The GHR gene on chromosome 5 encodes the growth hormone receptor. Mutations in the GHR gene can lead to altered sensitivity to growth hormone, resulting in abnormal height (among other characteristics).
There are 2 major forms of the GHR mRNA in humans, based on whether exon 3 is present or absent. The full-length form is the most prevalent form, but the isoform lacking exon 3, which is known as d3GHR or d3-GHR, is found in most populations worldwide at a low but still significant frequency (~10% of individuals in many populations are d3/d3 homozygotes). The d3-GHR form is generated from a GHR (germline) allele that lacks exon 3; it is not generated by alternative splicing.
An interesting although preliminary study published in 2017 concluded that males carrying two d3-GHR alleles lived ~10 years longer than those carrying one or more full-length alleles; on average, these males were also 1 inch taller, had lower serum IGF-1 levels, and were more responsive to growth hormone. Male centenarians were also more likely to have two d3-GHR alleles than non-centenarians. Note that these longevity effects were not seen in females.10.1126/sciadv.1602025
There are at least two SNPs that 'tag' the d3-GHR allele with near certainty, at least in Caucasian/European populations (and perhaps others) and that are also present on most genotyping chips. [PMID 23740230],[PMID 17220348] These SNPs, shown below with the tagging (minor) allele correlated with the d3-GHR allele, are: