The Distribution of Exon 3-Deleted/Full-Length Growth Hormone Receptor Polymorphism in the Turkish Population

Objective: The exon 3-deleted/full-length (d3/fl) growth hormone receptor (d3/fl-GHR) polymorphism has been associated with responsiveness to GH therapy in some children and also with adult height variation in the general population. We aimed to evaluate the distribution of d3/fl-GHR polymorphism in a Turkish population.
Methods: The study included 477 (54 females/423 males) healthy adults with a mean±SD age of 31.1±9.0 years (range: 18-57). Height and body mass index (BMI) were expressed as standard deviation score (SDS) according to national standards. All adults had normal height and BMI SDSs (between -2 and +2). GHR exon 3 isoforms were studied by simple multiplex polymerase chain reaction method. Insulin-like growth factor-1 (IGF-1) and IGF-binding protein-3 (IGFBP-3) values were also measured and expressed as SDS.
Results: The distribution of the GHR exon 3 genotypes in the Turkish healthy adults was 35% (n=167) for fl/fl, 39% (n=186) for fl/d3, and 26% (n=124) for d3/d3. There was no difference between genders in GHR exon 3 genotypes. Frequencies of fl allele and d3 allele were 54.5% and 45.5%, respectively. There were no differences in height SDS and BMI SDS among the three d3/fl-GHR genotype groups. There was a significant difference in IGFBP-3 SDS between fl/fl and fl/d3 groups (p=0.022).
Conclusions: This study presents the results of GHR polymorphism in a Turkish population as a reference for further studies. The distribution was similiar to European populations. There were no correlations between GHR isoforms and height SDS or other clinical/biochemical characteristics of the individuals except for higher IGFBP-3 levels in the fl/d3 group as compared to the fl/fl group. Whether this finding implies an abnormality, needs further investigation.