Severe growth failure associated with a novel heterozygous nonsense mutation in the GHR transmembrane domain leading to elevated growth hormone binding protein

Skeletal overgrowth in a pre-pubescent child treated with pan-FGFR inhibitor

Fibroblast growth factors and their receptors (FGFR) have major roles in both human growth and oncogenesis. In adults, therapeutic FGFR inhibitors have been successful against tumors that carry somatic FGFR mutations. In pediatric patients, trials testing these anti-tumor FGFR inhibitor therapeutics are underway, with several recent reports suggesting modest positive responses. Herein, we report an unforeseen outcome in a pre-pubescent child with an FGFR1-mutated glioma who was successfully treated with FDA-approved erdafitinib, a pan-FGFR inhibitor approved for treatment of Bladder tumors. While on treatment with erdafitinib, the patient experienced rapid skeletal and long bone overgrowth resulting in kyphoscoliosis, reminiscent of patients with congenital loss-of-function FGFR3 mutations. We utilized normal dermal fibroblast cells established from the patient as a surrogate model to demonstrate that insulin-like growth factor 1 (IGF-1), a factor important for developmental growth of bones and tissues, can activate the PI3K/AKT pathway in erdafitinib-treated cells but not the MAPK/ERK pathway. The IGF-I-activated PI3K/AKT signaling rescued normal fibroblasts from the cytotoxic effects of erdafitinib by promoting cell survival. We, therefore, postulate that IGF-I-activated P13K/AKT signaling likely continues to promote bone elongation in the growing child, but not in adults, treated with therapeutic pan-FGFR inhibitors. Importantly, since activated MAPK signaling counters bone elongation, we further postulate that prolonged blockage of the MAPK pathway with pan-FGFR inhibitors, together with actions of growth-promoting factors including IGF-1, could explain the abnormal skeletal and axial growth suffered by our pre-pubertal patient during systemic therapeutic use of pan-FGFR inhibitors. Further studies to find more targeted, and/or appropriate dosing, of pan-FGFR inhibitor therapeutics for children are essential to avoid unexpected off-target effects as was observed in our young patient.

A Clinical Trial of High Dose Growth Hormone in a Patient with a Dominant Negative Growth Hormone Receptor Mutation

CONTEXT

Rare patients with short stature and growth hormone (GH) resistance have dominant-negative variants in the GH receptor. We describe a patient with GH resistance due to elevated levels of GH binding protein and demonstrate the potential for a precision medicine intervention.

OBJECTIVE

To determine whether high dose GH can overcome GH resistance in this specific patient resulting in normal IGF-1 levels and improved growth rates.

DESIGN

Single patient trial of ascending doses of GH followed by dose stable phase; total 12 months of treatment.

PATIENT

Patient has a heterozygous variant in GH receptor resulting in elevated levels of GH binding protein manifesting as GH resistance and severe short stature.

INTERVENTIONS

Daily subcutaneous GH starting at 50 micrograms/kg/day and escalating to 250 micrograms/kg/day until goal IGF-1 achieved. Subject continued 250 micrograms/kg/day for a total treatment duration of 12 months.

OUTCOME MEASURES

The primary outcome measure was the dose of GH required to achieve an IGF-1 level above the mid-point of the normal range. Secondary endpoints included height velocity and the change in height SDS during the 1st year of treatment.

RESULTS

A dose of GH of 250 micrograms/kg/day achieved the target IGF-1 level. The patient's annualized height velocity was 8.7 cm/year, an increase of 3.4 cm/year from baseline, resulting in a 0.81 SD gain in height.

CONCLUSIONS

A precision medicine approach of extremely high dose GH was able to overcome GH resistance in a patient with a dominant-negative variant in the GH receptor resulting in elevated GH binding protein levels.

Reporting a novel growth hormone receptor gene variant in an Iranian consanguineous pedigree with Laron syndrome: a case report

BACKGROUND

Human growth hormone (hGH) plays a crucial role in growth by binding to growth hormone receptor (GHR) in target cells. Binding of GH molecules to their cognate receptors triggers downstream signaling pathways leading to the transcription of several genes, including insulin-like growth factor (IGF)-1. Pathogenic variants in the GHR gene can result in structural and functional defects in the GHR protein, leading to Laron Syndrome (LS) with the primary clinical manifestation of short stature. So far, around 100 GHR variants have been reported, mostly biallelic, as causing LS.

CASE PRESENTATION

We report on three siblings from an Iranian consanguineous family who presented with dwarfism. Whole-exome sequencing (WES) was performed on the proband, revealing a novel homozygous missense variant in the GHR gene (NM_000163.5; c.610 T > A, p.(Trp204Arg)) classified as a likely pathogenic variant according to the recommendation of the American College of Medical Genetics (ACMG). Co-segregation analysis was investigated using Sanger sequencing.

CONCLUSIONS

To date, approximately 400-500 LS cases with GHR biallelic variants, out of them 10 patients originating from Iran, have been described in the literature. Given the high rate of consanguineous marriages in the Iranian population, the frequency of LS is expected to be higher, which might be explained by undiagnosed cases. Early diagnosis of LS is very important, as treatment is available for this condition.

Characterization of dominant-negative growth hormone receptor variants reveals a potential therapeutic target for short stature

OBJECTIVE

Growth hormone insensitivity (GHI) encompasses growth restriction, normal/elevated growth hormone (GH), and low insulin-like growth factor I (IGF1). "Nonclassical" GHI is poorly characterized and is rarely caused by heterozygous dominant-negative (DN) variants located in the intracellular or transmembrane domains of the GH receptor (GHR). We sought to determine the molecular mechanisms underpinning the growth restriction in 2 GHI cases.

METHODS AND DESIGN

A custom-made genetic investigative pipeline was exploited to identify the genetic cause of growth restriction in patients with GHI. Nanoluc binary technology (NanoBiT), in vitro splicing assays, western blotting, and flow cytometry, characterized the novel GHR variants.

RESULTS

Novel heterozygous GHR variants were identified in 2 unrelated patients with GHI. In vitro splicing assays indicated both variants activated the same alternative splice acceptor site resulting in aberrant splicing and exclusion of 26 base pairs of GHR exon 9. The GHR variants produced truncated receptors and impaired GH-induced GHR signaling. NanoBiT complementation and flow cytometry showed increased cell surface expression of variant GHR homo/heterodimers compared to wild-type (WT) homodimers and increased recombinant human GH binding to variant GHR homo/heterodimers and GH binding protein (GHBP) cleaved from the variant GHRs. The findings demonstrated increased variant GHR dimers and GHBP with resultant GH sequestration.

CONCLUSION

We identified and characterized 2 novel, naturally occurring truncated GHR gene variants. Intriguingly, these DN GHR variants act via the same cryptic splice acceptor site, highlighting impairing GH binding to excess GHBP as a potential therapeutic approach.

Effects of zearalenone on ovarian development of prepubertal gilts through growth hormone axis

This experiment aimed to establish the effects of zearalenone (ZEN) on ovarian development in prepubertal gilts through the growth hormone axis [growth hormone-releasing hormone (GHRH) / growth hormone (GH) / growth hormone receptor (GHR)]. In a 40-day experiment, 48 Landrace × Yorkshire crossbred prepubertal gilts were randomly allocated to four dietary treatments, including a basal diet supplemented with 0 (control), 400 (T1), 800 (T2), and 1,600 (T3) μg/kg ZEN. The ovary index of T2 (P = 0.058) and T3 (P = 0.065) increased compared to the control group. Besides, histopathological examination revealed that ZEN promoted the development of ovaries and follicles. The GHR content, relative expression levels of GHR, janus activated kinase 2 (JAK2) mRNA, and mean optical density of GHR in the ovaries of prepubertal gilts in the T2 experimental group increased significantly at P < 0.05 compared to the control group. The T3 group had significantly higher GHR content, relative JAK2 expression levels, and signal transducer and activator of transcriptions 3 (STAT3) mRNA. In conclusion, ZEN enhances the biological effect of GH, promotes the development of the ovary (follicle), and exerts reproductive toxicity by increasing the expression level of GHR, JAK2, and STAT3 mRNA ovary and immune intensity of GHR protein.

Growth Hormone Receptor (Ghr) 6ω Pseudoexon Activation: A Novel Cause Of Severe Growth Hormone Insensitivity (Ghi)

CONTEXT

Severe forms of Growth Hormone Insensitivity (GHI) are characterized by extreme short stature, dysmorphism and metabolic anomalies.

OBJECTIVE

Identification of the genetic cause of growth failure in 3 'classical' GHI subjects.

DESIGN

A novel intronic 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), 44bp 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 151bp mutant 6Ω pseudoexon not identified in wild-type constructs. Inclusion of the 6Ω pseudoexon causes a frameshift resulting in a non-functional truncated GHR lacking the transmembrane and intracellular domains. The truncated 6Ω pseudoexon protein demonstrated extracellular accumulation and diminished activation of STAT5B signaling following growth hormone 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.

Laron syndrome - A historical perspective

Laron Syndrome (LS) [OMIm#262500], or primary GH insensitivity, was first described in 1966 in consanguineous Jewish families from Yemen. LS is characterized by a typical phenotype that includes dwarfism, obesity and hypogenitalism. The disease is caused by deletions or mutations of the GH-receptor gene, causing high serum GH and low IGF-I serum levels. We studied 75 patients from childhood to adult age. After early hypoglycemia due to the progressive obesity, patients tend to develop glucose intolerance and diabetes. The treatment is by recombinant IGF-I, which improves the height and restores some of the metabolic parameters. An unexpected finding was that patients homozygous for GH-R defects are protected from malignancy lifelong, not so heterozygotes or double heterozygote subjects. We estimate that there are at least 500 patients worldwide, unfortunately only few treated.

Identification and In Vitro Functional Verification of Two Novel Mutations of GHR Gene in the Chinese Children with Laron Syndrome

PURPOSE

Laron syndrome (LS) is a severe growth disorder caused by GHR gene mutation or post-receptor pathways defect. The clinical features of these patients collected in our present study were summarized, GHR gene variants were investigated and further in vitro functional verification was carried out.

METHODS

Four patients with LS were collected, their clinical characteristics were summarized, genomic DNA was extracted, and GHR gene was amplified and sequenced. GHR wild type (GHR-WT) and mutant GHR expression plasmids were constructed, and transiently transfected into HepG2 cells and HEK293T cells to observe the subcellular distribution of the GHR protein by immunofluorescence and to determine the expression of GHR and its post-receptor signaling pathway changes by Western blotting.

RESULTS

All of the four patients were male, and the median height was -4.72 SDS. Four GHR gene variants including c.587A>C (p.Y196S), c.766C>T (p.Q256*), c.808A>G (p.I270V) and c.1707-1710del (p.E570Afs*30) were identified, and the latter two were novel mutations. The results of mutant GHR plasmids transfection experiments and immunofluorescence assay showed that the subcellular distribution of GHR-Q256* and GHR-E570Afs*30 mutant proteins in HepG2 and HEK293T cells presented with a unique ring-like pattern, gathering around the nucleus, while GHR-Y196S mutant protein was evenly distributed on HepG2 cell membrane similar to GHR-WT. The GHR protein levels of HepG2 cells transiently transfected with GHR-Y196S, GHR-Q256* and GHR-E570Afs*30 were all significantly lower when compared with cells transfected with GHR-WT (P<0.05). Further mutant GHR post-receptor signal transduction investigation demonstrated that GH induced phosphorylated STAT5 levels of HepG2 cells transfected with three mutant plasmids were all significantly decreased in comparison with that of GHR-WT (P<0.05).

CONCLUSIONS

Two novel GHR gene mutations (I270V and E570Afs*30) were found in our patients with LS. GHR mutations influenced the subcellular distribution and GHR protein levels, then led to the impaired post-receptor signal transduction, suggesting that the GHR mutations contributed to the pathological condition of LS patients.