Variability of pulmonary function in alpha-1-antitrypsin deficiency: clinical correlates

Family study of alpha 1-antitrypsin deficiency: effects of cigarette smoking, measured genotype, and their interaction on pulmonary function and biochemical traits

To gain insight into the variable expression of lung disease in alpha 1-antitrypsin (alpha 1AT) deficiency, five quantitative variables including forced expiratory volume at 1 sec (FEV1), forced expiratory flow rate between 25 and 75% of forced vital capacity (FEF25-75), total serum alpha 1AT, oxidized serum alpha 1AT, and total serum immunoglobulin E (IgE) were measured in alpha 1AT deficient individuals and their families. The effect of a known, measured genotype (the Pi type) was estimated for each quantitative trait; the influence of mode of case ascertainment on the measured genotype effect was also assessed. These analyses showed that total alpha 1AT levels are strongly influenced by Pi type; IgE levels are unaffected by Pi type; and FEV1, FEF25-75, and oxidized alpha 1AT are moderately influenced by Pi type. The effect of genotype-by-environment interaction between Pi type and pack-years of cigarette smoking on the five quantitative phenotypes was studied using an analysis of covariance. Significant Pi x pack-years interaction was evident for FEV1, but this effect is confounded in this data set with the Pi x age interaction. Probands who were ascertained because they had chronic obstructive pulmonary disease (COPD) do not demonstrate the significant Pi x pack-years interaction effect of the Pi x pack-years subjects ascertained for other reasons demonstrate. The effect of the Pi x pack-years interaction on FEV1 was no longer significant on a transformed scale, (FEVf12,) thus providing an additive scale for future data analysis. The increased sensitivity of Pi MZ individuals in our sample to cigarette smoking reduced the Pi x packs-years interaction effect on FEF25-75 to borderline significance. This investigation has provided an opportunity to incorporate both measured genotype and genotype-by-environment interaction analyses into the study of the variable expression of lung disease in Pi Z individuals.

What lies ahead? Future research and treatment for chronic obstructive pulmonary disease

The morphologic basis for airflow obstruction in chronic obstructive pulmonary disease is extremely complex and consists of heterogeneous lesions. Emphysema seems to be the single most important lesion in this disorder. Abnormalities of the peripheral conducting airways, including inflammation, fibrosis, smooth muscle hypertrophy, and hyperplasia of mucus-secreting elements, are also of functional importance. Low-grade inflammation involving both airways and parenchyma occurs after only short-term exposure to cigarette smoke. This chronic inflammatory reaction may initiate other, largely irreversible, tissue responses that are responsible for airflow function. In the case of emphysema, tissue obstruction is thought to be due to an elastase-antielastase imbalance, leading to accelerated destruction of elastic fibers in the alveolar walls. Logical strategies for controlling the development of emphysema might include measures to prevent the influx of phagocyte-borne elastases into the lung as well as efforts to supplement the antiprotease shield of the lower airways. Anti-inflammatory drugs might also be effective in suppressing cigarette-smoke-induced reactions in the conducting airways. Other agents might be effective by preventing bronchoconstriction and the proliferation of smooth muscle elements in airway walls.