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      Application of a diagnostic algorithm for the rare deficient variant Mmalton of alpha-1-antitrypsin deficiency: a new approach

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          Abstract

          Background and objectives

          Alpha-1-antitrypsin deficiency (AATD) is associated with a high risk for the development of early-onset emphysema and liver disease. A large majority of subjects with severe AATD carry the ZZ genotype, which can be easily detected. Another rare pathologic variant, the Mmalton allele, causes a deficiency similar to that of the Z variant, but it is not easily recognizable and its detection seems to be underestimated. Therefore, we have included a rapid allele-specific genotyping assay for the detection of the Mmalton variant in the diagnostic algorithm of AATD used in our laboratory. The objective of this study was to test the usefulness of this new algorithm for Mmalton detection.

          Materials and methods

          We performed a retrospective revision of all AATD determinations carried out in our laboratory over 2 years using the new diagnostic algorithm. Samples with a phenotype showing one or two M alleles and AAT levels discordant with that phenotype were analyzed using the Mmalton allele-specific genotyping assay.

          Results

          We detected 49 samples with discordant AAT levels; 44 had the MM and five the MS phenotype. In nine of these samples, a single rare Mmalton variant was detected. During the study period, two family screenings were performed and four additional Mmalton variants were identified.

          Conclusion

          The incorporation of the Mmalton allele-specific genotyping assay in the diagnostic algorithm of AATD resulted in a faster and cheaper method to detect this allele and avoided a significant delay in diagnosis when a sequencing assay was required. This methodology can be adapted to other rare variants. Standardized algorithms are required to obtain conclusive data of the real incidence of rare AAT alleles in each region.

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          Most cited references 33

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          Alpha1-antitrypsin deficiency.

          Alpha1-antitrypsin deficiency is a genetic disorder that affects about one in 2000-5000 individuals. It is clinically characterised by liver disease and early-onset emphysema. Although alpha1 antitrypsin is mainly produced in the liver, its main function is to protect the lung against proteolytic damage from neutrophil elastase. The most frequent mutation that causes severe alpha1-antitrypsin deficiency arises in the SERPINA 1 gene and gives rise to the Z allele. This mutation reduces concentrations in serum of alpha1 antitrypsin by retaining polymerised molecules within hepatocytes: an amount below the serum protective threshold of 11 micromol/L increases risk for emphysema. In addition to the usual treatments for emphysema, infusion of purified alpha1 antitrypsin from pooled human plasma represents a specific treatment and raises the concentrations in serum and epithelial-lining fluid above the protective threshold. Evidence suggests that this approach is safe, slows the decline of lung function, could reduce infection rates, and might enhance survival. However, uncertainty about the cost-effectiveness of this expensive treatment remains.
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            Worldwide racial and ethnic distribution of alpha1-antitrypsin deficiency: summary of an analysis of published genetic epidemiologic surveys.

             F Serres (2002)
            Alpha1-antitrypsin (AAT) deficiency is a genetic disease that is widely known in Europe as a disease of white individuals, who, along with their descendants in other parts of the world, are at the highest risk for liver and/or lung disease. There is a limited database of individuals affected by this disease worldwide. It has been estimated, for example, that there are 70,000 to 100,00 individuals affected in the United States, with comparable numbers in Europe. Genetic epidemiologic studies in the peer-reviewed literature have been used in an exploratory study to estimate the number of carriers and the number of those individuals who are homozygous or heterozygous for the two most common defective alleles for AAT deficiency in 58 individual countries. The total country database of 373 control cohorts has been combined to estimate the numbers of carriers and deficiency allele combinations for PiS and PiZ in 11 geographic regions and worldwide. The study was designed to be illustrative rather than comprehensive, and more detailed publication of the enormous database developed in this exploratory study is planned. The database presented indicates that in a total population of 4.4 billion in the countries surveyed worldwide, there are at least 116 million carriers (PiMS and PiMZ) and 3.4 million deficiency allele combinations (PiSS, PiSZ, and PiZZ). Furthermore, this database demonstrates that AAT deficiency is found in various populations of African blacks, Arabs and Jews in the Middle East, whites in Australia/New Zealand, Europe, and North America, central Asians, far east Asians, and southeast Asians. These data demonstrate that AAT deficiency is not just a disease of whites in Europe, but that it affects individuals in all racial subgroups worldwide. In addition, AAT deficiency may be one of the most common serious hereditary disorders in the world.
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              Delay in diagnosis of alpha1-antitrypsin deficiency: a continuing problem.

              Alpha1-antitrypsin (AAT) deficiency is common but under-recognized. A 1994 mail survey showed a long delay between the onset of symptoms and the initial diagnosis of AAT deficiency. In 2003, we carried out a similar mail survey of AAT-deficient individuals to determine whether any delay in diagnosis experienced by individuals with a more recent diagnosis had become shorter. We also determined whether individuals living near medical centers with an expressed interest in AAT deficiency experienced shorter diagnostic delays than those living at a distance. Results from mail surveys of two different cohorts were compared: a 1994 survey of 304 individuals with severe AAT deficiency and a 2003 survey of 1,953 AAT-deficient individuals. In the 2003 survey cohort, diagnostic delay intervals were analyzed by calendar year of initial diagnosis, rural vs urban residence, visit to a liver or lung specialist within the last year, and living within 50 miles of a medical center with particular expertise in AAT deficiency. One thousand nine hundred fifty-three individuals responded to the 2003 mail survey (37.4%). In the 2003 cohort, the mean +/- SD diagnostic delay was 5.6 +/- 8.5 years, compared with 7.2 +/- 8.3 years for the 1994 cohort (p = 0.002). In the 2003 cohort, younger patients and male patients experienced shorter diagnostic delays than older patients and female patients (p < 0.0001 and p = 0.007, respectively). For example, the delay was 6.5 +/- 8.8 years for those born in the 1940s, as compared with 0.43 +/- 1.08 years for those born after 1980. Neither urban residence nor living near a center with expertise in AAT deficiency were associated with a shortened diagnostic delay interval. Although these results show some improvement in the mean diagnostic delay in the 9-year period separating the two studies, under-recognition of AAT deficiency persists. Diagnostic delay of AAT deficiency is longer in women and in older individuals. Educational efforts are underway to enhance clinicians' diagnostic suspicion of AAT deficiency and permit earlier diagnosis and attendant benefits.
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                Author and article information

                Journal
                Int J Chron Obstruct Pulmon Dis
                Int J Chron Obstruct Pulmon Dis
                International Journal of COPD
                International Journal of Chronic Obstructive Pulmonary Disease
                Dove Medical Press
                1176-9106
                1178-2005
                2016
                11 October 2016
                : 11
                : 2535-2541
                Affiliations
                [1 ]Liver Pathology Unit, Department of Biochemistry and Microbiology, Hospital Universitari Vall d’Hebron, Universitat Autònoma de Barcelona (UAB), Barcelona, Spain
                [2 ]Vall d’Hebron Institut de Recerca (VHIR), Barcelona, Spain
                [3 ]Pneumology Department, Hospital Universitari Vall d’Hebron, Barcelona, Spain
                [4 ]Biochemistry Department, Hospital Universitari Vall d’Hebron, Barcelona, Spain
                [5 ]CIBER of Respiratory Diseases, Barcelona, Spain
                [6 ]CIBER of Liver and Digestive Diseases, Instituto Nacional de Salud Carlos III, Madrid, Spain
                Author notes
                Correspondence: Francisco Rodríguez-Frías, Liver Pathology Unit, Department of Biochemistry and Microbiology, Hospital Universitari Vall d’Hebron, Universitat Autònoma de Barcelona, Passeig Vall d’Hebron 119-129, 08035 Barcelona, Spain, Tel +34 932 746 100, Fax +34 934 893 895, Email frarodri@ 123456gmail.com
                Article
                copd-11-2535
                10.2147/COPD.S115940
                5113155
                © 2016 Belmonte et al. This work is published and licensed by Dove Medical Press Limited

                The full terms of this license are available at https://www.dovepress.com/terms.php and incorporate the Creative Commons Attribution – Non Commercial (unported, v3.0) License ( http://creativecommons.org/licenses/by-nc/3.0/). By accessing the work you hereby accept the Terms. Non-commercial uses of the work are permitted without any further permission from Dove Medical Press Limited, provided the work is properly attributed.

                Categories
                Original Research

                Respiratory medicine

                serum levels, rare variant, phenotyping, genotyping, emphysema

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