LUNG-FUNCTION IN INDIAN TWIN CHILDREN - COMPARISON OF GENETIC VERSUS ENVIRONMENTAL INFLUENCE

The relative contributions of genetic and environmental components in the variability of lung function measurements were studied in 54 twin pairs. Thirty pairs of monozygote (MZ) twins and 24 pairs of dizygotic (DZ) twins were examined. All measurements were made with 9-litre clo sed-circuit-type expirographs using standard spirometric techniques, e xcept for peak expiratory flow rate (PFER) which was recorded with a W right peak flow meter. Within-pair varianaces for inspiratory capacity (IC), vital capacity (VC), forced vital capacity (FVC), forced expira tory volume in 1 second (FEV(1)), forced mid-expiratory flow (FEV(25-7 5%)), forced end-expiratory flow (FEF(75-85%)), maximum expiratory flo w (FEF(200-1200ml)), forced maximum voluntary ventilation (MVV(F)) and PEFR were significantly smaller (p <0.01)in MZ twins than in DZ twins . Tidal volume (V-T), inspiratory reserve volume (IRV), expiratory res erve volume (ERV), forced expiratory volume in 1 second as a percentag e of forced vital capacity (FEV(1%)), and forced expiratory time (FET) were not significantly different. Within-pair correlations were all h igher in MZ than DZ twins. All measurements except for V-T and PEFR sh owed high levels of heritability (23-99%). All measurements were posit ively and significantly correlated with physical characteristics such as weight, standing height, surface area, arm-span, chest circumferenc e and age, except FEV(1%) and FET. Residual values adjusted for physic al characteristics showed similar results to unadjusted values in most cases. These data indicate that major lung function measurements are possibly influenced more by genetic than environmental factors. Geneti cally influenced measurements show higher levels of heritability estim ates and suggest that genetic determination of lung function is possib ly independent of the influence of physical characteristics.