A Novel GHR Intronic Variant, c.266+83G>T, Activates a Cryptic 5' Splice Site Causing Severe GHR Deficiency and Classical GH Insensitivity Syndrome

摘要

Background/Aims: Mutations in the human growth hormone receptor gene (GHR) are the most common cause of growth hormone insensitivity (GHI) syndrome and insulin-like growth factor (IGF-1) deficiency. The extracellular domain of GHR (encoded by exons 2-7 of the GHR gene) can be proteolytically cleaved to circulate as GH-binding protein (GHBP). Methods: We evaluated the cause of classical GHI-(Laron) phenotypes in 3 siblings. Results: Two brothers (aged 16.5 and 14.9 years) and their half-brother (aged 11.3 years) presented with extreme short stature (height standard deviation score, SDS, of-7.05, -6.34 and -8.02, respectively). The parents were consanguineous and of normal stature. Serum GHBP levels of probands were undetectable and circulating IGF-1 and IGF-binding protein-3 were abnormally low, but GH concentrations were elevated. Molecular analysis of the GHR gene revealed homozygous deletion of exon 3, a common polymorphism, and a novel c.266+83G>T variant within intron 4 which generated a 5' donor splice site. Splicing events from this cryptic 5' donor site resulted in retention of 81 intronic nucleotides in the GHR mRNA. Long-term rhlGF-1 therapy combined with leuprolide depot increased height by +2 to +3 SDS. Conclusion: The C.266+ 83G>T is the second intronic GHR mutation identified that activates a cryptic 5' donor splice site. The abnormal splicing event led to early protein termination and undetectable serum GHBP concentrations.