Growth Hormone Receptor (GHR) 6Ω Pseudoexon Activation: a Novel Cause of Severe Growth Hormone Insensitivity.

CONTEXT

Severe forms of growth hormone insensitivity (GHI) are characterized by extreme short stature, dysmorphism, and metabolic anomalies.

OBJECTIVE

This work aims to identify the genetic cause of growth failure in 3 "classical" GHI individuals.

METHODS

A novel intronic growth hormone receptor gene (GHR) variant was identified, and in vitro splicing assays confirmed aberrant splicing. A 6Ω pseudoexon GHR vector and patient fibroblast analysis assessed the consequences of the novel pseudoexon inclusion and the impact on GHR function.

RESULTS

We identified a novel homozygous intronic GHR variant (g.5:42700940T > G, c.618+836T > G), 44 bp downstream of the previously recognized intronic 6Ψ GHR pseudoexon mutation in the index patient. Two siblings also harbored the novel intronic 6Ω pseudoexon GHR variant in compound heterozygosity with the known GHR c.181C > T (R43X) mutation. In vitro splicing analysis confirmed inclusion of a 151-bp mutant 6Ω pseudoexon not identified in wild-type constructs. Inclusion of the 6Ω pseudoexon causes a frameshift resulting in a nonfunctional truncated GHR lacking the transmembrane and intracellular domains. The truncated 6Ω pseudoexon protein demonstrated extracellular accumulation and diminished activation of STAT5B signaling following GH stimulation.

CONCLUSION

Novel GHR 6Ω pseudoexon inclusion results in loss of GHR function consistent with a severe GHI phenotype. This represents a novel mechanism of Laron syndrome and is the first deep intronic variant identified causing severe postnatal growth failure. The 2 kindreds originate from the same town in Campania, Southern Italy, implying common ancestry. Our findings highlight the importance of studying variation in deep intronic regions as a cause of monogenic disorders.