Context: GH receptor (GHR) exon 3-deleted/full-length (d3/fl) polymorphism has been proposed to affect the responsiveness to GH therapy. Conventional multiplex PCR genotyping method for this polymorphism detection requires DNA samples, which may be difficult to obtain due to ethical and procedural issues and may limit further studies into the role of this polymorphism in health and disease.
Objective: The objective of the study was to develop a simple genotyping-alternative method for GHRd3 identification by directly measuring serum levels of total GH binding protein (tGHBP) and exon 3-positive GHBP[(E3(+)GHBP] by immunoassay and thereby assess the GHRd3 status.
Design: The GHRd3 genotype was determined by PCR, and tGHBP and E3(+)GHBP levels were measured in serum of 88 healthy adults.
Main outcome measures: The GHRd3 chemotype by ELISA was compared with the genotype by conventional PCR.
Results: The concordance rate of GHR exon 3 status identification between PCR genotyping and ELISA chemotyping was shown to be 100%. There were negligible detectable serum levels of E3(+)GHBP in d3/d3 subjects. The ratio of serum levels E3(+)GHBP vs. tGHBP in fl/fl and d3/fl subjects was (mean ± SD) 96.6 ± 5.1 and 57.1 ± 8.4%, respectively (P < 0.0001). Interestingly, we observed that d3/d3 subjects had significantly lower serum levels of tGHBP compared with fl/fl and d3/fl genotypes.
Conclusions: This dual ELISA against tGHBP and E3(+)GHBP can be used as an alternative method for determining GHRd3 polymorphism status. The implications of differences in serum levels of tGHBP among different genotypes and responsiveness to GH therapy need to be further investigated.