HPE Alpha 1 Antitrypsin Deficiency | Page 12

The importance of early detection and screening Because AATD is still largely underdiagnosed (<10% of what would be expected from epidemiological data), early detection of AATD subjects remains a primary concern and must be conducted in reference centres that can provide the best diagnostic tools. The laboratory diagnosis of AATD has evolved over the past 50 years, since the first cases of the disorder were reported. The diagnostic procedure is complex because it comprises both quantitative and qualitative tests. The use of dried blood spots (drops of blood that have been dried onto a special filter paper) for the routine laboratory diagnosis of AATD has become widespread and has facilitated centralisation of testing. 22–24 This kind of matrix allows easier preservation and shipping of samples, thereby allowing wide detection or screening programs for AATD. 11 Determination of AAT plasma level is the first crucial analysis, usually performed by nephelometry. Systemic inflammatory status parallels increased levels of AAT and this increase might mask the presence of AATD variants; 25 for this reason, many reference centres perform the simultaneous determination of C-reactive protein and AAT in order to avoid the misdiagnosis of heterozygote- subjects carrying intermediate AATD genotypes. 26 Most laboratories and screening programs perform genotyping for the two most common disease-associated alleles, S and Z; usually the presence or absence of S and Z variants is established using genotype-based, allele-specific amplification by quantitative polymerase chain reaction. Reflex testing for the identification of other variants is usually performed using isoelectric focusing (IEF). The principle of IEF is the separation of proteins based on their charge in a pH gradient fixed in the gel. AAT phenotypes are classified by a coding system in which the inherited alleles are usually letters that denote the migration of the molecule in an isoelectric pH gradient from A (for anodal variants) to Z (for slower migrating variants). Many AAT genetic variants reflect point mutations in the gene sequence leading to amino acid substitutions, which may affect the electrophoretic References 1 Green CE et al. PiSZ alpha-1 antitrypsin deficiency (AATD): pulmonary phenotype and prognosis relative to PiZZ AATD and PiMM COPD. Thorax. 2015;70(10):939–45. 2 Blanco I et al. Alpha-1 antitrypsin Pi*Z gene frequency and Pi*ZZ genotype numbers worldwide: an update. Int J Chron Obstruct Pulmon Dis 2017;12:561–9. 3 Blanco I et al. Alpha-1 antitrypsin Pi*SZ genotype: estimated prevalence and number of SZ subjects worldwide. Int J Chron Obstruct Pulmon Dis 2017;12:1683–94. 4 McCarthy C et al. Epidemiology of rare lung diseases: The challenges and opportunities to improve research and knowledge. Adv Exp Med Biol 2017;1031:419–42. 5 Blanco I et al. Estimated numbers and prevalence of PI*S and PI*Z alleles of alpha1-antitrypsin deficiency in European countries. Eur Respir J 2006;27(1):77–84. 6 Greulich T et al. The prevalence of diagnosed α1-antitrypsin deficiency and its comorbidities: results from a large population- based database. Eur Respir J 2017;49(1). 7 Al-Jameil N et al. The prevalence of PI*S and PI*Z SERPINA1 alleles in healthy individuals and COPD patients in Saudi Arabia: A case-control study. Medicine (Baltimore) 2017;96(42):e8320. 8 de Serres FJ et al. PI S and PI Z alpha-1 antitrypsin deficiency worldwide. A review of existing genetic epidemiological data. Monaldi Arch Chest Dis 2007;67(4):184–208. 9 Zhumagaliyeva A et al. Case- finding for alpha1-antitrypsin deficiency in Kazakh patients with COPD. Multidiscip Respir Med 2017;12:23. 10 Seyama K et al. A nationwide epidemiological survey of alpha1- antitrypsin deficiency in Japan. Respir Investig 2016;54(3):201–6. 11 Miravitlles M et al. Laboratory testing of individuals with severe alpha1-antitrypsin deficiency in three European centres. Eur Respir J 2010;35(5):960–8. 121 Ferrarotti I et al. Prevalence and phenotype of subjects carrying rare variants in the Italian registry for alpha1- antitrypsin deficiency. J Med Genet 2005;42(3):282–7. 12 | 2019 | hospitalpharmacyeurope.com 13 Rodriguez-Frias F et al. Rare alpha-1-antitrypsin variants: are they really so rare? Ther Adv Respir Dis 2012;6(2):79–85. 14 Blanco I et al. Alpha-1 antitrypsin deficiency PI*Z and PI*S gene frequency distribution using on maps of the world by an inverse distance weighting (IDW) multivariate interpolation method. Hepat Mon 2012;12(10 HCC):e7434. 15 Stockley RA et al. Alpha-1 antitrypsin deficiency: the European experience. COPD 2013;10 Suppl 1:50–3. 16 Stoller JK et al. Formation and current results of a patient- organized registry for alpha(1)- antitrypsin deficiency. Chest 2000;118(3):843–8. 17 Luisetti M et al. Italian registry of patients with alpha-1 antitrypsin deficiency: general data and quality of life evaluation. COPD. 2015;12 Suppl 1:52–7. 18 Lara B, Miravitlles M. Spanish registry of patients with alpha-1 antitrypsin deficiency; comparison of the characteristics of PISZ and PIZZ individuals. COPD 2015;12 Suppl 1:27–31. 19 Fregonese L, Stolk J. Hereditary alpha-1-antitrypsin deficiency and its clinical mobility of the resulting AAT protein, exhibiting a characteristic banding pattern that can be compared to known reference samples. Where there are discrepancies between quantitative and qualitative results, second level investigations, such as gene sequencing, are mandatory. Whole gene sequencing can detect insertions, deletions and stop mutations, in order to identify rare and Null variants not detectable with other techniques such as isoelectric focusing. Some laboratories perform a third level investigation that consists of intron sequencing to find some intronic variants (such as Q0porto, Q0madrid, Mwhitstable). The optimal results of genotyping are obtained when performed in expert laboratories and interpreted in conjunction with the protein level and familial relationships by experienced AATD personnel. 27 Testing patients’ relatives should be considered after identification of an index case. The 2003 American Thoracic Society/European Respiratory Society document outlines the testing recommendations to identify affected subjects. 28 Although the risk is particularly high in subjects with early COPD onset, rapid decline in lung function or family history of AATD, the recommendation applies to all subjects with COPD, regardless of age, smoking history, emphysema distribution or race. It is widely quoted that the prevalence of AATD among individuals with COPD is approximately 1–2%. 28 In the past, young adults presenting with severe lung disease, in particular basal panlobular emphysema, were the most frequently tested; however, existing guidelines recommend testing of all COPD patients, irrespective of age and severity. In fact, patients can demonstrate the same clinical features as non-deficient COPD, including increased evidence of bronchiectasis, chronic bronchitis, bacterial colonisation, frequent exacerbations, impaired health status and a degree of reversibility of airflow obstruction. Therefore, the World Health Organization guidance for testing every patient with a diagnosis of COPD or adult-onset asthma for AATD should be standard. 29 This recommendation has been strengthened by the European Respiratory Society Statement. 27 consequences. Orphanet J Rare Dis 2008;3:16. 20 Carroll TP et al. The prevalence of alpha-1 antitrypsin deficiency in Ireland. Respir Res. 2011;12:91. 21 Luisetti M, Seersholm N. Epidemiology of alpha1- antitrypsin deficiency. Thorax 2004;59:164–9. 22 Wencker M et al. Screening for alpha1-Pi deficiency in patients with lung diseases Eur Respir J 2002;20:319–24. 23 Gorrini M et al. Validation of a rapid, simple method to measure alpha1-antitrypsin in human dried blood spots. Clin Chem 2006;52(5):899–901. 24 Zillmer LR et al. Validation and development of an immunonephelometric assay for the determination of alpha-1 antitrypsin levels in dried blood spots from patients with COPD. J Bras Pneumol 2013;39(5):547–54. 25 Zorzetto M et al. SERPINA1 gene variants in individuals from the general population with reduced alpha1-antitrypsin concentrations. Clin Chem 2008;54(8):1331–8. 26 Ottaviani S et al. C reactive protein and alpha1-antitrypsin: relationship between levels and gene variants. Transl Res 2011;157(6):332–8. 27 Miravitlles M et al. European Respiratory Society statement: diagnosis and treatment of pulmonary disease in α 1 - antitrypsin deficiency. Eur Respir J 2017;50(5). 28 Alpha-1 Antitrypsin Deficiency Task Force. American Thoracic Society/European Respiratory Society. Standards for the diagnosis and management of individuals with alpha1- antitrypsin deficiency. Am J Respir Crit Care Med 2003;168:818–900. 29 Alpha 1-antitrypsin deficiency: memorandum from a WHO meeting. Bull World Health Organ 1997;75(5):397–415.