, alpha-1 antitrypsin deficiency (AATD) is neither rare, when compared to many other genetic disorders, nor an actual disease, but rather a predisposition toward a wide variety of diseases. It is one of the most common genetic disorders which can lead to a spectrum of clinical manifestations, ranging from no symptoms to progressively debilitating systemic disease, most commonly affecting the lung and liver. It is therefore imperative for clinicians to recognize and be familiar with the spectrum of presentations, methods of diagnosis, and clinical management of AATD. It is also imperative for scientists to recognize the potential for progress in the management of this disorder.

RECENT FINDINGS

This review focuses on the current state of knowledge of AATD, including the wide range of presentations, diagnosis, and clinical management. In addition to the clinical implications of severe AATD, we discuss the relevance of heterozygous state with mild or moderate AATD in the development of both lung and liver disease. While our understanding of the multiple roles of alpha-1 antitrypsin (AAT) is on the rise, with appreciation of its immunomodulatory, anti-infective, and anti-inflammatory properties, this knowledge has yet to impact our ability to predict outcomes. We discuss nuances of augmentation therapy and review novel therapeutic approaches currently under investigation. With the expanding knowledge about the complexities of AAT function and its clinical relevance, and with the increasing ability to diagnose early and intervene on AATD, it should be our goal to change the perception of AATD as a correctable inherited disorder rather than a fatal disease.

Aggregation of M3 (E376D) variant of alpha1- antitrypsin

Alpha1-antitrypsin (α1AT) is an abundant serine-protease inhibitor in circulation. It has an important role in neutralizing the neutrophil elastase activity. Different pathogenic point mutations like Z(E342K)-α1AT have been implicated in the development of liver cirrhosis and Chronic Obstructive Pulmonary Disease (COPD), the latter being a cluster of progressive lung diseases including chronic bronchitis and emphysema. M3-α1AT (376Glu > Asp) is another variant of α1AT which so far is largely being considered as normal though increased frequency of the variant has been reported in many human diseases including COPD. We also observed increased frequency of M3-α1AT in COPD cases in Kashmiri population. The frequency of heterozygous (AC) genotype in cases and controls was 58.57% and 27.61% (odds-ratio 6.53 (2.27-15.21); p < 0.0001) respectively, while homozygous CC genotype was found to be 21.42% and 6.66% (odds-ratio 10.56 (3.63-18.64); p < 0.0001) respectively. Comparative in vitro investigations that include trypsin‒antitrypsin assay, Circular Dichroism spectroscopy and dynamic light scattering performed on wild-type (M-α1AT), M3-α1AT, and Z-α1AT proteins along with the molecular dynamics simulations revealed that M3-α1AT has properties similar to Z-α1AT capable of forming aggregates of varied size. Our maiden observations suggest that M3-α1AT may contribute to the pathogenesis of COPD and other disorders by mechanisms that warrant further investigations.

Protein modeling to assess the pathogenicity of rare variants of SERPINA1 in patients suspected of having Alpha 1 Antitrypsin Deficiency

Background

Alpha 1 Antitrypsin (AAT) is a key serum proteinase inhibitor encoded by SERPINA1. Sequence variants of the gene can cause Alpha 1 Antitrypsin Deficiency (AATD), a condition associated with lung and liver disease. The majority of AATD cases are caused by the ‘Z’ and ‘S’ variants – single-nucleotide variations (SNVs) that result in amino acid substitutions of E342K and E264V. However, SERPINA1 is highly polymorphic, with numerous potentially clinically relevant variants reported. Novel variants continue to be discovered, and without reports of pathogenicity, it can be difficult for clinicians to determine the best course of treatment.

Methods

We assessed the utility of next-generation sequencing (NGS) and predictive computational analysis to guide the diagnosis of patients suspected of having AATD. Blood samples on serum separator cards were submitted to the DNA₁ Advanced Screening Program (Biocerna LLC, Fulton, Maryland, USA) by physicians whose patients were suspected of having AATD. Laboratory analyses included quantification of serum AAT levels, qualitative analysis by isoelectric focusing, and targeted genotyping and NGS of the SERPINA1 gene. Molecular modeling software UCSF Chimera (University College of San Francisco, CA) was used to visualize the positions of amino acid changes as a result of rare/novel SNVs. Predictive software was used to assess the potential pathogenicity of these variants; methods included a support vector machine (SVM) program, PolyPhen-2 (Harvard University, Cambridge, MA), and FoldX (Centre for Genomic Regulation, Barcelona, Spain).

Results

Samples from 23 patients were analyzed; 21 rare/novel sequence variants were identified by NGS, including splice variants (n = 2), base pair deletions (n = 1), stop codon insertions (n = 2), and SNVs (n = 16). Computational modeling of protein structures caused by the novel SNVs showed that 8 were probably deleterious, and two were possibly deleterious. For the majority of probably/possibly deleterious SNVs (I50N, P289S, M385T, M221T, D341V, V210E, P369H, V333M and A142D), the mechanism is probably via disruption of the packed hydrophobic core of AAT. Several deleterious variants occurred in combination with more common deficiency alleles, resulting in very low AAT levels.

Conclusions

NGS and computational modeling are useful tools that can facilitate earlier, more precise diagnosis, and consideration for AAT therapy in AATD.

Electronic supplementary material

The online version of this article (10.1186/s12881-019-0852-5) contains supplementary material, which is available to authorized users.

Cardiovascular risk in patients with alpha-1-antitrypsin deficiency

Background

Alpha-1-antitrypsin deficiency (AATD) is a rare inherited condition caused by mutations of the SERPINA1 gene that is associated with the development of a COPD like lung disease. The comorbidities in patients with AATD-related lung diseases are not well defined. The aim of this study was to analyze the clinical phenotype of AATD patients within the German COPD cohort study COSYCONET (“COPD and SYstemic consequences-COmorbidities NETwork”) cohort focusing on the distribution of comorbidities.

Method and results

The data from 2645 COSYCONET patients, including 139 AATD patients (110 with and 29 without augmentation therapy), were analyzed by descriptive statistics and regression analyses. We found significantly lower prevalence of cardiovascular comorbidities in AATD patients as compared to non-AATD COPD patients. After correction for age, pack years, body mass index, and sex, the differences were still significant for coronary artery disease (p = 0.002) and the prevalence of peripheral artery disease as determined by an ankle-brachial-index <= 0.9 (p = 0.035). Also the distribution of other comorbidities such as bronchiectasis differed between AATD and non-deficient COPD.

Conclusion

AATD is associated with a lower prevalence of cardiovascular disease, the underlying mechanisms need further investigation.

Electronic supplementary material

The online version of this article (10.1186/s12931-017-0655-1) contains supplementary material, which is available to authorized users.

Alpha-1-antitrypsin deficiency: Genetic variations, clinical manifestations and therapeutic interventions

Alpha-1-antitrypsin (AAT) is an acute phase secretory glycoprotein that inhibits neutrophil proteases like elastase and is considered as the archetype of a family of structurally related serine-protease inhibitors termed serpins. Serum AAT predominantly originates from liver and increases three to five fold during host response to tissue injury and inflammation. The AAT deficiency is unique among the protein-misfolding diseases in that it causes target organ injury by both loss-of-function and gain-of-toxic function mechanisms. Lack of its antiprotease activity is associated with premature development of pulmonary emphysema and loss-of-function due to accumulation of resultant aggregates in chronic obstructive pulmonary disease (COPD). This' in turn' markedly reduces the amount of AAT that is available to protect lungs against proteolytic attack by the enzyme neutrophil elastase. The coalescence of AAT deficiency, its reduced efficacy, and cigarette smoking or poor ventilation conditions have devastating effect on lung function. On the other hand, the accumulation of retained mutant proteins in the endoplasmic reticulum of hepatocytes in a polymerized form rather than secreted into the blood in its monomeric form is associated with chronic liver disease and predisposition to hepatocellular carcinoma (HCC) by gain- of- toxic function. Liver injury resulting from this gain-of-toxic function mechanism in which mutant AAT retained in the ER initiates a series of pathologic events, eventually culminating at liver cirrhosis and HCC. Here in this review, we underline the structural, genetic, polymorphic, biochemical and pathological advances made in the field of AAT deficiency and further comprehensively emphasize on the therapeutic interventions available for the patient.

The endoplasmic reticulum remains functionally connected by vesicular transport after its fragmentation in cells expressing Z-α1-antitrypsin

α1-Antitrypsin is a serine protease inhibitor produced in the liver that is responsible for the regulation of pulmonary inflammation. The commonest pathogenic gene mutation yields Z-α1-antitrypsin, which has a propensity to self-associate forming polymers that become trapped in inclusions of endoplasmic reticulum (ER). It is unclear whether these inclusions are connected to the main ER network in Z-α1-antitrypsin-expressing cells. Using live cell imaging, we found that despite inclusions containing an immobile matrix of polymeric α1-antitrypsin, small ER resident proteins can diffuse freely within them. Inclusions have many features to suggest they represent fragmented ER, and some are physically separated from the tubular ER network, yet we observed cargo to be transported between them in a cytosol-dependent fashion that is sensitive to N-ethylmaleimide and dependent on Sar1 and sec22B. We conclude that protein recycling occurs between ER inclusions despite their physical separation.-Dickens, J. A., Ordóñez, A., Chambers, J. E., Beckett, A. J., Patel, V., Malzer, E., Dominicus, C. S., Bradley, J., Peden, A. A., Prior, I. A., Lomas, D. A., Marciniak, S. J. The endoplasmic reticulum remains functionally connected by vesicular transport after its fragmentation in cells expressing Z-α1-antitrypsin.

Alpha-1 Antitrypsin and Lung Cell Apoptosis

Discovery of alpha-1 antitrypsin (A1AT) as the principal circulating inhibitor of neutrophil elastase was critical to the appreciation of protease/antiprotease imbalance involvement in the pathogenesis of emphysema. Additional targets of A1AT have been uncovered, along with their contribution to alveolar wall destruction induced by cigarette smoke exposure. We highlight in this report mechanisms of A1AT antiapoptotic effects on structural lung endothelial cells. This function was largely dependent on uptake of the protein from the circulation via clathrin- and, in part, caveolae-mediated endocytosis and on specific interactions with cysteine proteases such as capsase-3, -6, and -7. Exposures to cigarette smoke diminished A1AT intracellular uptake and its anticaspase action, suggesting that even in A1AT-suficient individuals, cigarette smoke may weaken the serpin's endothelial prosurvival effect. In addition, cigarette smoke exposure or genetic mutations known to induce posttranslational modifications such as oxidation or polymerization may alter A1AT bidirectional intracellular traffic in endothelial cells and thus determine its functional bioavailability in certain lung compartments. Uncovering and harnessing the A1AT canonical and noncanonical mechanisms will advance our understanding of the pathogenesis of emphysema and may provide means to improve the effectiveness of therapies in both A1AT-sufficient and A1AT-deficient individuals.

IgE-tailpiece associates with α-1-antitrypsin (A1AT) to protect IgE from proteolysis without compromising its ability to interact with FcεRI

Several splice variants of IgE exist in human plasma, including a variant called IgE-tailpiece (IgE-tp) that differs from classical IgE by the replacement of two carboxy-terminal amino acids with eight novel residues that include an ultimate cysteine. To date, the role of the secreted IgE-tp isoform in human immunity is unknown. We show that levels of IgE-tp are raised in helminth-infected donors, and that both the classical form of IgE (IgE-c) and IgE-tp interact with polymers of the serine protease inhibitor alpha-1-antitrypsin (A1AT). The association of IgE-tp with A1AT polymers in plasma protects the antibody from serine protease-mediated degradation, without affecting the functional interaction of IgE-tp with important receptors, including FcεR1. That polymers of A1AT protect IgE from degradation by helminth proteases may explain why these common and normally non-disease causing polymorphic variants of A1AT have been retained by natural selection. The observation that IgE can be complexed with polymeric forms of A1AT may therefore have important consequences for our understanding of the pathophysiology of pulmonary diseases that arise either as a consequence of A1AT-deficiency or through IgE-mediated type 1 hypersensitivity responses.

A study of common Mendelian disease carriers across ageing British cohorts: meta-analyses reveal heterozygosity for alpha 1-antitrypsin deficiency increases respiratory capacity and height

BACKGROUND

Several recessive Mendelian disorders are common in Europeans, including cystic fibrosis (CFTR), medium-chain-acyl-Co-A-dehydrogenase deficiency (ACADM), phenylketonuria (PAH) and alpha 1-antitrypsin deficiency (SERPINA1).

METHODS

In a multicohort study of >19,000 older individuals, we investigated the relevant phenotypes in heterozygotes for these genes: lung function (forced expiratory volume in 1 second (FEV1), forced vital capacity (FVC)) for CFTR and SERPINA1; cognitive measures for ACADM and PAH; and physical capability for ACADM, PAH and SERPINA1.

RESULTS

Findings were mostly negative but lung function in SERPINA1 (protease inhibitor (PI) Z allele, rs28929474) showed enhanced FEV1 and FVC (0.13 z-score increase in FEV1 (p=1.7 × 10(-5)) and 0.16 z-score increase in FVC (p=5.2 × 10(-8))) in PI-MZ individuals. Height adjustment (a known, strong correlate of FEV1 and FVC) revealed strong positive height associations of the Z allele (1.50 cm increase in height (p=3.6 × 10(-10))).

CONCLUSIONS

The PI-MZ rare (2%) SNP effect is nearly four times greater than the 'top' common height SNP in HMGA2. However, height only partially attenuates the SERPINA1-FEV1 or FVC association (around 50%) and vice versa. Height SNP variants have recently been shown to be positively selected collectively in North versus South Europeans, while the Z allele high frequency is localised to North Europe. Although PI-ZZ is clinically disadvantageous to lung function, PI-MZ increases both height and respiratory function; potentially a balanced polymorphism. Partial blockade of PI could conceivably form part of a future poly-therapeutic approach in very short children. The notion that elastase inhibition should benefit patients with chronic obstructive pulmonary disease may also merit re-evaluation. PI is already a therapeutic target: our findings invite a reconsideration of the optimum level in respiratory care and novel pathway potential for development of agents for the management of growth disorders.

Health-related quality of life in patients with alpha-1 antitrypsin deficiency: the French experience

The French registry of patients with alpha-1 antitrypsin deficiency (AATD)-associated emphysema was launched in 2006. Here, we aimed to report on the baseline characteristics of these patients, their health-related quality of life (HRQoL) and factors associated with HRQoL. Another goal was to survey the practices of French physicians regarding augmentation therapy. We included 273 patients with AATD, emphysema, obstructive-pattern [forced expiratory volume in 1 sec/forced volume capacity (FEV1/FVC) < 0.7], FEV1 ≤ 80% predicted. Mean (SD) age was 51.8 (11.1) years, 240 (87.9%) of patients were smokers or ex-smokers, mean (SD) FEV1 was 40.5% (15.7) predicted. Mean (SD) SGRQ score was 49.0 (20.0) and was higher for females than males (52.7 [20.7] vs 46.8 [18.2]; p = 0.01). Dyspnea showed the strongest association with SGRQ score (r = 0.65; p < 0.0001), followed by chronic bronchitis (r = 0.33; p < 0.0001) and wheezing (r = 0.32; p < 0.0001). Number of exacerbations in the year before inclusion was also significantly associated with SGRQ score (r = 0.36; p < 0.0001). The SGRQ score was associated with the 6-min walking distance (r = -0.53, p < 0.0001), FEV1 (% predicted, r = -0.53, p < 0.0001) and DLCO (% predicted, r = -0.52, p < 0.0001). It was also associated with the GOLD 2006 (r = 0.53; p < 0.0001) and GOLD 2011 (r = 0.63; p< 0.0001) classifications and with the BODE index (r = 0.37; p < 0.0001). Age, history of tobacco smoking or current smoking did not show any association with SGRQ total scores. On multivariate analysis, a model including age, chronic bronchitis, dyspnea (MRC scale), diffusing lung capacity and 6-min walking distance explained 57% of the variation in the score. The French registry provides important insights into the clinical characteristics of French patients with AATD-related emphysema.

[Alpha-1 antitrypsin deficiency: A model of alteration of protein homeostasis or proteostasis]

Chronic obstructive pulmonary disease (COPD) is currently the ninth leading cause of death in France and is predicted to become the third leading cause of worldwide morbidity and mortality by 2020. Risk factors for COPD include exposure to tobacco, dusts and chemicals, asthma and alpha-1 antitrypsin deficiency. This genetic disease, significantly under-diagnosed and under-recognized, affects 1 in 2500 live births and is an important cause of lung and, occasionally, liver disease. Alpha-1 antitrypsin deficiency is a pathology of proteostasis-mediated protein folding and trafficking pathways. To date, there are only palliative therapeutic approaches for the symptoms associated with this hereditary disorder. Therefore, a more detailed understanding is required of the folding and trafficking biology governing alpha-1 antitrypsin biogenesis and its response to drugs. Here, we review the cell biological, biochemical and biophysical properties of alpha-1 antitrypsin and its variants, and we suggest that alpha-1 antitrypsin deficiency is an example of cell autonomous and non-autonomous challenges to proteostasis. Finally, we review emerging strategies that may be used to enhance the proteostasis system and protect the lung from alpha-1 antitrypsin deficiency.

An evolutionary medicine approach to understanding factors that contribute to chronic obstructive pulmonary disease

Although many studies have been published on the causes and mechanisms of chronic obstructive pulmonary disease (COPD), the reason for the existence of COPD and the reasons why COPD develops in humans have hardly been studied. Evolutionary medical approaches are required to explain not only the proximate factors, such as the causes and mechanisms of a disease, but the ultimate (evolutionary) factors as well, such as why the disease is present and why the disease develops in humans. According to the concepts of evolutionary medicine, disease susceptibility is acquired as a result of natural selection during the evolutionary process of traits linked to the genes involved in disease susceptibility. In this paper, we discuss the following six reasons why COPD develops in humans based on current evolutionary medical theories: (1) evolutionary constraints; (2) mismatch between environmental changes and evolution; (3) co-evolution with pathogenic microorganisms; (4) life history trade-off; (5) defenses and their costs, and (6) reproductive success at the expense of health. Our perspective pursues evolutionary answers to the fundamental question, 'Why are humans susceptible to this common disease, COPD, despite their long evolutionary history?' We believe that the perspectives offered by evolutionary medicine are essential for researchers to better understand the significance of their work.

Functional analysis of novel alpha-1 antitrypsin variants G320R and V321F

Alpha-1 antitrypsin (AAT) gene is highly polymorphic, with a large number of rare variants whose phenotypic consequences often remain inconclusive. Studies addressing functional characteristics of AAT variants are of significant biomedical importance since deficiency and dysfunctionality of AAT are associated with liver and lung diseases. We report the results of the functional analysis of two naturally occurring AAT variants, G320R and V321F, previously identified in patients with lung disease. Neither of variants has been fully functionally characterized. In order to perform their functional analysis both variants were expressed in prokaryotic and eukaryotic systems and their intracellular localization, activity, stability, and polymerization were determined. The results of this study demonstrated that variants G320R and V321F have neither impaired activity against porcine pancreatic elastase nor propensity to form polymers. However, both variants had altered electrophoretic mobility and reduced thermostability when compared to M variant of the protein, indicating a slightly impaired secondary or tertiary structure.

Using antisense technology to develop a novel therapy for α-1 antitrypsin deficient (AATD) liver disease and to model AATD lung disease

Alpha-1 antitrypsin (AAT) is a serum protease inhibitor that belongs to the serpin superfamily. Mutations in AAT are associated with α-1 antitrypsin deficiency (AATD), a rare genetic disease with two distinct manifestations: AATD lung disease and AATD liver disease. AATD lung disease is caused by loss-of-function of AAT and can be treated with plasma-derived AAT. AATD liver disease is due to the aggregation and retention of mutant AAT protein in the liver; the only treatment available for AATD liver disease is liver transplantation. Here we demonstrate that antisense oligonucleotides (ASOs) targeting human AAT efficiently reduce levels of both short and long human AAT transcript in vitro and in transgenic mice, providing a novel therapy for AATD liver disease. In addition, ASO-mediated depletion of mouse AAT may offer a useful animal model for the investigation of AATD lung disease.

A novel method of detecting alpha-1 antitrypsin deficiency of Z mutant (GAG(342)AAG) in a single PCR reaction using base-quenched probe

BACKGROUND

Alpha-1 antitrypsin (A1AT) is a protease inhibitor that protects the tissues from degradation by neutrophil elastase under certain pathological process. Alpha-1 antitrypsin deficiency (A1ATD) could associate with both lung and liver pathogenicities. Of all the deficiency alleles, Z mutant is the most common variant and causes severe complications. Here, we described a novel and quick method to detect Z mutant using the base-quenched probe technique in only one single PCR reaction.

METHODS

Primers and probe were designed based on the base-quenched probe technique. Two vectors, representing the two genotypes, were constructed as amplification templates for validating the method. The Z mutant (GAG(342)AAG) was analyzed according to the melting curve. Finally, the accuracy was confirmed by direct sequencing.

RESULTS

Z mutant could be accurately distinguished from the wild type. The wild type resulted in high melting temperature (TM) (48.64±1.33°C), while when the Z mutation was present, the TM was shifted to an obvious low TM (41.38±0.9017°C). The sensitivity reached a low of 10(3) copies of template DNA with a clear melting valley and a complete concordance occurred between this method and the direct DNA sequencing.

CONCLUSION

The present described method is simple, quick and economic as well as suitable for large-scale genotyping studies and clinical testing of Z mutant in patients with emphysema and cirrhosis.

The molecular and cellular pathology of α₁-antitrypsin deficiency

Since its discovery 50 years ago, α₁-antitrypsin deficiency has represented a case study in molecular medicine, with careful clinical characterisation guiding genetic, biochemical, biophysical, structural, cellular, and in vivo studies. Here we highlight the milestones in understanding the disease mechanisms and show how they have spurred the development of novel therapeutic strategies. α₁-Antitrypsin deficiency is an archetypal conformational disease. Its pathogenesis demonstrates the interplay between protein folding and quality control mechanisms, with aberrant conformational changes causing liver and lung disease through combined loss- and toxic gain-of-function effects. Moreover, α₁-antitrypsin exemplifies the ability of diverse proteins to self-associate into a range of morphologically distinct polymers, suggesting a mechanism for protein and cell evolution.

Antisense oligonucleotide treatment ameliorates alpha-1 antitrypsin-related liver disease in mice

Alpha-1 antitrypsin deficiency (AATD) is a rare genetic disease that results from mutations in the alpha-1 antitrypsin (AAT) gene. The mutant AAT protein aggregates and accumulates in the liver leading to AATD liver disease, which is only treatable by liver transplant. The PiZ transgenic mouse strain expresses a human AAT (hAAT) transgene that contains the AATD-associated Glu342Lys mutation. PiZ mice exhibit many AATD symptoms, including AAT protein aggregates, increased hepatocyte death, and liver fibrosis. In the present study, we systemically treated PiZ mice with an antisense oligonucleotide targeted against hAAT (AAT-ASO) and found reductions in circulating levels of AAT and both soluble and aggregated AAT protein in the liver. Furthermore, AAT-ASO administration in these animals stopped liver disease progression after short-term treatment, reversed liver disease after long-term treatment, and prevented liver disease in young animals. Additionally, antisense oligonucleotide treatment markedly decreased liver fibrosis in this mouse model. Administration of AAT-ASO in nonhuman primates led to an approximately 80% reduction in levels of circulating normal AAT, demonstrating potential for this approach in higher species. Antisense oligonucleotides thus represent a promising therapy for AATD liver disease.

Deficiency of α-1-antitrypsin influences systemic iron homeostasis

There is evidence that proteases and antiproteases participate in the iron homeostasis of cells and living systems. We tested the postulate that α-1 antitrypsin (A1AT) polymorphism and the consequent deficiency of this antiprotease in humans are associated with a systemic disruption in iron homeostasis. Archived plasma samples from Alpha-1 Foundation (30 MM, 30 MZ, and 30 ZZ individuals) were analyzed for A1AT, ferritin, transferrin, and C-reactive protein (CRP). Plasma samples were also assayed for metals using inductively coupled plasma atomic emission spectroscopy (ICPAES). Plasma levels of A1AT in MZ and ZZ individuals were approximately 60% and 20% of those for MM individuals respectively. Plasma ferritin concentrations in those with the ZZ genotype were greater relative to those individuals with either MM or MZ genotype. Plasma transferrin for MM, MZ, and ZZ genotypes showed no significant differences. Linear regression analysis revealed a significant (negative) relationship between plasma concentrations of A1AT and ferritin while that between A1AT and transferrin levels was not significant. Plasma CRP concentrations were not significantly different between MM, MZ, and ZZ individuals. ICPAES measurement of metals confirmed elevated plasma concentrations of nonheme iron among ZZ individuals. Nonheme iron concentrations correlated (negatively) with levels of A1AT. A1AT deficiency is associated with evidence of a disruption in iron homeostasis with plasma ferritin and nonheme iron concentrations being elevated among those with the ZZ genotype.

In vivo selection of transplanted hepatocytes by pharmacological inhibition of fumarylacetoacetate hydrolase in wild-type mice

Genetic fumarylacetoacetate hydrolase (Fah) deficiency is unique in that healthy gene-corrected hepatocytes have a strong growth advantage and can repopulate the diseased liver. Unfortunately, similar positive selection of gene-corrected cells is absent in most inborn errors of liver metabolism and it is difficult to reach the cell replacement index required for therapeutic benefit. Therefore, methods to transiently create a growth advantage for genetically modified hepatocytes in any genetic background would be advantageous. To mimic the selective pressure of Fah deficiency in normal animals, an efficient in vivo small molecule inhibitor of FAH, 4-[(2-carboxyethyl)-hydroxyphosphinyl]-3-oxobutyrate (CEHPOBA) was developed. Microarray analysis demonstrated that pharmacological inhibition of FAH produced highly similar gene expression changes to genetic deficiency. As proof of principle, hepatocytes lacking homogentisic acid dioxygenase (Hgd) and hence resistant to FAH inhibition were transplanted into sex-mismatched wild-type recipients. Time course analyses of 4-6 weeks of CEHPOBA administration after transplantation showed a linear relationship between treatment length and replacement index. Compared to controls, recipients treated with the FAH-inhibitor had 20-100-fold increases in liver repopulation. We conclude that pharmacological inhibition of FAH is a promising approach to in vivo selection of hepatocytes.

Rare alpha-1-antitrypsin variants: are they really so rare?

Alpha-1-antitrypsin (α1-AT) deficiency is mainly evaluated in the diagnostic process of chronic obstructive pulmonary disease (COPD). Around 95% of individuals with severe α1-AT deficiency carry the PI*ZZ genotype. Little is known about the epidemiology of the remaining deficient α1-AT variants, which are called 'rare' due to their low prevalence. The retrospective revision of 3511 α1-AT deficiency determinations performed in Barcelona from 1998 to 2010 detected 1.6% of cases with rare α1-AT alleles, a rate similar to those reported in other European studies. Among these variants, PI*I and PI*Mmalton represented 54% of cases. Hence, the so-called 'rare' α1-AT alleles may not be rare as has been assumed. It would be of interest to implement simple allele-specific molecular biology methods to study the most prevalent rare variants in each region. Augmentation therapy is recommended in patients with emphysema and PI*ZZ genotype, but there is little evidence regarding the implications of rare variants on therapy.

The role of proteases, endoplasmic reticulum stress and SERPINA1 heterozygosity in lung disease and α-1 anti-trypsin deficiency

The serine proteinase inhibitor α-1 anti-trypsin (AAT) provides an antiprotease protective screen throughout the body. Mutations in the AAT gene (SERPINA1) that lead to deficiency in AAT are associated with chronic obstructive pulmonary diseases. The Z mutation encodes a misfolded variant of AAT that is not secreted effectively and accumulates intracellularly in the endoplasmic reticulum of hepatocytes and other AAT-producing cells. Until recently, it was thought that loss of antiprotease function was the major cause of ZAAT-related lung disease. However, the contribution of gain-of-function effects is now being recognized. Here we describe how both loss- and gain-of-function effects can contribute to ZAAT-related lung disease. In addition, we explore how SERPINA1 heterozygosity could contribute to smoking-induced chronic obstructive pulmonary diseases and consider the consequences.

A review of α1-antitrypsin deficiency

α(1)-Antitrypsin (AAT) deficiency is an underrecognized genetic condition that affects approximately 1 in 2,000 to 1 in 5,000 individuals and predisposes to liver disease and early-onset emphysema. AAT is mainly produced in the liver and functions to protect the lung against proteolytic damage (e.g., from neutrophil elastase). Among the approximately 120 variant alleles described to date, the Z allele is most commonly responsible for severe deficiency and disease. Z-type AAT molecules polymerize within the hepatocyte, precluding secretion into the blood and causing low serum AAT levels (∼ 3-7 μM with normal serum levels of 20-53 μM). A serum AAT level of 11 μM represents the protective threshold value below which the risk of emphysema is believed to increase. In addition to the usual treatments for emphysema, infusion of purified AAT from pooled human plasma-so-called "augmentation therapy"-represents a specific therapy for AAT deficiency and raises serum levels above the protective threshold. Although definitive evidence from randomized controlled trials of augmentation therapy is lacking and therapy is expensive, the available evidence suggests that this approach is safe and can slow the decline of lung function and emphysema progression. Promising novel therapies are under active investigation.

The prevalence of alpha-1 antitrypsin deficiency in Ireland

Background

Alpha-1 antitrypsin deficiency (AATD) results from mutations in the SERPINA1 gene and classically presents with early-onset emphysema and liver disease. The most common mutation presenting with clinical evidence is the Z mutation, while the S mutation is associated with a milder plasma deficiency. AATD is an under-diagnosed condition and the World Health Organisation recommends targeted detection programmes for AATD in patients with chronic obstructive pulmonary disease (COPD), non-responsive asthma, cryptogenic liver disease and first degree relatives of known AATD patients.

Methods

We present data from the first 3,000 individuals screened following ATS/ERS guidelines as part of the Irish National Targeted Detection Programme (INTDP). We also investigated a DNA collection of 1,100 individuals randomly sampled from the general population. Serum and DNA was collected from both groups and mutations in the SERPINA1 gene detected by phenotyping or genotyping.

Results

The Irish National Targeted Detection Programme identified 42 ZZ, 44 SZ, 14 SS, 430 MZ, 263 MS, 20 IX and 2 rare mutations. Analysis of 1,100 randomly selected individuals identified 113 MS, 46 MZ, 2 SS and 2 SZ genotypes.

Conclusion

Our findings demonstrate that AATD in Ireland is more prevalent than previously estimated with Z and S allele frequencies among the highest in the world. Furthermore, our targeted detection programme enriched the population of those carrying the Z but not the S allele, suggesting the Z allele is more important in the pathogenesis of those conditions targeted by the detection programme.

Proteostasis strategies for restoring alpha1-antitrypsin deficiency

The function of the human proteome is defined by the proteostasis network (PN) (Science 2008;319:916; Science 2010;329:766), a biological system that generates, protects, and, where necessary, degrades a protein to optimize the cell, tissue, and organismal response to diet, stress, and aging. Numerous human diseases result from the failure of proteins to fold properly in response to mutation, disrupting the proteome. In the case of the exocytic pathway, this includes proteostasis components that direct folding, and export of proteins from the endoplasmic reticulum (ER). Included here are serpin deficiencies, a class of related diseases that result in a significant reduction of secretion of serine proteinase inhibitors from the liver into serum. In response to misfolding, variants of the serine protease α(1)-antitrypsin (α1AT) fail to exit the ER and are targeted for either ER-associated degradation or autophagic pathways. The challenge for developing α1AT deficiency therapeutics is to understand the PN pathways involved in folding and export. Herein, we review the role of the PN in managing the protein fold and function during synthesis in the ER and trafficking to the cell surface or extracellular space. We highlight the role of the proteostasis boundary to define the operation of the proteome (Annu Rev Biochem 2009;78:959). We discuss how manipulation of folding energetics or the PN by pharmacological intervention could provide multiple routes for restoration of variant α1AT function to the benefit of human health.

Lung disease associated with alpha1-antitrypsin deficiency

α(1)-Antitrypsin (A1AT) is a polyvalent, acute-phase reactant with an extensive range of biological functions that go beyond those usually linked to its antiprotease (serpin) activities. Genetic mutations cause a systemic deficiency of A1AT, leading to liver and pulmonary diseases, including emphysema and chronic bronchitis. The pathogenesis of emphysema, which involves the destruction of small airway structures and alveolar units, is triggered by cigarette smoke and pollutants. The tissue damage caused by these agents is further potentiated by the mutual interactions between apoptosis, oxidative stress, and protease/antiprotease imbalance. These processes lead to the activation of endogenous mediators of tissue destruction, including the lipid ceramide, extracellular matrix proteins, and abnormal inflammatory cell signaling. In this review, we propose that A1AT has a range of actions that are not restricted to protease inhibition but rather extend to mitigate a range of these pathological processes involved in the development of emphysema. We discuss the evidence indicating that A1AT blocks apoptosis by binding and inhibiting active caspase-3 and modulates a broad range of inflammatory responses induced by neutrophils and by lipopolysaccharide and tumor necrosis factor-α signaling.

α(1)-antitrypsin deficiency and inflammation

α(1)-antitrypsin deficiency is an autosomal recessive disorder that results from point mutations in the SERPINA1 gene. The Z mutation (Glu342Lys) accounts for the majority of cases of severe α(1)-antitrypsin deficiency. It causes the protein to misfold into ordered polymers that accumulate within the endoplasmic reticulum of hepatocytes. It is these polymers that form the periodic acid Schiff positive inclusions that are characteristic of this condition. These inclusions are associated with neonatal hepatitis, cirrhosis and hepatocellular carcinoma. The lack of circulating α(1)-antitrypsin exposes the lungs to uncontrolled proteolytic attack and so can predispose the Z α(1)-antitrypsin homozygote to early-onset emphysema. α(1)-antitrypsin polymers can also form in extracellular tissues where they activate and sustain inflammatory cascades. This may provide an explanation for both progressive emphysema in individuals who receive adequate replacement therapy and the selective advantage associated with α(1)-antitrypsin deficiency. Therapeutic strategies are now being developed to block the aberrant conformational transitions of mutant α(1)-antitrypsin and so treat the associated disease.

Alpha-1 antitrypsin deficiency

OBJECTIVE

To review the topic of alpha-1 antitrypsin (AAT) deficiency.

METHOD

Narrative literature review.

RESULTS

Much work has been carried out on this condition with many questions being answered but still further questions remain.

DISCUSSION AND CONCLUSIONS

AAT deficiency is an autosomal co-dominantly inherited disease which affects the lungs and liver predominantly. The clinical manifestations, prevalence, genetics, molecular pathophysiology, screening and treatment recommendations are summarised in this review.

alpha1-Antitrypsin deficiency, chronic obstructive pulmonary disease and the serpinopathies

alpha1-Antitrypsin is the prototypical member of the serine proteinase inhibitor or serpin superfamily of proteins. The family includes alpha1-antichymotrypsin, C1 inhibitor, antithrombin and neuroserpin, which are all linked by a common molecular structure and the same suicidal mechanism for inhibiting their target enzymes. Point mutations result in an aberrant conformational transition and the formation of polymers that are retained within the cell of synthesis. The intracellular accumulation of polymers of mutant alpha1-antitrypsin and neuroserpin results in a toxic gain-of-function phenotype associated with cirrhosis and dementia respectively. The lack of important inhibitors results in overactivity of proteolytic cascades and diseases such as COPD (chronic obstructive pulmonary disease) (alpha1-antitrypsin and alpha1-antichymotrypsin), thrombosis (antithrombin) and angio-oedema (C1 inhibitor). We have grouped these conditions that share the same underlying disease mechanism together as the serpinopathies. In the present review, the molecular and pathophysiological basis of alpha1-antitrypsin deficiency and other serpinopathies are considered, and we show how understanding this unusual mechanism of disease has resulted in the development of novel therapeutic strategies.

Conformational pathology of the serpins: themes, variations, and therapeutic strategies

Point mutations cause members of the serine protease inhibitor (serpin) superfamily to undergo a novel conformational transition, forming ordered polymers. These polymers characterize a group of diseases termed the serpinopathies. The formation of polymers underlies the retention of alpha(1)-antitrypsin within hepatocytes and of neuroserpin within neurons to cause cirrhosis and dementia, respectively. Point mutations of antithrombin, C1 inhibitor, alpha(1)-antichymotrypsin, and heparin cofactor II cause a similar conformational transition, resulting in a plasma deficiency that is associated with thrombosis, angioedema, and emphysema. Polymers of serpins can also form in extracellular tissues where they activate inflammatory cascades. This is best described for the Z variant of alpha(1)-antitrypsin in which the proinflammatory properties of polymers provide an explanation for both progressive emphysema and the selective advantage of this mutant allele. Therapeutic strategies are now being developed to block the aberrant conformational transitions and so treat the serpinopathies.

National Emphysema Treatment Trial state of the art: genetics of emphysema

Although a hereditary contribution to emphysema has been long suspected, severe alpha1-antitrypsin deficiency remains the only conclusively proven genetic risk factor for chronic obstructive pulmonary disease (COPD). Recently, genome-wide linkage analysis has led to the identification of two promising candidate genes for COPD: TGFB1 and SERPINE2. Like multiple other COPD candidate gene associations, even these positionally identified genes have not been universally replicated across all studies. Differences in phenotype definition may contribute to nonreplication in genetic studies of heterogeneous disorders such as COPD. The use of precisely measured phenotypes, including emphysema quantification on high-resolution chest computed tomography scans, has aided in the discovery of additional genes for clinically relevant COPD-related traits. The use of computed tomography scans to assess emphysema and airway disease as well as newer genetic technologies, including gene expression microarrays and genome-wide association studies, has great potential to detect novel genes affecting COPD susceptibility, severity, and response to treatment.

Polymers and inflammation: disease mechanisms of the serpinopathies

Members of the serpin (serine proteinase inhibitor) superfamily play a central role in the control of inflammatory, coagulation, and fibrinolytic cascades. Point mutations that cause abnormal conformational transitions in these proteins can trigger disease. Recent work has defined three pathways by which these conformers cause tissue damage. Here, we describe how these three mechanisms can be integrated into a new model of the pathogenesis of emphysema caused by mutations in the serpin alpha1-antitrypsin.

Screening and familial testing of patients for alpha 1-antitrypsin deficiency

alpha(1)-Antitrypsin deficiency (AATD) is an autosomal-codominant genetic disorder that predisposes individuals to the development of liver and lung disease. AATD is greatly underrecognized and underdiagnosed. Early identification allows preventive measures to be taken, the most important of which is the avoidance of smoking (including the inhalation of second-hand smoke) and exposure to environmental pollutants. Early detection also allows careful lung function monitoring and augmentation therapy while the patient still has preserved lung function. Cost factors and controversies have discouraged the initiation of large-scale screening programs of the newborn and adult populations in the United States and Europe (except for Sweden). There are sound medical reasons for targeted screening. Evidence-based recommendations for testing have been published by the American Thoracic Society/European Respiratory Society task force, which take potential social, psychological, and ethical adverse factors into consideration. This review discusses rationales for testing and screening for AATD in asymptomatic individuals, family members, and the general population, weighing benefits against potential psychological, social, and ethical implications of testing. For most, negative issues are outweighed by the benefits of testing. AATD testing should be routine in the management of adults with emphysema, COPD, and asthma with incompletely reversible airflow obstruction.