Ilaria Ferrarotti

α1-Antitrypsin deficiency

α1-Antitrypsin deficiency (A1ATD) is an inherited disorder caused by mutations in SERPINA1, leading to liver and lung disease. It is not a rare disorder but frequently goes underdiagnosed or misdiagnosed as asthma, chronic obstructive pulmonary disease (COPD) or cryptogenic liver disease. The most frequent disease-associated mutations include the S allele and the Z allele of SERPINA1, which lead to the accumulation of misfolded α1-antitrypsin in hepatocytes, endoplasmic reticulum stress, low circulating levels of α1-antitrypsin and liver disease. Currently, there is no cure for severe liver disease and the only management option is liver transplantation when liver failure is life-threatening. A1ATD-associated lung disease predominately occurs in adults and is caused principally by inadequate protease inhibition. Treatment of A1ATD-associated lung disease includes standard therapies that are also used for the treatment of COPD, in addition to the use of augmentation therapy (that is, infusions of human plasma-derived, purified α1-antitrypsin). New therapies that target the misfolded α1-antitrypsin or attempt to correct the underlying genetic mutation are currently under development.

Laboratory testing of individuals with severe α1-antitrypsin deficiency in three European centres

α1-Antitrypsin (AT) deficiency is a hereditary disorder that may lead to early-onset emphysema, and chronic liver disease later in life. Although there are validated methods for testing, the vast majority of α1-AT-deficient individuals remain undiagnosed. Recommendations have been published for the testing and diagnosis of α1-AT deficiency; however, guidelines on best practice are not well established. In our article, we review the developments in diagnostic techniques that have taken place in recent years, and describe the practices used in our three European centres. The determination of the level of α1-AT and genotyping are reported as the main diagnostic steps, whereas isoelectric focusing (also referred to as phenotyping) is reserved for confirmatory analysis. The following recommendations for best practice are put forward: detection of all PiZZ and other severe deficiency individuals; automated genotyping; preparation of reference standards; quality control programmes; development of standard operating procedure documents; and standardised methods for the collection of dried blood samples. Closer cooperation between laboratories and the sharing of knowledge are recommended, with the objectives of improving the efficiency of the diagnosis of severe α1-AT deficiency, increasing the numbers of individuals who are detected with the disorder, and assisting the establishment of new patient identification programmes.

Serum levels and genotype distribution of α1-antitrypsin in the general population

Rationale α1-Antitrypsin (AAT) deficiency is one of the commonest rare respiratory disorders worldwide. Diagnosis, assessment of risk for developing chronic obstructive pulmonary disease (COPD), and management of replacement therapy require the availability of precise and updated ranges for protein serum levels. Objective This paper aims to provide ranges of serum AAT according to the main genotype classes in the general population. Methods The authors correlated mean AAT serum levels with the main SERPINA1 variants (M1Ala/M1Val (rs6647), M3 (rs1303), M2/M4 (rs709932), S (rs17580) and Z (rs28929474)) in 6057 individuals enrolled in the Swiss Cohort Study on Air Pollution and Lung Diseases in Adults (SAPALDIA) cohort. Results The following ranges (5th–95th percentile) of AAT were found in the serum (g/litre): 1.050–1.640 for PI*MM, 0.880–1.369 for PI*MS, 0.730–1.060 for PI*SS, 0.660–0.997 for PI*MZ and 0.490–0.660 for PI*SZ. There was very little overlap in AAT serum levels between genotype classes generally not believed to confer an enhanced health risk (MM and MS) and those associated with an intermediate AAT deficiency and a potentially mildly enhanced health risk (SS, MZ). Conclusion This work resulted in three important findings: technically updated and narrower serum ranges for AAT according to PI genotype; a suggestion for a population-based ‘protective threshold’ of AAT serum level, used in decision-making for replacement therapy; and more precise ranges framing the intermediate AAT deficiency area, a potential target for future primary prevention.

SERPINA1 Gene Variants in Individuals from the General Population with Reduced α1-Antitrypsin Concentrations

BACKGROUND Individuals with severe deficiency in serum alpha(1)-antitrypsin (AAT) concentrations are at high risk for developing chronic obstructive pulmonary disease (COPD), whereas those carrying the PI*MZ genotype are at slightly increased risk. Testing appropriate subgroups of the population for AAT deficiency (AATD) is therefore an important aspect of COPD prevention and timely treatment. We decided to perform an exhaustive investigation of SERPINA1 gene variants in individuals from the general population with a moderately reduced serum AAT concentration, because such information is currently unavailable. METHODS We determined the Z and S alleles of 1399 individuals enrolled in the Swiss Cohort Study on Air Pollution and Lung Diseases in Adults (SAPALDIA) with serum AAT concentrations < or = 1.13 g/L and submitted 423 of these samples for complete exon 2-->5 sequencing. RESULTS We found that 900 of 1399 samples (64%), carried the normal PI*MM genotype, whereas 499 samples (36%) carried at least 1 SERPINA1 deficiency variant. In the subpopulations in which AAT concentrations ranged from > 1.03 to < or = 1.13 and from > 0.93 to < or = 1.03 g/L, individuals with the PI*MM genotype represented the majority (86.5% and 53.8%, respectively). The PI*MS genotype was predominant (54.9%) in the AAT range of 0.83 to 0.93 g/L, whereas PI*MZ represented 76.4% in the AAT range of > 0.73 to < or = 0.83 g/L. CONCLUSIONS This analysis provided a detailed molecular definition of intermediate AATD, which would be helpful in the diagnostic setting.

Tumour necrosis factor family genes in a phenotype of COPD associated with emphysema

Genetic factors are believed to play a role in the individual susceptibility to chronic obstructive pulmonary disease (COPD). Tumour necrosis factor (TNF) family genes have been widely investigated but inconsistent results may lie either in the genetic heterogeneity of populations or in the poor phenotype definition. A genetic study was performed using a narrower phenotype of COPD. The authors studied 86 healthy smokers and 63 COPD subjects who were enrolled based on irreversible airflow obstruction (forced expiratory volume in one second/forced vital capacity <70% predicted) and a diffusing capacity for carbon monoxide <50% predicted (moderate-to-severe COPD associated with pulmonary emphysema). The following polymorphisms were investigated: TNF-308, the biallelic polymorphism located in the first intron of the lymphotoxin‐α gene, and exon 1 and exon 6 of the TNF receptor 1 and 2 genes, respectively. No significant deviations were found concerning the four polymorphisms studied between the two populations. The authors confirm that the tumour necrosis factor family genes, at least for the polymorphisms investigated, are not major genetic risk factors for chronic obstructive pulmonary disease in Caucasians, either defined in terms of emphysema (this study) or airflow obstruction (previous studies). Nevertheless, the authors would like to emphasise the importance of narrowing the phenotype in the search for genetic risk factors in chronic obstructive pulmonary disease.

Clinical phenotypes of Italian and Spanish patients with α1-antitrypsin deficiency

With the aim of providing better clinical characterisation of patients with &agr;1-antitrypsin deficiency (AATD), we analysed the data of adult patients with severe AATD enrolled in the Spanish and Italian national registries. We assessed 745 subjects, 416 of whom were enrolled in the Spanish registry and 329 in the Italian registry. 57.2% were male and 64.9% were smokers or former smokers with a mean±sd age of 49.9±13.8 years. Most (81.2%) were index cases, mainly having the PI*ZZ genotype (73.4%), and the mean±sd diagnostic delay was 9.0±12.1 years. Patients with chronic bronchitis were younger, had better preserved lung function and lower tobacco consumption. Overlap patients (chronic obstructive pulmonary disease with asthma) were mainly females, more frequently never-smokers and received respiratory medications more often. 48% of emphysema, 27.5% of chronic bronchitis and 44.8% of overlap subjects were receiving augmentation therapy. Compared with PI*ZZ patients (n=547), the PI*SZ (n=124) subjects were older at diagnosis and had more preserved lung function, despite a higher mean smoking consumption. Early diagnosis of AATD is still an unmet need. Augmentation therapy is administered to similar proportions of patients with different clinical phenotypes. PI*ZZ patients in both registries had more severe respiratory disease than those with PI*SZ, despite lower smoking levels.

A Novel Method for Rapid Genotypic Identification of Alpha 1-Antitrypsin Variants

Myotonic dystrophy type 2 (DM2) lacks the expansion on chromosome 19q13 present in DM1 and is characterized by a mutation on 3q21. It has been shown that the DM2 mutation is a huge [CCTG]n repeat expansion in intron 1 of the zinc finger protein 9 (ZNF9) gene. The longest normal allele observed has a ∼30 CCTG repeat, whereas the range of expansion is extremely variable, starting from 75 up to 11,000 CCTGs. Direct analysis by Southern blot, after restriction enzyme digestion of genomic DNA, was the first method chosen for studying the DM2 mutation. However, the expansion size and the elevated grade of somatic instability have limited the sensitivity of the test to approximately 80% of known carriers. We developed a long PCR-formatted protocol, which involves a single genomic in vitro amplification, followed by agarose gel electrophoresis and oligospecific hybridization. We were able to detect normal alleles and expanded ZNF9 alleles, starting from low amounts of genomic DNA (≥1 ng) in virtually all the DM2 patients analyzed, obtaining a molecular detection rate of 100%. This method is quick, sensitive, and reproducible, and it reduces the cost of diagnostic laboratory processing for DM2 diagnosis.

Three New Alpha1-Antitrypsin Deficiency Variants Help to Define a C-Terminal Region Regulating Conformational Change and Polymerization

Alpha1-antitrypsin (AAT) deficiency is a hereditary disorder associated with reduced AAT plasma levels, predisposing adults to pulmonary emphysema. The most common genetic AAT variants found in patients are the mildly deficient S and the severely deficient Z alleles, but several other pathogenic rare alleles have been reported. While the plasma AAT deficiency is a common trait of the disease, only a few AAT variants, including the prototypic Z AAT and some rare variants, form cytotoxic polymers in the endoplasmic reticulum of hepatocytes and predispose to liver disease. Here we report the identification of three new rare AAT variants associated to reduced plasma levels and characterize their molecular behaviour in cellular models. The variants, called Mpisa (Lys259Ile), Etaurisano (Lys368Glu) and Yorzinuovi (Pro391His), showed reduced secretion compared to control M AAT, and accumulated to different extents in the cells as ordered polymeric structures resembling those formed by the Z variant. Structural analysis of the mutations showed that they may facilitate polymerization both by loosening ‘latch’ interactions constraining the AAT reactive loop and through effects on core packing. In conclusion, the new AAT deficiency variants, besides increasing the risk of lung disease, may predispose to liver disease, particularly if associated with the common Z variant. The new mutations cluster structurally, thus defining a region of the AAT molecule critical for regulating its conformational state.

Identification of a novel alpha1-antitrypsin null variant (Q0Cairo).

Alpha1-antitrypsin deficiency (AATD) is a common hereditary disorder associated with high risk of developing pulmonary emphysema early in life and, to a lesser extent, chronic liver disease and cirrhosis. Among Northern Europeans and Northern Americans, more than 95% of individuals with emphysema associated with AATD carry the most frequent AAT deficient gene variants, PI*Z and PI*S. Rare AAT deficient variants account for 2-4% of AATD individuals. We extend the sequence data on AAT by characterizing a novel Null allele detected in 3 subjects: a carrier belonging to an Italian/Egyptian family and 2 members of a family originating from Southern Italy. The mutation raised on a M1 (Ala213) base allele and it is characterized by an A→T transversion at exon III, nt 218, codon 259 (AAA→TAA) (GeneBank accession number AY 256958). The transversion results in a premature stop codon (Lys259AAA→Stop259TAA). The proposed nomenclature of Q0cairo is from the birthplace of the father of first recognized subject. Serum levels and isoelectric focusing of AAT were consistent with the presence of the Null variant.

Severe alpha-1 antitrypsin deficiency in composite heterozygotes inheriting a new splicing mutation QOMadrid

BackgroundSevere Alpha-1 Antitrypsin (AAT) deficiency is a hereditary condition caused by mutations in the SERPINA1 gene, which predisposes to lung emphysema and liver disease. It is usually related to PI*Z alleles, and less frequent to rare and null (QO) alleles. Null-AAT alleles represent the end of a continuum of variants associated with profound AAT deficiency and extremely increased risk of emphysema.MethodsA family with severe AAT deficiency was analyzed to achieve genetic diagnosis. The complete exons and introns of the SERPINA1 gene were sequenced and transcriptional analysis by RT-PCR was performed to characterize the effect of splicing variants found in the patients. In addition, a minigene MGserpa1_ex1b-1c was cloned into the pSAD vector to in vitro investigate the independent impact of variants on splicing process.ResultsWe report a new identified null allele (PI*QOMadrid) in two adult siblings with practically no detectable serum AAT. The PI*QOMadrid allele consist of a duplication of the thymine (T) in position +2 of the donor splice site of exon 1C (+2dupT). In these two subjects, PI*QOMadrid occurred in compound heterozygote combination with the previously described variant PI*QOPorto. Both QOMadrid and QOPorto variants are located very close together in a regulatory region of the SERPINA1 gene. Analysis of transcripts revealed that QOMadrid variant prevented the expression of transcripts from exon 1C, and then normally spliced RNA products are not expected in the liver of these patients. In addition, aberrant splicing patterns of both variants were clearly distinguished and quantified by functional in vitro assays lending further support to their pathogenicity.ConclusionFinding pathogenic mutations in non-coding regions of the SERPINA1 highlight the importance that regulatory regions might have in the disease. Regulatory regions should be seriously considered in discordant cases with severe AAT deficiency where no coding mutations were found.