Direct and indirect effects of Growth Hormone Deficiency (GHD) on lung function in children: A mediation analysis

Background: Studies on pulmonary function tests (PFTs) in Growth Hormone Deficiency (GHD) children are lacking. The aims of this study were: (i) to investigate PFTs in GHD pre-pubertal children with respect to Controls, before starting Growth Hormone Therapy (GHT) (T0); (ii) to evaluate changes of PFTs in GHD vs Controls, after 1-year GHT (T1). For both aims the mediation analysis (MA) was applied to evaluate the extent to which the relationship between GHD and PFTs could be ascribed to a height-mediated (indirect) or a GH direct effect. Methods: 47 pre-pubertal GHD children (aged 5-14 years) underwent PFTs at T0 and T1. At T0, 47 healthy children matched for age and sex were enrolled as Controls. A MA was performed to assess the relationship between GHD and PFTs and height. Statistical analyses were performed using the statistical software R (https:// cran.r-project.org/mirrors.html). A p-value<0.05 was considered significant. Measurements and main results: At T0, PFTs indices were significantly lower in GHD than in Controls. From T0 to T1 a significant improvement was found in PFTs. The percentages of the mediated effect on FVC, FEV1, FEF25-75% and TLC were<50% at T0, suggesting that the direct effect was prevalent. At T1, the percentages of the mediated effect for spirometry indices were >=50%, indicating that the indirect (height-mediated) effect was the most relevant. Conclusions: The study shows that pre-pubertal children with GHD have an impairment of lung function not exclusively attributable to the indirect (height-mediated) effect, but also to the direct GH action which is mitigated after 1-year of GHT.