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      A challenging diagnosis of alpha-1-antitrypsin deficiency: identification of a patient with a novel F/Null phenotype

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          Abstract

          Alpha-1-antitrypsin (A1AT) deficiency is a genetic disease characterized by low levels and/or function of A1AT protein. A1AT deficiency can result in the development of COPD, liver disease, and certain skin conditions. The disease can be diagnosed by demonstrating a low level of A1AT protein and genotype screening for S and Z mutations, which are the most common. However, there are many genetic variants in A1AT deficiency, and this screening may miss rarer cases, such as those caused by dysfunctional protein. We identified a patient with a previously unreported F/null phenotype that was missed by routine screening. This case highlights the wide variation in possible mutations, limitations in diagnostics, and the importance of combining clinical suspicion with measurement of protein levels, phenotypic analysis, and in appropriate cases expanded genetic analysis.

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          Most cited references 9

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          Clinical practice. Alpha1-antitrypsin deficiency.

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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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              Alpha-1 antitrypsin Null mutations and severity of emphysema.

              Alpha-1 antitrypsin (AAT) deficiency is an autosomal-codominant disorder, caused by mutations in the SERPINA1 gene on chromosome 14. Individuals affected by the most common mutations, SZ and ZZ, have serum AAT concentrations of 25% and 15% of normal levels, and present a higher risk of emphysema. Mutations causing total absence of serum AAT (Null mutations) were suggested to be associated with very early onset emphysema but their clinical phenotype is poorly known. Absence of AAT in Null mutations results in more severe emphysema as compared to ZZ and SZ. We genotyped all known Dutch subjects (n=12) with absent serum AAT, and compared their lung function values (FEV1 and KCO) with those of individuals with ZZ and SZ genotype, matched for age and smoking history. All subjects with absent serum AAT presented homozygous Null mutations. In three subjects, a new mutation in exon 2 of the SERPINA1 gene was found. Subjects with Null mutations showed significantly lower lung function values than SZ and ZZ individuals (p=0.000 and 0.001 for FEV1 and KCO, respectively). In all groups, there was a positive correlation between serum AAT and lung function values (p=0.025 and 0.014 for FEV1 and KCO, respectively). Serum levels of AAT are correlated with the severity of pulmonary phenotype. Subjects with Null mutations should be considered a subgroup at particularly high risk of emphysema within AAT deficiency (AATD). Early detection of carriers of this genotype would be important for preventive and therapeutic interventions.
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                Author and article information

                Journal
                Allergy Asthma Clin Immunol
                Allergy, Asthma, and Clinical Immunology : Official Journal of the Canadian Society of Allergy and Clinical Immunology
                BioMed Central
                1710-1484
                1710-1492
                2011
                13 November 2011
                : 7
                : 1
                : 18
                Affiliations
                [1 ]Department of Medicine, Section of Allergy and Immunology, The Pennsylvania State University Milton S. Hershey Medical Center, 500 University Dr., Hershey, PA 17033, USA
                [2 ]Department of Biochemistry and Molecular Biology, The Pennsylvania State University College of Medicine, 500 University Dr., Hershey, PA 17033, USA
                [3 ]Department of Laboratory Medicine and Pathology, Mayo Clinic College of Medicine, Hilton 2-10D, 200 First St. SW, Rochester, MN, 55905, USA
                Article
                1710-1492-7-18
                10.1186/1710-1492-7-18
                3229436
                22078084
                Copyright ©2011 Ringenbach et al; licensee BioMed Central Ltd.

                This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

                Categories
                Case Report

                Immunology

                genotype, diagnostic testing, phenotype, alpha-1-antitrypsin

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