SERPINA1 Full-Gene Sequencing Identifies Rare Mutations Not Detected in Targeted Mutation Analysis

Alpha-1-Antitrypsin Deficiency Targeted Testing and Augmentation Therapy: A Canadian Thoracic Society Meta-Analysis and Clinical Practice Guideline

Alpha-1-antitrypsin (A1AT) deficiency is a common hereditary disorder associated with increased risk of developing chronic obstructive pulmonary disease (COPD). Many individuals with severe A1AT deficiency go undiagnosed, or are diagnosed late, and fail to benefit from disease-specific counseling and modifying care. Since the 2012 Canadian Thoracic Society (CTS) A1AT deficiency clinical practice guideline, new approaches to optimal diagnosis using modern genetic testing and studies of A1AT augmentation therapy have been published. We performed a systematic review and meta-analysis, which along with expert clinical input, informed recommendations. We conditionally recommend testing for A1AT deficiency in all individuals with COPD at the time of diagnosis, individuals with adult-onset asthma with persistent airway obstruction, and individuals with unexplained bronchiectasis. We suggest genetic testing with DNA sequencing of SERPINA1 gene as the initial test for individuals with high clinical suspicion for A1AT deficiency, and initial measurement of serum A1AT levels in individuals with moderate clinical suspicion of A1AT deficiency, followed by genetic testing with DNA sequencing of SERPINA1 gene if A1AT level is <23 μmol/L (<1.2 g/L). Following identification of an abnormal gene for A1AT in individuals, whether heterozygote or homozygote, we suggest first-degree relatives be provided genetic counseling and offered testing for A1AT deficiency. The panel conditionally recommends A1AT augmentation therapy to patients who do not smoke or who formerly smoked with COPD (forced expiratory volume in 1 s [FEV1] < 80% predicted; associated with emphysema), with documented deficiency genotypes and severely reduced A1AT level (< 11 μmol/L or < 0.57 g/L) in addition to receiving optimal pharmacological and nonpharmacological therapies for COPD.

Computational Tools to Assist in Analyzing Effects of the SERPINA1 Gene Variation on Alpha-1 Antitrypsin (AAT)

In the rapidly advancing field of bioinformatics, the development and application of computational tools to predict the effects of single nucleotide variants (SNVs) are shedding light on the molecular mechanisms underlying disorders. Also, they hold promise for guiding therapeutic interventions and personalized medicine strategies in the future. A comprehensive understanding of the impact of SNVs in the SERPINA1 gene on alpha-1 antitrypsin (AAT) protein structure and function requires integrating bioinformatic approaches. Here, we provide a guide for clinicians to navigate through the field of computational analyses which can be applied to describe a novel genetic variant. Predicting the clinical significance of SERPINA1 variation allows clinicians to tailor treatment options for individuals with alpha-1 antitrypsin deficiency (AATD) and related conditions, ultimately improving the patient's outcome and quality of life. This paper explores the various bioinformatic methodologies and cutting-edge approaches dedicated to the assessment of molecular variants of genes and their product proteins using SERPINA1 and AAT as an example.

Alpha1-antitrypsin deficiency: An updated review

Alpha1-antitrypsin deficiency (AATD) is a rare autosomal recessive disease associated with the homozygous Z variant of the SERPINA1 gene. Clinical expression of AATD, reported 60 years ago associate a severe deficiency, pulmonary emphysema and/or liver fibrosis. Pulmonary emphysema is due to the severe alpha1-antitrypsin deficiency of the ZZ homozygous status and is favored by smoking. Liver fibrosis is due to the ZZ homozygous status and is favored by obesity and excessive chronic alcohol intake, with a risk of liver cancer. Diagnosis is based on serum level and either isoelectric focusing determination of the biochemical phenotype or PCR detection of some variants. SERPINA1 gene sequencing is necessary in case of discrepancies between the results of these tests. No treatment is available for the liver disease in AATD. Although no specific trial has been performed, COPD in AATD should be treated as per COPD recommendations. Based on a randomized clinical trial, augmentation therapy is indicated in non-smoking adults less than 70 years of age with emphysema at chest CT, confirmed homozygous AATD, and FEV1 between 35% and 70% of predicted. In contrast Z heterozygosis (MZ or SZ) brings a risk of lung or liver disease only in association with further risk factors. Early detection, in all patients with COPD and chronic liver disease, is critical for the correct information of Z variant carriers. News ways of correcting the liver production of alpha1-antitrypsin will modify the care of AATD patients.

Characterization of three new SERPINA1 variants PiQ0Heidelberg II, PiQ0Heidelberg III and PiQ0Heidelberg IV in patients with severe alpha-1 antitrypsin deficiency

Background

The clinical and molecular characteristics of three patients with previously unreported SERPINA1 mutations associated with severe alpha-1 antitrypsin deficiency (AATD) are described. The pathophysiology of the chronic obstructive pulmonary disease (COPD) present in these patients was characterized through clinical, biochemical, and genetic examinations.

Case presentations

Case 1: A 73-year-old male with bilateral centri-to panlobular emphysema and multiple increasing ventrobasal bullae and incomplete fissures, COPD (Global Initiative for Chronic Obstructive Lung Disease (GOLD) grade III B), progressive dyspnea on exertion (DOE), AAT level of 0.1-0.2 g/L. Genetic testing revealed a unique SERPINA1 mutation: Pi*Z/c.1072C > T. This allele was designated PiQ0_{Heidelberg II}. Case 2: A 47-year-old male with severely heterogenous centri-to panlobular emphysema concentrated in the lower lobes, COPD GOLD IV D with progressive DOE, AAT <0.1 g/L. He also had a unique Pi*Z/c.10del mutation in SERPINA1. This allele was named PiQ0_{Heidelberg III}. Case 3: A 58-year-old female with basally accentuated panlobular emphysema, GOLD II B COPD, progressive DOE. AAT 0.1 g/L. Genetic analysis revealed Pi*Z/c.-5+1G > A and c.-472G > A mutations in SERPINA1. This variant allele was named PiQ0_{Heidelberg IV}.

Conclusions

Each of these patients had a unique and previously unreported SERPINA1 mutation. In two cases, AATD and a history of smoking led to severe lung disease. In the third case, timely diagnosis, and institution of AAT replacement stabilized lung function. Wider screening of COPD patients for AATD could lead to faster diagnosis and earlier treatment of AATD patients with AATD which could slow or prevent progression of their disease.

Clinical characterization of a novel alpha1-antitrypsin null variant: PiQ0Heidelberg

The clinical characterization of a null variant of SERPINA1 - PiQ0Heidelberg - resulting in alpha1-antitrypsin (AAT) deficiency is described. This rare mutation (c.-5+5 G > A) has been previously identified but not clinically described. The 77 year-old female patient had GOLD-3, Group B COPD, severe destructive panlobular emphysema and newly observed respiratory failure on exertion at the time the genetic analysis was performed. Serum AAT level was 0.1 g/L (reference 0.9-2.0 g/L). Isoelectric focusing showed only the Z-protein indicating that this was a null mutation. The patient has started AAT replacement. Early screening and identification of AAT deficiency would allow for earlier intervention.

Liquid Chromatography-Tandem Mass Spectrometry-Based α1-Antitrypsin (AAT) Testing

OBJECTIVES

Failure to produce sufficient quantities of functional α1-antitrypsin (AAT) can result in AAT deficiency (AATD) and significant comorbidities. Laboratory testing plays a vital role in AATD, with diagnosis requiring documentation of both a low AAT level and a mutated allele. This retrospective evaluation examines the efficacy of a liquid chromatography-tandem mass spectrometry (LC-MS/MS) (proteotyping)-based algorithm for AATD detection.

METHODS

A 16-month retrospective data analysis was performed on two cohorts: 5,474 samples tested with the proteotype-based algorithm and 16,147 samples directly tested by isoelectric focusing (IEF) phenotyping.

RESULTS

LC-MS/MS reduced the rate of IEF testing by 97%. The 3% of cases reflexed to IEF resulted in 12 (0.2%) additional phenotype findings. Retrospectively applying the proteotype-based algorithm to the IEF cohort demonstrated a 99.9% sensitivity for the detection of deficiency-associated phenotypes. Most deficiency phenotypes missed by the proteotyping algorithm would come from heterozygous patients with an F, I, or P paired to an S or Z. In all of these cases, patient AAT levels were greater than 70 mg/dL, above the threshold for AAT augmentation therapy.

CONCLUSIONS

The proteotype algorithm is a sensitive and cost-effective approach for the diagnosis of clinical AAT deficiency.

Granularity of SERPINA1 alleles by DNA sequencing in CanCOLD

DNA sequencing of the SERPINA1 gene to detect α₁-antitrypsin (AAT) deficiency (AATD) may provide a better appreciation of the individual and cumulative impact of genetic variants on AAT serum levels and COPD phenotypes.AAT serum level and DNA sequencing of the coding regions of SERPINA1 were performed in 1359 participants of the Canadian Cohort Obstructive Lung Disease (CanCOLD) study. Clinical assessment for COPD included questionnaires, pulmonary function testing and computed tomography (CT) imaging. Phenotypes were tested for association with SERPINA1 genotypes collated into four groups: normal (MM), mild (MS and MI), intermediate (heterozygote MZ, non-S/non-Z/non-I, compound IS, and homozygote SS) and severe (ZZ and SZ) deficiency. Smoking strata and MZ-only analyses were also performed.34 genetic variants were identified including 25 missense mutations. Overall, 8.1% of alleles in this Canadian cohort were deficient and 15.5% of 1359 individuals were carriers of at least one deficient allele. Four AATD subjects were identified and had statistically lower diffusion capacity and greater CT-based emphysema. No COPD phenotypes were associated with mild and intermediate AATD in the overall cohort or stratified by smoking status. MZ heterozygotes had similar CT-based emphysema, but lowered diffusion capacity compared with normal and mild deficiency.In this Canadian population-based cohort, comprehensive genetic testing for AATD reveals a variety of deficient alleles affecting 15.5% of subjects. COPD phenotype was demonstrated in severe deficiency and MZ heterozygotes. This study shows the feasibility of implementing a diagnostic test for AATD using DNA sequencing in a large cohort.

Liver Involvement in Children with Alpha-1 Antitrypsin Deficiency: A Multicenter Study

PURPOSE

Alpha-1 antitrypsin deficiency (A1ATD) in one of the most common genetic causes of liver disease in children. We aimed to analyze the clinical characteristics and outcomes of patients with A1ATD.

METHODS

This study included patients with A1ATD from five pediatric hepatology units. Demographics, clinical findings, genetics, and outcome of the patients were recorded (n=25).

RESULTS

Eight patients (32.0%) had homozygous PiZZ genotype while 17 (68.0%) had heterozygous genotype. Patients with PiZZ genotype had lower alpha-1 antitrypsin levels than patients with PiMZ genotype (37.6±7.7 mg/dL vs. 66.5±22.7 mg/dL, p=0.0001). Patients with PiZZ genotype were diagnosed earlier than patients with PiMZ genotype, but this was not significant (13±6.8 months vs. 23.7±30.1 months, p=0.192). Follow-up revealed the death of one patient (12.5%) with a homozygous mutation, and revealed that one patient had child A cirrhosis, five patients (62.5%) had chronic hepatitis, and one patient (12.5%) was asymptomatic. Nine of the 17 patients with a heterozygous mutation had chronic hepatitis (52.9%), two (11.7%) had child A cirrhosis, and six (35.2%) were asymptomatic. Overall, 18 (72%) of the 25 children had liver pathology in the long-term.

CONCLUSION

Although prevalence is rare, patients with liver disorders should be checked for alpha-1 antitrypsin levels. Moreover, long-term follow-up is essential because most patients have a liver pathology.

New Patient-Centric Approaches to the Management of Alpha-1 Antitrypsin Deficiency

Alpha-1 antitrypsin deficiency (AATD) is a rare and underdiagnosed genetic predisposition for COPD and emphysema and other conditions, including liver disease. Although there have been improvements in terms of awareness of AATD and understanding of its treatment in recent years, current challenges center on optimizing detection and management of patients with AATD, and improving access to intravenous (IV) AAT therapy – the only available pharmacological intervention that can slow disease progression. However, as an orphan disease with geographically dispersed patients, international cooperation is essential to address these issues. To achieve this, new European initiatives in the form of the European Reference Network for Rare Lung Diseases (ERN-LUNG) and the European Alpha-1 Research Collaboration (EARCO) have been established. These organizations are striving to address the current challenges in AATD, and provide a new platform for future research efforts in AATD. The first objectives of ERN-LUNG are to establish a quality control program for European AATD laboratories and create a disease management program for AATD, following the success of such programs in the United States. The main purpose of EARCO is to create a pan-European registry, with the aim of understanding the natural history of the disease and supporting the development of new treatment modalities in AATD and access to AAT therapy. Going further, other patient-centric initiatives involve improving the convenience of intravenous AAT therapy infusions through extended-interval dosing and self-administration. The present review will discuss the implementation of these initiatives and their potential contribution to the optimization of patient care in AATD.

Protein modeling to assess the pathogenicity of rare variants of SERPINA1 in patients suspected of having Alpha 1 Antitrypsin Deficiency

Background

Alpha 1 Antitrypsin (AAT) is a key serum proteinase inhibitor encoded by SERPINA1. Sequence variants of the gene can cause Alpha 1 Antitrypsin Deficiency (AATD), a condition associated with lung and liver disease. The majority of AATD cases are caused by the ‘Z’ and ‘S’ variants – single-nucleotide variations (SNVs) that result in amino acid substitutions of E342K and E264V. However, SERPINA1 is highly polymorphic, with numerous potentially clinically relevant variants reported. Novel variants continue to be discovered, and without reports of pathogenicity, it can be difficult for clinicians to determine the best course of treatment.

Methods

We assessed the utility of next-generation sequencing (NGS) and predictive computational analysis to guide the diagnosis of patients suspected of having AATD. Blood samples on serum separator cards were submitted to the DNA₁ Advanced Screening Program (Biocerna LLC, Fulton, Maryland, USA) by physicians whose patients were suspected of having AATD. Laboratory analyses included quantification of serum AAT levels, qualitative analysis by isoelectric focusing, and targeted genotyping and NGS of the SERPINA1 gene. Molecular modeling software UCSF Chimera (University College of San Francisco, CA) was used to visualize the positions of amino acid changes as a result of rare/novel SNVs. Predictive software was used to assess the potential pathogenicity of these variants; methods included a support vector machine (SVM) program, PolyPhen-2 (Harvard University, Cambridge, MA), and FoldX (Centre for Genomic Regulation, Barcelona, Spain).

Results

Samples from 23 patients were analyzed; 21 rare/novel sequence variants were identified by NGS, including splice variants (n = 2), base pair deletions (n = 1), stop codon insertions (n = 2), and SNVs (n = 16). Computational modeling of protein structures caused by the novel SNVs showed that 8 were probably deleterious, and two were possibly deleterious. For the majority of probably/possibly deleterious SNVs (I50N, P289S, M385T, M221T, D341V, V210E, P369H, V333M and A142D), the mechanism is probably via disruption of the packed hydrophobic core of AAT. Several deleterious variants occurred in combination with more common deficiency alleles, resulting in very low AAT levels.

Conclusions

NGS and computational modeling are useful tools that can facilitate earlier, more precise diagnosis, and consideration for AAT therapy in AATD.

Electronic supplementary material

The online version of this article (10.1186/s12881-019-0852-5) contains supplementary material, which is available to authorized users.