Alpha1-Antitrypsin as a Risk for Infant and Adult Respiratory Outcomes in a National Birth Cohort

SERPINA1 gene polymorphisms in a population-based ALSPAC cohort

BACKGROUND

There is an association between persistent preschool wheezing phenotypes and school-age asthma. These wheezing/asthma phenotypes likely represent clinical entities having specific genetic risk factors. The SERPINA1 gene encodes α ₁ -antitrypsin (AAT), and mutations in the gene are important in the pathophysiology of pulmonary diseases. We hypothesized that there might be an association between SERPINA1 gene polymorphisms and the risk of developing wheezing/school age asthma.

OBJECTIVE

To examine 10 single nucleotide polymorphisms (SNPs) of SERPINA1 (rs6647, rs11832, rs17580, rs709932, rs1243160, rs2854254, rs8004738, rs17751769, rs28929470, and rs28929474) and relate them to childhood wheezing phenotypes and doctor-diagnosed asthma in the population-based Avon Longitudinal Study of Parents and Children (ALSPAC) cohort.

METHODS

Wheeze data, reports of physician-diagnosed asthma and data on the SERPINA1 gene SNPs, were available for 7964 children. Binary logistic regression was used to assess the associations between allele prevalence and wheezing and asthma phenotypes. P values were adjusted to account for multiple hypotheses using the Benjamini-Hochberg false discovery rate.

RESULTS

Only within a subgroup of children with asthma who had no prior diagnosis of preschool wheeze was there a trend for association between rs28929474 (Glu342Lys, Pi*Z causing AAT deficiency; P = .0058, adjusted P = .058). No SNP was associated with wheezing and asthma in those with preschool wheeze.

CONCLUSION

Analyzed SNPs in SERPINA1 are not associated with wheezing/asthma phenotypes. Only rs28929474, the most common pathologic SNP (Pi*Z) in the SERPINA1 gene, might be associated with a risk of developing school-age asthma without exhibiting preschool wheeze.

A study of common Mendelian disease carriers across ageing British cohorts: meta-analyses reveal heterozygosity for alpha 1-antitrypsin deficiency increases respiratory capacity and height

BACKGROUND

Several recessive Mendelian disorders are common in Europeans, including cystic fibrosis (CFTR), medium-chain-acyl-Co-A-dehydrogenase deficiency (ACADM), phenylketonuria (PAH) and alpha 1-antitrypsin deficiency (SERPINA1).

METHODS

In a multicohort study of >19,000 older individuals, we investigated the relevant phenotypes in heterozygotes for these genes: lung function (forced expiratory volume in 1 second (FEV1), forced vital capacity (FVC)) for CFTR and SERPINA1; cognitive measures for ACADM and PAH; and physical capability for ACADM, PAH and SERPINA1.

RESULTS

Findings were mostly negative but lung function in SERPINA1 (protease inhibitor (PI) Z allele, rs28929474) showed enhanced FEV1 and FVC (0.13 z-score increase in FEV1 (p=1.7 × 10(-5)) and 0.16 z-score increase in FVC (p=5.2 × 10(-8))) in PI-MZ individuals. Height adjustment (a known, strong correlate of FEV1 and FVC) revealed strong positive height associations of the Z allele (1.50 cm increase in height (p=3.6 × 10(-10))).

CONCLUSIONS

The PI-MZ rare (2%) SNP effect is nearly four times greater than the 'top' common height SNP in HMGA2. However, height only partially attenuates the SERPINA1-FEV1 or FVC association (around 50%) and vice versa. Height SNP variants have recently been shown to be positively selected collectively in North versus South Europeans, while the Z allele high frequency is localised to North Europe. Although PI-ZZ is clinically disadvantageous to lung function, PI-MZ increases both height and respiratory function; potentially a balanced polymorphism. Partial blockade of PI could conceivably form part of a future poly-therapeutic approach in very short children. The notion that elastase inhibition should benefit patients with chronic obstructive pulmonary disease may also merit re-evaluation. PI is already a therapeutic target: our findings invite a reconsideration of the optimum level in respiratory care and novel pathway potential for development of agents for the management of growth disorders.

SERPINA1 PiZ and PiS heterozygotes and lung function decline in the SAPALDIA cohort

Background

Severe alpha1-antitrypsin (AAT) deficiency is a strong risk factor for COPD. But the impact of gene variants resulting in mild or intermediate AAT deficiency on the longitudinal course of respiratory health remains controversial. There is indication from experimental studies that pro-inflammatory agents like cigarette smoke can interact with these variants and thus increase the risk of adverse respiratory health effects. Therefore, we tested the effect of the presence of a protease inhibitor (Pi) S or Z allele (PiMS and PiMZ) on the change in lung function in different inflammation-exposed subgroups of a large, population-based cohort study.

Methodology and Principal Findings

The SAPALDIA population includes over 4600 subjects from whom SERPINA1 genotypes for S and Z alleles, spirometry and respiratory symptoms at baseline and after 11 years follow-up, as well as proxies for inflammatory conditions, such as detailed smoking history, obesity and high sensitivity C-reactive protein (hs-CRP), were available. All analyses were performed by applying multivariate regression models. There was no overall unfavourable effect of PiMS or PiMZ genotype on lung function change. We found indication that PiZ heterozygosity interacted with inflammatory stimuli leading to an accelerated decline in measures in use as indices for assessing mild airway obstruction. Obese individuals with genotype PiMM had an average annual decline in the forced mid expiratory flow (ΔFEF25-75%) of 58.4 ml whereas in obese individuals with PiMZ it amounted to 92.2 ml (p = 0.03). Corresponding numbers for persistent smokers differed even more strongly (66.8 ml (PiMM) vs. 108.2 ml (PiMZ), p = 0.005). Equivalent, but less strong associations were observed for the change in the FEV1/FVC ratio.

Conclusions

We suggest that, in addition to the well established impact of the rare PiZZ genotype, one Z allele may be sufficient to accelerate lung function decline in population subgroups characterized by elevated levels of low grade inflammation.

Asthma and COPD in alpha-1 antitrypsin deficiency. Evidence for the Dutch hypothesis

This review summarizes the current information on the relationship between severe alpha-1 antitrypsin deficiency (AATD), asthma and COPD. AATD is a genetic predisposition to the development of early COPD in susceptible individuals and reduction in known factors that enhance lung function loss is the paramount aim of management. Asthma is one controllable condition that leads to the accelerated decline in lung function. Current literature indicates that asthma signs and symptoms are common in those AATD with or without COPD and that bronchodilator response is a risk factor for FEV(1) decline. Furthermore AATD itself predisposes to airway hyper responsiveness, an essential ingredient for reversible airflow obstruction. In the absence of well-characterized markers to distinguish COPD from asthma, clinical diagnosis leads to a delay in the recognition that asthma symptoms such as wheezing can be an early manifestation of COPD in AATD. In addition failure to appreciate asthma overlap in AATD may lead to inadequate suppression of airway inflammation leading to the development of airflow obstruction. The implications of this are discussed as are potential approaches and recommendations for treatment.

MUC7 haplotype analysis: results from a longitudinal birth cohort support protective effect of the MUC7*5 allele on respiratory function

The mucin MUC7 is a glycoprotein that plays a role in bacterial clearance and has candidacidal activity. There are two common allelic forms with 5 or 6 tandem repeats (TR) of a 23 amino acid motif within the highly glycosylated (mucin) domain. The MUC7*5 allele has previously been shown to be less prevalent in patients with asthma, suggesting a protective role in respiratory function. Here we report the characterisation of other frequent genetic variation within and in the vicinity of the gene MUC7. A total of 26 polymorphisms were identified of which 5 are located in transcribed regions. A subset of 8 polymorphisms was selected to represent the major haplotypes, and allelic association was studied in individuals of Northern European ancestry, including known asthmatics. There was low haplotype diversity and strong association between each of the loci, and the MUC7*5 allele-carrying haplotype remained the one most strongly associated with asthma. Five of these polymorphisms have also been tested in the 1946 longitudinal birth cohort, for whom developmental, environmental and respiratory health data are available. We show that the haplotype carrying MUC7*5 is associated with higher FEV1 at 53 years, reduced age-related decline of FEV1, and also reduced incidence of wheeze.

Smoking and the incidence of asthma during adolescence: results of a large cohort study in Germany

BACKGROUND

The association between smoking and asthma or wheeze has been extensively studied in cross sectional studies, but evidence from large prospective cohort studies on the incidence of asthma during adolescence is scarce.

METHODS

We report data from a cohort study in two German cities, Dresden and Munich. The study population (n = 2936) was first studied in 1995/6 at age 9-11 years as part of phase II of the International Study of Asthma and Allergies in Childhood (ISAAC II) and followed up in 2002/3. At baseline the parents completed a questionnaire and children underwent clinical examination and blood sampling. At follow up the young adults completed questionnaires on respiratory health, living, and exposure conditions. Incidence risk ratios (IRR) were calculated and adjusted for potential confounders using a modified Poisson regression approach.

RESULTS

The adjusted IRR for incident wheeze for active smokers compared with non-smokers was 2.30 (95% confidence interval (CI) 1.88 to 2.82). The adjusted IRR was slightly higher for incident wheeze without a cold (2.76, 95% CI 1.99 to 3.84) and the incidence of diagnosed asthma (2.56, 95% CI 1.55 to 4.21). Analysis of duration and intensity of active smoking indicated dose dependent associations. Stratified analyses showed that the risk of incident wheeze without a cold in atopic smokers increased with decreasing plasma alpha(1)-antitrypsin levels at baseline (1.64, 95% CI 1.22 to 2.20 per interquartile range).

CONCLUSIONS

Active smoking is an important risk factor for the incidence of asthma during adolescence. Relatively lower plasma levels of alpha(1)-antitrypsin, although well above currently accepted thresholds, may increase susceptibility to respiratory disease among atopic smokers.