Risk factors for obstructive lung disease

"What are my chances of developing COPD if one of my parents has the disease?" A systematic review and meta-analysis of prevalence of co-occurrence of COPD diagnosis in parents and offspring

Introduction

Intergenerational associations in chronic obstructive pulmonary disease (COPD) have been well recognized and may result from genetic, gene environment, or exposure to life course factors. Consequently, adult offspring of parents with COPD may be at a greater risk of developing COPD. The aim of this study was to review the prevalence of co-occurrence of COPD in adult offspring with one or both parents having COPD independent of specific genetic variations.

Methods

In total, five databases were searched for original studies in which prevalence of COPD was reported in both offspring (children) and one or both parents. Studies were excluded if COPD was not clearly defined, COPD was linked to specific genetic variations, COPD was combined with other chronic respiratory conditions, or estimates included other first-degree relatives. Data extraction (ie, sample characteristics, prevalence of COPD, and odds ratio [OR] if reported) was completed by two independent reviewers. A meta-analysis of prevalence and OR was conducted, where possible.

Results

Of the 3,382 citations, 129 full texts were reviewed to include eight studies (six case–control, one cross-sectional, and one cohort) reflecting either prevalence of COPD in offspring of parents with COPD (descendent approach, n=3), which ranged from 0% to 17.3%, or prevalence of people with COPD reporting positive parental history of COPD (antecedent approach, n=5), for which the pooled prevalence was 28.6%. Offspring of people with COPD had 1.57 times greater odds (95% confidence interval =1.29–1.93; P<0.001) of having COPD compared with people not having a parental history of COPD.

Conclusion

The prevalence of COPD in adult offspring of people with COPD is greater than population-based estimates, and the ORs indicate a higher risk in this group. This offers clinicians a potential strategy for opportunistic screening, early identification, and intervention in this at-risk group.

Systematic review of the evidence relating FEV1 decline to giving up smoking

BACKGROUND

The rate of forced expiratory volume in 1 second (FEV1) decline ("beta") is a marker of chronic obstructive pulmonary disease risk. The reduction in beta after quitting smoking is an upper limit for the reduction achievable from switching to novel nicotine delivery products. We review available evidence to estimate this reduction and quantify the relationship of smoking to beta.

METHODS

Studies were identified, in healthy individuals or patients with respiratory disease, that provided data on beta over at least 2 years of follow-up, separately for those who gave up smoking and other smoking groups. Publications to June 2010 were considered. Independent beta estimates were derived for four main smoking groups: never smokers, ex-smokers (before baseline), quitters (during follow-up) and continuing smokers. Unweighted and inverse variance-weighted regression analyses compared betas in the smoking groups, and in continuing smokers by amount smoked, and estimated whether beta or beta differences between smoking groups varied by age, sex and other factors.

RESULTS

Forty-seven studies had relevant data, 28 for both sexes and 19 for males. Sixteen studies started before 1970. Mean follow-up was 11 years. On the basis of weighted analysis of 303 betas for the four smoking groups, never smokers had a beta 10.8 mL/yr (95% confidence interval (CI), 8.9 to 12.8) less than continuing smokers. Betas for ex-smokers were 12.4 mL/yr (95% CI, 10.1 to 14.7) less than for continuing smokers, and for quitters, 8.5 mL/yr (95% CI, 5.6 to 11.4) less. These betas were similar to that for never smokers. In continuing smokers, beta increased 0.33 mL/yr per cigarette/day. Beta differences between continuing smokers and those who gave up were greater in patients with respiratory disease or with reduced baseline lung function, but were not clearly related to age or sex.

CONCLUSION

The available data have numerous limitations, but clearly show that continuing smokers have a beta that is dose-related and over 10 mL/yr greater than in never smokers, ex-smokers or quitters. The greater decline in those with respiratory disease or reduced lung function is consistent with some smokers having a more rapid rate of FEV1 decline. These results help in designing studies comparing continuing smokers of conventional cigarettes and switchers to novel products.

Chronic obstructive pulmonary disease in alpha1-antitrypsin PI MZ heterozygotes: a meta-analysis

BACKGROUND

Severe alpha(1)-antitrypsin deficiency, usually related to homozygosity for the protease inhibitor (PI) Z allele, is a proven genetic risk factor for chronic obstructive pulmonary disease (COPD). The risk of COPD in PI MZ heterozygous individuals is controversial.

METHODS

A search of MEDLINE from January 1966 to May 2003 identified studies that examined the risk of COPD in PI MZ individuals and studies that measured forced expiratory volume in 1 second (FEV(1)) in heterozygotes.

RESULTS

In 16 studies that reported COPD as a categorical outcome, the combined odds ratio (OR) for PI MZ versus PI MM (normal genotype) was 2.31 (95% CI 1.60 to 3.35). The summary OR was higher in case-control studies (OR 2.97; 95% CI 2.08 to 4.26) than in cross sectional studies (OR 1.50; 95% CI 0.97 to 2.31) and was attenuated in studies that adjusted for cigarette smoking (OR 1.61; 95% CI 0.92 to 2.81). In seven studies that reported FEV(1) as a continuous outcome there was no difference in mean FEV(1) between PI MM and PI MZ individuals.

CONCLUSIONS

Case-control studies showed increased odds of COPD in PI MZ individuals, but this finding was not confirmed in cross sectional studies. Variability in study design and quality limits the interpretation. These results are consistent with a small increase in risk of COPD in all PI MZ individuals or a larger risk in a subset. Future studies that adjust for smoking and include other COPD related phenotypes are required to conclusively determine the risk of COPD in PI MZ heterozygotes.