IGHD II: A Novel GH-1 Gene Mutation (GH-L76P) Severely Affects GH Folding, Stability, and Secretion.
BACKGROUND
The autosomal dominant form of GH deficiency (IGHD II) is characterized by markedly reduced GH secretion combined with low concentrations of IGF-1 leading to short stature.


OBJECTIVE
Structure-function analysis of a missense mutation in the GH-1 gene converting codon 76 from leucine (L) to proline (P) yielding a mutant GH-L76P peptide.


METHODS
Heterozygosity for GH-L76P/wt-GH was identified in a nonconsanguineous Spanish family. The index patients, two siblings, a boy and a girl, were referred for assessment of their short stature (-3.2 and -3.8 SD). Their grandmother, father, and aunt were also carrying the same mutation and showed severe short stature; therefore, IGHD II was diagnosed.


RESULTS
AtT-20 cells coexpressing both wt-GH and GH-L76P showed a reduced GH secretion (P < .001) after forskolin stimulation when compared with the cells expressing only wt-GH. In silico mutagenesis and molecular dynamics simulations presented alterations of correct folding and mutant stability compared with wt-GH. Therefore, further structural analysis of the GH-L76P mutant was performed using expressed and purified proteins in Escherichia coli by thermofluor assay and fast degradation proteolysis assay. Both assays revealed that the GH-L76P mutant is unstable and misfolded compared to wt-GH confirming the bioinformatic model prediction.


CONCLUSIONS
This is the first report of a family suffering from short stature caused by IGHD II, which severely affects intracellular GH folding and stability as well as secretion, highlighting the necessity of functional analysis of any GH variant for defining new mechanisms as a cause for IGHD II.
University Children's Hospital, Department of Pediatric Endocrinology, Diabetology and Metabolism, Inselspital, and Department of Clinical Research, University of Bern, 3010 Bern, Switzerland.
Maria Consolata
MC
Miletta
University Children's Hospital, Department of Pediatric Endocrinology, Diabetology and Metabolism, Inselspital, and Department of Clinical Research, University of Bern, 3010 Bern, Switzerland.
Andrée
A
Eblé
University Children's Hospital, Department of Pediatric Endocrinology, Diabetology and Metabolism, Inselspital, and Department of Clinical Research, University of Bern, 3010 Bern, Switzerland.
Marco
M
Janner
University Children's Hospital, Department of Pediatric Endocrinology, Diabetology and Metabolism, Inselspital, and Department of Clinical Research, University of Bern, 3010 Bern, Switzerland.
Shaheena
S
Parween
University Children's Hospital, Department of Pediatric Endocrinology, Diabetology and Metabolism, Inselspital, and Department of Clinical Research, University of Bern, 3010 Bern, Switzerland.
Amit V
AV
Pandey
University Children's Hospital, Department of Pediatric Endocrinology, Diabetology and Metabolism, Inselspital, and Department of Clinical Research, University of Bern, 3010 Bern, Switzerland.
Christa E
CE
Flück
University Children's Hospital, Department of Pediatric Endocrinology, Diabetology and Metabolism, Inselspital, and Department of Clinical Research, University of Bern, 3010 Bern, Switzerland.
Primus-E
PE
Mullis
D019943:Amino Acid Substitution / Q000235:genetics; D000818:Animals; D001827:Body Height / Q000235:genetics; D002648:Child; D002675:Child, Preschool; D003062:Codon / Q000235:genetics; D005576:Colforsin / Q000494:pharmacology; D019295:Computational Biology; D005190:Family; D005260:Female; D006579:Heterozygote; D019382:Human Growth Hormone / Q000172:deficiency* / Q000235:genetics / Q000378:metabolism; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D051379:Mice; D020125:Mutation, Missense / Q000235:genetics; D010375:Pedigree; D011247:Pregnancy; D011487:Protein Conformation; D017510:Protein Folding
D003062:Codon; D019382:Human Growth Hormone; D005576:Colforsin