Familial correlation in the decline of forced expiratory volume in one second

Studies have shown evidence Of significant parent-offspring and sibling cor relation in FEV1, but familial aggregation of decline of FEV1 over time has not been reported. Our study population comprised 392 families enrolled in the Tucson Epidemiological Study of Airway Obstructive Diseases. Subjects were older than 18 yr of age and performed at least 3 pulmonary function te sts over 5 to 20 yr. The slope of FEV1 was calculated for each subject usin g simple linear regression. Multiple regression models were used to compute standardized residual slope values adjusted for possible confounders. Fami lial correlation analysis on residual slope values demonstrated no evidence of spousal or parent-offspring correlation. However, sibling pairs were hi ghly correlated (r = 0.256, p < 0.001, n = 166), especially smoking-concord ant pairs (r = 0.483, p < 0.01 for ever-smokers, and r = 0.280, p < 0.05 fo r never-smokers). The residual slopes of smoking-discordant siblings were n ot significantly correlated (r = 0.031, p < 0.77). Genetic susceptibility t o an accelerated rate of decline associated with smoking may be evidenced i n the increased correlation among smoking sibling pairs, and in the lack of correlation among smoking-discordant sibling pairs. High sibling correlati on in the absence of parent-offspring correlation is compatible with a rece ssive model of inheritance.