Chagas disease (CD) is one of the most devasting parasitic diseases in the Americas affecting 7 to 8 million people worldwide. In vitro and in vivo experiments have demonstrated that decreased growth hormone (GH) serum levels occur as CD progresses. Interestingly, inactivating mutations in the GH receptor in humans induce Laron syndrome (LS), a clinical entity characterized by increased GH and decreased insulin growth factor-1 (IGF-1) serum levels. The largest cohort of LS subjects lives in the southern provinces of Ecuador. Remarkably, CD prevalence in these individuals is diminished despite living in highly endemic areas. In the current ex vivo study, we employed serum from GHR -/- mice, also known as LS mice (a model of GH resistance with high GH and low IGF-1 levels), and serum from bovine GH (bGH) transgenic mice (high GH and IGF-1), to test the effect on T. cruzi infection. We infected mouse fibroblast L-cells treated with serum from each type of mouse with metacyclic trypomastigotes from Trypanosoma cruzi (etiological CD infectious agent). Treatment with GHR-/- serum (LS mice) significantly decreased infection by 28% compared to 48% seen in control wild-type mouse serum (WT). Treatment with bGH mouse serum significantly decreased infection by only 41% compared to 54% from WT controls. Our results suggest that high GH and low IGF-1 in blood circulation, as typically seen in LS individuals, confers partial protection against T. cruzi infection.

Growth hormone (GH) is a peptide hormone that plays a crucial role in controlling growth, development, and lifespan. Molecular regulation of GH is accomplished via the GH receptor (GHR) gene, which is the main factor influencing human development and is essential to optimal functioning of the GH/IGF-I axis. Two GHR isoforms have been studied, according to the presence (flGHR) or absence (d3GHR) of exon 3. The d3GHR variant, which has recently been related to longevity, is associated with enhanced signal transduction and higher receptor function. Many of these studies indicated that the growth response to GH treatment may be affected. Individuals carrying the d3GHR isoform have higher receptor activity, improved signal transduction, and alterations in the treatment response and efficacy compared with those carrying the WT isoform. Further, studies performed in patients with acromegaly, Prader-Willi syndrome, Turner syndrome, small for gestational age (SGA), and growth hormone deficiency (GHD) suggested that the d3GHR variant may have an impact on the relationship between GH and IGF-I levels, height, weight, BMI, and other variables. Other research, however, revealed inconsistent results, which might have been caused by confounding factors, including limited sample sizes and different experimental methods. In this review, we lay out the complexity of the GHR isoforms and provide an overview of the major pharmacogenetic research conducted on this ongoing and unresolved subject.