Quantitative genetic model
Figure 2 and Table 3 presents the correlation between asthma and
FENO separated into genetic and environmental sources.
These were factors uniquely related to allergen-specific IgE level,
factors unique to eosinophils, factors shared by allergen-specific IgE
level and eosinophils, and factors shared between asthma and
FENO, as estimated in the (best-fitting) AE model
(Online Supplemental method outlines how the separation into unique and
shared sources has been achieved).
In the best-fitting AE model, a significant phenotypic correlation,
rph, was noted between asthma and FENO(rph = 0.19; Table 3). The part of the phenotypic
correlation, which can be attributable to additive genetic effects,
rph-a, due to allergen-specific IgE level was
statistically significant (rph-a = 0.10) and accounted
for half (54%) of the correlation between asthma and
FENO. All other estimates were non-significant.
Other quantitative genetic models (ACE, ADE and CE), the path
coefficients from the AE model, as well as the heritability estimates,
are shown in Online Data Supplement, ETable 3, ETable 4A-B.
Twin correlations and results from the quantitative genetic models
obtained when the categorical variable IgE positive was used instead of
allergen-specific IgE level can be found in the Online Supplemental
material, ETables 5–6. Overall, the results using the categorical IgE
positive were very similar to the results obtained from the continuous
allergen-specific IgE level.