Ferrarotti et al. Orphanet Journal of Rare Diseases 2014, 9:172 http://www.ojrd.com/content/9/1/172 RESEARCH Open Access Identification and characterisation of eight novel SERPINA1 Null mutations Ilaria Ferrarotti1,7*†, Tomás P Carroll2†, Stefania Ottaviani1, Anna M Fra3, Geraldine O’Brien2, Kevin Molloy2, Luciano Corda4, Daniela Medicina5, David R Curran6, Noel G McElvaney2 and Maurizio Luisetti1,7 Abstract Background: Alpha-1 antitrypsin (AAT) is the most abundant circulating antiprotease and is a member of the serine protease inhibitor (SERPIN) superfamily. The gene encoding AAT is the highly polymorphic SERPINA1 gene, found at 14q32.1. Mutations in the SERPINA1 gene can lead to AAT deficiency (AATD) which is associated with a substantially increased risk of lung and liver disease. The most common pathogenic AAT variant is Z (Glu342Lys) which causes AAT to misfold and polymerise within hepatocytes and other AAT-producing cells. A group of rare mutations causing AATD, termed Null or Q0, are characterised by a complete absence of AAT in the plasma. While ultra rare, these mutations confer a particularly high risk of emphysema. Methods: We performed the determination of AAT serum levels by a rate immune nephelometric method or by immune turbidimetry. The phenotype was determined by isoelectric focusing analysis on agarose gel with specific immunological detection. DNA was isolated from whole peripheral blood or dried blood spot (DBS) samples using a commercial extraction kit. The new mutations were identified by sequencing all coding exons (II-V) of the SERPINA1 gene. Results: We have found eight previously unidentified SERPINA1 Null mutations, named: Q0cork,Q0perugia,Q0brescia, Q0torino,Q0cosenza,Q0pordenone,Q0lampedusa, and Q0dublin . Analysis of clinical characteristics revealed evidence of the recurrence of lung symptoms (dyspnoea, cough) and lung diseases (emphysema, asthma, chronic bronchitis) in M/Null subjects, over 45 years-old, irrespective of smoking. Conclusions: We have added eight more mutations to the list of SERPINA1 Null alleles. This study underlines that the laboratory diagnosis of AATD is not just a matter of degree, because the precise determination of the deficiency and Null alleles carried by an AATD individual may help to evaluate the risk for the lung disease. Keywords: Alpha-1 antitrypsin deficiency, Q0 mutation, Lung diseases, Serpins Background acid, 52 kDa glycoprotein with three asparagine-linked Alpha-1 antitrypsin (AAT) is a serine protease inhibitor, carbohydrate side chains [1]. AAT is an acute phase encoded by the SERPINA1 gene on the long arm of protein produced predominantly by hepatocytes, but chromosome 14 at 14q32.1. The gene is comprised of AAT synthesis also occurs in mononuclear phagocytes, four coding exons (II, III, IV, and V), three untranslated neutrophils, and airway and intestinal epithelial cells exons (Ia, Ib, and Ic) in the 5′ region and six introns. [2]. Consistent with a role as an important acute phase Following translation, the 24 amino acid signal peptide reactant, hepatocytes express approximately 200 times is removed and the mature polypeptide is a 394 amino more AAT mRNA than other cells [3] and serum levels rapidly increase several-fold during the acute phase * Correspondence: [email protected] response [4]. The primary function of AAT is the regula- †Equal contributors tion of serine proteases, and the chief site of action is the 1Centre for Diagnosis of Inherited Alpha-1 Antitrypsin Deficiency, Laboratory lungs where it protects the fragile alveolar tissues from of Biochemistry and Genetics, Institute for Respiratory Disease, Fondazione IRCCS Policlinico San Matteo, Pavia, Italy proteolytic degradation during inflammatory responses. 7Department of Molecular Medicine, University of Pavia, Pavia, Italy Full list of author information is available at the end of the article © 2014 Ferrarotti 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/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Ferrarotti et al. Orphanet Journal of Rare Diseases 2014, 9:172 Page 2 of 9 http://www.ojrd.com/content/9/1/172 In addition to its undoubted anti-protease properties, unclear, and is hampered by a lack of general awareness there is accumulating evidence that AAT plays a key of AATD and inherent flaws in diagnostic strategies. anti-inflammatory role [5]. We report here eight cases of previously unidentified Alpha-1 antitrypsin deficiency (AATD) (MIM # 613490) Null SERPINA1 mutations in the Italian and Irish is an inherited condition caused by mutations within populations. the polymorphic SERPINA1 gene and is characterised by decreased serum AAT concentrations. AATD is an Methods under-diagnosed condition and the majority of cases The diagnostic algorithm for diagnosis of AATD was remain undiagnosed. The World Health Organisation applied as previously reported [20]. The probands were (WHO), the American Thoracic Society (ATS), and the referred to the Italian or Irish National Reference Centres European Respiratory Society (ERS) advocate a targeted for the Diagnosis of AATD, situated in Pavia and Brescia screening approach for the detection of AATD in at risk (Italy), and Dublin (Ireland), respectively. Where possible, populations, specifically chronic obstructive pulmonary relatives were analysed and family trees were created disease (COPD), non-responsive asthma, cryptogenic liver (online Additional file 1). Family members included in disease and in first degree relatives of known AATD the study or their parents gave written informed consent. patients. Over 100 mutations leading to AAT deficiency All procedures were in accordance with the declaration of have been identified to date and are associated with Helsinki and approved by the local ethics committees. varying degrees of risk for lung and liver disease. AATD is Clinical data were obtained from direct observation or associated with increased risk of cutaneous panniculitis medical charts. [6] and case reports have linked AATD to vasculitis [7], AAT measurements were performed by a rate immune and Wegener’s granulomatosis [8] with the Z allele over- nephelometric method (Array 360 System; Beckman- represented in subsets of ANCA-associated vasculitis [9]. Coulter) or by immune turbidimetry (Beckman Coulter The most common mutations known to cause AATD AU5400). The phenotype was determined by isoelectric are the dysfunctional Z (Glu342Lys) and S (Glu264Val) focusing analysis (IEF) on agarose gel with specific mutations. The Z mutation leads to a severe plasma immunological detection [21]. DNA was isolated from deficiency and is the most common clinically significant whole peripheral blood or dried blood spot (DBS) samples allele. The majority of individuals diagnosed with severe using a commercial extraction kit (DNA IQ System, Pro- AATD are homozygous for the Z mutation, and have mega or PAXgene Blood DNA kit, PreAnalytix or DNA circulating AAT levels reduced to 10-15% of normal. This Blood Mini kit, Qiagen). The new mutations were identi- is because the Z mutation prompts the AAT protein fied by sequencing all coding exons (II-V) of the AAT gene to polymerise and accumulate within the endoplasmic (SERPINA1, RefSeq: NG_008290), as previously described reticulum of hepatocytes, thus causing impaired secre- [20,22], using the CEQ 8800 genetic analysis System tion [10]. The rate of polymer formation for S is much (Beckman Coulter) or the Big Dye Terminator Cycle slower than Z AAT, leading to reduced retention of Sequencing Kit 3.1 (Applied Biosystem) with the 3130 protein within hepatocytes, milder plasma deficiency, Genetic Analyzer. and a negligible risk of disease in MS heterozygotes [11,12]. However, there is a risk of lung disease in Results compound heterozygotes. For example, if the slowly The specific mutations are summarized in Table 1. The polymerising S variant of AAT is inherited with a rapidly eight new Null mutations have been conventionally polymerising variant such as Z, the two variants when named Q0cork,Q0perugia,Q0brescia,Q0torino,Q0cosenza, co-expressed can interact to form heteropolymers, lead- ing to cirrhosis and plasma deficiency [13]. Table 1 Description of the eight new SERPINA1 Null SERPINA1 The ultra rare family of mutations termed mutations identified silent or Null are characterised by a complete absence Variant Mutation of AAT in the plasma. Null (also called Q0) mutations Q0cork T180ACA,delCA > Ter190TAA are caused by a variety of different mechanisms includ- Q0perugia V239GTG, delG > Ter241TGA ing large gene deletions [14], intron mutations [15], nonsense mutations [16], and frameshift mutations Q0brescia E257GAG > TerTAG [17]. In some cases, Null variants are synthesised in the Q0torino Y297TAT > TerTAA hepatocytes, but they are rapidly cleared by intracellular Q0cosenza Q305CAA > TerTAA degradation pathways [18]. As Null mutations do not Q0pordenone L327CTG,delT > Ter338TGA induce AAT polymerisation, they confer no risk of liver Q0lampedusa V337GTG,delG > Ter338TGA disease but do confer a particularly high risk of lung Q0dublin F370TTT,delT > Ter373TAA disease [19]. The exact prevalence of Null mutations