Alpha-1-antitrypsin deficiency

Alpha-1-antitrypsin deficiency (AATD) is a rare genetic disorder associated with the development of liver and lung disease. AAT is a 52-kD glycoprotein, produced mainly by hepatocytes and secreted into the blood. Agglomeration of the AAT-protein in hepatocytes can result in liver disease. Exposure to smoke is the major risk factor for the development of lung disease characterised as early chronic obstructive lung disease (COPD). Diagnosis is based on the analysis of the AAT genotype and phenotype. The measurement of the AAT serum level is useful as screening test. Liver biopsy is not necessary to establish the diagnosis. Therapy for AAT-related liver disease is supportive, a specific therapy is not available. AATD is a rare condition (1:5000-10000) and, as a consequence, data and information on diagnosis and treatment are not easily accessible. This chapter provides a comprehensive overview on AATD, covering basic biology, diagnostic and therapeutic approaches.     

Alpha-1-antitrypsin deficiency: a biological enigma.

The association of certain forms of liver disease and a deficiency of alpha-1-antitrypsin is an observation which raises the possibility that other forms of liver disease ultimately will be found to have as their proximate cause a defined metabolic aberration, which may in turn be inherited. Although alpha-1-antitrypsin deficiency is a genetically determined error of protein synthesis, environmental factors, unrecognised at present, are required for the disease to become overt. Thus, this interesting association may herald an increasing number of clinical diseases in which the interaction of environmental stimuli and single genetically determined aberrations are crucially important. The diseases to which we succumb may be largely determined by a genetically determined susceptibility, a point of view which was stated so well by Archibalt Garrod in his essay Inborn Factors in Disease published nearly half a century ago.     

Alpha-1-antitrypsin deficiency asthma and allergy

The biochemistry, genetics and pathology of alpha-1-anti-trypsin deficiency are reviewed. The geographical distribution in Europe of more current phenotypes M, SZ is discussed. Two cases of alpha-1- anti-trypsin are presented one homozygotic ZZ non-smoker without any respiratory pathology and one heterozygotic SZ heavy smoker with a severe chronic obstructive pulmonary disease and reversibility to Beta-2-mimetics suggesting asthma. The relationship between alpha-1-antitrypsin and asthma is discussed and general measures of treatment or prevention suggested.     

Alpha-1-antitrypsin deficiency presenting as bronchiectasis

We describe three patients with the clinical and radiographic features of progressive bronchiectasis, and without evidence of emphysema, associated with deficiency of alpha-1-antitrypsin. The association of hereditary alpha-1-antitrypsin deficiency and pulmonary emphysema is well recognized (Eriksson 1965). About half of these subjects also have chronic bronchitis as defined by persistent sputum production (Tobin et al. 1983). Bronchographically proven bronchiectasis without apparent emphysema has been reported in only one subject with alpha-1-antitrypsin deficiency (Longstretch et al. 1975).     

Alpha-1-antitrypsin deficiency in a large sibship

We studied alpha 1-antitrypsin deficiency in a large family of 10 siblings: 3 subjects had PiZZ phenotype, but only 1 had emphysema; 2 subjects had no respiratory complaint. The patient with emphysema was a heavy smoker. According to the literature, this case suggests that, in PiZZ phenotype, emphysema appears earlier and is more severe if the patients smoke.     

Alpha-1-antitrypsin and the pathogenesis of emphysema

The review examines the relationship between alpha₁-antitrypsin (α ₁AT) and emphysema. Although other defects occur in subjects with alpha₁-antitrypsin deficiency, it seems likely that a reduction in inhibition due to loss of this inhibitor explains their emphysema. There is a great deal of controversy, however, concerning the role of alpha₁-antitrypsin in subjects without inherited deficiency. There is uncertainty about the presence and function of other elastase inhibitors in the peripheral lung. The function of lungα ₁AT and the presence of elastase activity are dependent upon the techniques used and this probably accounts for different results between research groups. In addition, other relevant factors such as which enzymes cause lung elastolysis, control of neutrophil chemotaxis, and mechanisms of elastin synthesis and repair are less well studied. The overall conclusion is that many aspects of the elastase/antielastase hypothesis of emphysema are poorly understood. Without further information the true role ofα ₁AT will remain largely speculative.     

Alpha-1-antitrypsin replacement therapy: current status

PURPOSE OF REVIEW: Alpha-1-antitrypsin deficiency is a relatively common genetic disease that predisposes to the development of early-onset emphysema and, in some instances, liver disease. The use of alpha-1-antitrypsin replacement therapy in the treatment of alpha-1-antitrypsin deficiency related emphysema is much debated and the purpose of this review is to examine the results of recent studies. We will comment briefly on the pathogenesis and epidemiology of the disease together with new therapeutic approaches currently under intense research. RECENT FINDINGS: Several nonrandomized observational studies and one meta-analysis on the clinical effectiveness of alpha-1-antitrypsin replacement treatment showed a favourable result towards reducing forced expiratory volume in 1 s (FEV1) deterioration in alpha-1-antitrypsin-deficient individuals with moderate lung disease or accelerated FEV1 decline. Improved ways of monitoring disease progression, including computed tomography scanning and exacerbations, are being proposed as primary endpoints. Apart from one small randomized, placebo-controlled trial using computed tomography scanning, which showed a trend toward preservation of lung density on scanning with treatment, the literature lacks proof of effectiveness from large randomized trials. SUMMARY: There might be a possible, but so far unproven, role of alpha-1-antitrypsin augmentation therapy in reducing the progression of emphysema in subsets of patients with alpha-1-antitrypsin deficiency. Placebo-controlled, randomized clinical trials are required to draw firm conclusions. Recent advances in the understanding of the molecular pathology provide opportunities for development of new therapeutic targets for this genetic disorder.     

Alpha-1-antitrypsin deficiency: diagnosis and treatment

Alpha-1-antitrypsin (AT) deficiency was first described in the late 1960s in patients with severe pulmonary emphysema. The recognition of AT deficiency as a cause of emphysema then led to what is still the prevailing theory for the pathogenesis of emphysema, the protease-antiprotease theory. Soon it was found that AT deficiency accounted for a significant number of cases of neonatal liver disease that were previously categorized as idiopathic. We now know that AT deficiency is the most common genetic cause of neonatal liver disease and the most frequent diagnosis necessitating liver transplantation. It has also been shown to cause chronic liver disease, cryptogenic cirrhosis, and hepatocellular carcinoma in adults never previously known to have liver disease in infancy or childhood. Observations indicate that genetic traits unlinked to the AT gene or environmental factors predispose to or protect AT-deficient individuals from liver disease.     

Alpha-1-antitrypsin phenotypes in patients with renal arterial fibromuscular dysplasia

Fibromuscular dysplasia (FMD) is a significant cause of renal artery stenosis, especially in young females. A rare association between FMD and alpha 1-antitrypsin (alpha 1-AT) deficiency has been reported. We compared the alpha 1-AT phenotype distribution in 83 patients with renal arterial FMD with those published for Australian populations. alpha 1-AT phenotyping was performed by isoelectric focusing between pH 4.2 and pH 4.9 on polyacrylamide gels with PiM1M2, PiFM (non-deficiency alleles), PiMS and PiMZ (deficiency alleles) markers. Following phenotyping, alpha 1-AT genotyping was performed in 10 patients to confirm the presence of S and/or Z alleles. The phenotype distribution and allele frequencies were similar to those reported for normal subjects from two Australian populations (72 (86.7%) PiMM phenotype, one (1.2%) PiFM, seven (8.4%) PiMS, two (2.4%) PiMZ and one (1.2%) PiSZ), suggesting that alpha 1-AT deficiency is not a common aetiological factor in renal arterial FMD. However, despite FMD being three times less common in males than females, and carotid artery dissection being a rare occurrence, a male with PiMS deficiency phenotype presented with internal carotid artery dissection and had bilateral renal artery FMD. Further, a patient with PiSZ deficiency phenotype was one of two sisters with FMD and was more severely affected than her PiMM normal phenotype sibling. These two patients from the present series together with nine culled from the literature with alpha 1-AT deficiency phenotype and FMD suggest that the chance combination of alpha 1-AT deficiency and FMD may predispose to severe manifestations of FMD.     

Alpha-1-antitrypsin phenotypes in rheumatoid arthritis and systemic lupus erythematosus.

Alpha-1-antitrypsin phenotypes were determined in 37 patients with rheumatoid arthritis and 40 patients with systemic lupus erythematosus. No significant increase in non-MM phenotypes was found. It appears that alpha-1-antitrypsin phenotypes neither predispose to the development nor enhance the severity of the two rheumatic diseases.     

Alpha-1-antitrypsin: an ignored protein in understanding liver disease

alpha 1AT should no longer be ignored by hepatologists with regard to its role in protecting the liver from injury. This protective role needs further definition with regard to protease inhibition, immunologic control, and functional inactivation. Severe deficiency of alpha 1AT clearly predisposes to definable types of liver disease not only in infants and children, but at the other end of the spectrum in elderly adults. It is unfortunate that the pathophysiology of human and animal alpha 1AT related liver injury is not as readily apparent as in pulmonology conditions. However, it is time to digest the tremendous progress that has evolved in that field in relating alpha 1AT to emphysema. Cirrhosis of the liver should be studied in relationship to the pathophysiology demonstrated by our colleagues to be important in "cirrhosis of the lung." The diagnosis of alpha 1AT deficiency and the course of the associated liver disease have been reviewed and updated. Prevention and cure have been demonstrated to be possible but neither method has universal applicability. In contrast, other potential therapeutic endeavors, although not presently proved to be efficacious, with time and research will provide methodologies for the treatment of this disorder as well as insight into mechanisms of general liver injury not previously appreciated.