A mosaic de novo duplication of 17q21-25 is associated with GH insensitivity, disturbed in vitro CD28-mediated signaling, and decreased STAT5B, PI3K, and NF-κB activation

Case Report: A child with NFKB1 haploinsufficiency explaining the linkage between immunodeficiency and short stature

We report the case of a patient with common variable immunodeficiency (CVID) presenting with short stature and treated with recombinant human growth hormone (rhGH). Whole exome sequencing revealed a novel single-nucleotide duplication in the NFKB1 gene (c.904dup, p.Ser302fs), leading to a frameshift and thus causing NFKB1 haploinsufficiency. The variant was considered pathogenic and was later found in the patient's mother, also affected by CVID. This is the first reported case of a patient with CVID due to NFKB1 mutation presenting with short stature. We analyzed the interconnection between NFKB1 and GH - IGF-1 pathways and we hypothesized a common ground for both CVID and short stature in our patient.

Regulatory role of NF-κB in growth plate chondrogenesis and its functional interaction with Growth Hormone

Nuclear Factor kappa B (NF-kB) is a family of transcription factors that participates in the regulation of cell proliferation, migration, and apoptosis. Impaired NF-kB activity appears to be involved in the pathophysiology of inflammatory states, autoimmune diseases, and cancer. Genetic manipulation in mice leading to impaired NF-kB function is associated with abnormal limb development and delayed bone growth. We have previously shown in rodent cultured chondrocytes and cultured metatarsal bones that NF-kB promotes longitudinal bone growth and growth plate chondrocyte function. These NF-kB growth-promoting effects appear to be facilitated by Growth Hormone (GH) and Insulin-like Growth factor-1 (IGF-1). These stimulatory effects of GH and IGF-1 on NF-kB activity are supported by observational evidence in humans; a number of individuals carrying mutations that alter NF-kB function exhibit growth failure and GH insensitivity.

Nonclassical GH Insensitivity: Characterization of Mild Abnormalities of GH Action

GH insensitivity (GHI) presents in childhood with growth failure and in its severe form is associated with extreme short stature and dysmorphic and metabolic abnormalities. In recent years, the clinical, biochemical, and genetic characteristics of GHI and other overlapping short stature syndromes have rapidly expanded. This can be attributed to advancing genetic techniques and a greater awareness of this group of disorders. We review this important spectrum of defects, which present with phenotypes at the milder end of the GHI continuum. We discuss their clinical, biochemical, and genetic characteristics. The objective of this review is to clarify the definition, identification, and investigation of this clinically relevant group of growth defects. We also review the therapeutic challenges of mild GHI.

17p13.1 Microduplication Syndrome in a Child, Familial Short Stature, and Growth Hormone Deficiency: A Case Report and Review of the Literature

To date, 6 cases of 17p13.1 microduplications have been described in the literature. Intellectual disability is the core feature, together with minor facial dysmorphisms and obesity. We describe the first case of a young patient with a maternally inherited microduplication in 17p13.1 presenting with growth hormone deficiency. The boy was addressed to the endocrine division for growth retardation (weight and height <3rd percentile). Besides minor facial dysmorphisms, physical and neurological examinations were normal except for motor dyspraxia. Basic blood tests and endocrinological investigations were normal, but IGF1 levels were low for his age. Growth hormone deficiency was confirmed. Hypothalamic pituitary MRI was normal. His karyotype was 46XY. Array-CGH analysis detected a 422-kb copy number gain in the spanning region 17p13.1 inherited from his mother. Although familial short stature is considered a "normal" variation of growth retardation, hormonal and genetic investigation is essential in the etiological diagnosis.

Growth hormone signaling pathways

Over 20years ago, our laboratory showed that growth hormone (GH) signals through the GH receptor-associated tyrosine kinase JAK2. We showed that GH binding to its membrane-bound receptor enhances binding of JAK2 to the GHR, activates JAK2, and stimulates tyrosyl phosphorylation of both JAK2 and GHR. The activated JAK2/GHR complex recruits a variety of signaling proteins, thereby initiating multiple signaling pathways and cellular responses. These proteins and pathways include: 1) Stat transcription factors implicated in the expression of multiple genes, including the gene encoding insulin-like growth factor 1; 2) Shc adapter proteins that lead to activation of the grb2-SOS-Ras-Raf-MEK-ERK1,2 pathway; 3) insulin receptor substrate proteins implicated in the phosphatidylinositol-3-kinase and Akt pathway; 4) signal regulatory protein α, a transmembrane scaffold protein that recruits proteins including the tyrosine phosphatase SHP2; and 5) SH2B1, a scaffold protein that can activate JAK2 and enhance GH regulation of the actin cytoskeleton. Our recent work has focused on the function of SH2B1. We have shown that SH2B1β is recruited to and phosphorylated by JAK2 in response to GH. SH2B1 localizes to the plasma membrane, cytoplasm and focal adhesions; it also cycles through the nucleus. SH2B1 regulates the actin cytoskeleton and promotes GH-dependent motility of RAW264.7 macrophages. Mutations in SH2B1 have been found in humans exhibiting severe early-onset childhood obesity and insulin resistance. These mutations impair SH2B1 enhancement of GH-induced macrophage motility. As SH2B1 is expressed ubiquitously and is also recruited to a variety of receptor tyrosine kinases, our results raise the possibility that effects of SH2B1 on the actin cytoskeleton in various cell types, including neurons, may play a role in regulating body weight.

Atypical defects resulting in growth hormone insensitivity

Besides four well-documented genetic causes of GH insensitivity (GHI) (GHR, STAT5B, IGF1, IGFALS defects), several other congenital and acquired conditions are associated with GHI. With respect to its anabolic actions, GH induces transcription of IGF1, IGFBP3 and IGFALS through a complex regulatory cascade including GH binding to its receptor (GHR), activation of JAK2 and phosphorylation of STAT5b, which then trafficks to the nucleus. GH also activates the MAPK and PI3K pathways. The synthesis of GHR can be reduced by estrogen deficiency or corticosteroid excess, and is possibly decreased in African pygmies. An increased degradation of GHRs because of overexpression of cytokine-inducible SH2-containing protein (CIS) was suggested for some children with idiopathic short stature. Effects on several downstream components of GH signaling were observed for FGF21, cytokines, sepsis, fever and chronic renal failure. In Noonan syndrome and other "rasopathies" the activation of the RAS-RAF-MAPK-ERK pathway leads to inhibition of the JAK/STAT pathway. In contrast, fibroblasts from tall patients with Sotos syndrome showed a downregulation of this axis. Experimental and clinical evidence suggests that the NF-κB pathway plays a role in GH signaling. In a patient with an IκBα mutation presenting with short stature, GHI, severe immune deficiency and other features, NF-κB nuclear transportation and STAT5 and PI3K expression and activity were reduced. A patient with a mosaic de novo duplication of 17q21-25 presented with several congenital anomalies, GHI and mild immunodeficiency. Studies in blood lymphocytes showed disturbed signaling of the CD28 pathway, involving NF-κB and related proteins. Functional studies on skin fibroblasts revealed that NF-κB activation, PI3K activity and STAT5 phosphorylation in response to GH were suppressed, while the sensitivity to GH in terms of MAPK phosphorylation was increased. The expression of one of the duplicated genes, PRKCA, was significantly higher than in control cells, which might be the cause of this clinical syndrome.

MECHANISMS IN ENDOCRINOLOGY: Novel genetic causes of short stature

The fast technological development, particularly single nucleotide polymorphism array, array-comparative genomic hybridization, and whole exome sequencing, has led to the discovery of many novel genetic causes of growth failure. In this review we discuss a selection of these, according to a diagnostic classification centred on the epiphyseal growth plate. We successively discuss disorders in hormone signalling, paracrine factors, matrix molecules, intracellular pathways, and fundamental cellular processes, followed by chromosomal aberrations including copy number variants (CNVs) and imprinting disorders associated with short stature. Many novel causes of GH deficiency (GHD) as part of combined pituitary hormone deficiency have been uncovered. The most frequent genetic causes of isolated GHD are GH1 and GHRHR defects, but several novel causes have recently been found, such as GHSR, RNPC3, and IFT172 mutations. Besides well-defined causes of GH insensitivity (GHR, STAT5B, IGFALS, IGF1 defects), disorders of NFκB signalling, STAT3 and IGF2 have recently been discovered. Heterozygous IGF1R defects are a relatively frequent cause of prenatal and postnatal growth retardation. TRHA mutations cause a syndromic form of short stature with elevated T3/T4 ratio. Disorders of signalling of various paracrine factors (FGFs, BMPs, WNTs, PTHrP/IHH, and CNP/NPR2) or genetic defects affecting cartilage extracellular matrix usually cause disproportionate short stature. Heterozygous NPR2 or SHOX defects may be found in ∼3% of short children, and also rasopathies (e.g., Noonan syndrome) can be found in children without clear syndromic appearance. Numerous other syndromes associated with short stature are caused by genetic defects in fundamental cellular processes, chromosomal abnormalities, CNVs, and imprinting disorders.

Insulin-Like Growth Factor-Independent Effects of Growth Hormone on Growth Plate Chondrogenesis and Longitudinal Bone Growth

GH stimulates growth plate chondrogenesis and longitudinal bone growth directly at the growth plate. However, it is not clear yet whether these effects are entirely mediated by the local expression and action of IGF-1 and IGF-2. To determine whether GH has any IGF-independent growth-promoting effects, we generated (TamCart)Igf1r(flox/flox) mice. The systemic injection of tamoxifen in these mice postnatally resulted in the excision of the IGF-1 receptor (Igf1r) gene exclusively in the growth plate. (TamCart)Igf1r(flox/flox) tamoxifen-treated mice [knockout (KO) mice] and their Igf1r(flox/flox) control littermates (C mice) were injected for 4 weeks with GH. At the end of the 4-week period, the tibial growth and growth plate height of GH-treated KO mice were greater than those of untreated C or untreated KO mice. The systemic injection of GH increased the phosphorylation of Janus kinase 2 and signal transducer and activator of transcription 5B in the tibial growth plate of the C and KO mice. In addition, GH increased the mRNA expression of bone morphogenetic protein-2 and the mRNA expression and protein phosphorylation of nuclear factor-κB p65 in both C and KO mice. In cultured chondrocytes transfected with Igf1r small interfering RNA, the addition of GH in the culture medium significantly induced thymidine incorporation and collagen X mRNA expression. In conclusion, our findings demonstrate that GH can promote growth plate chondrogenesis and longitudinal bone growth directly at the growth plate, even when the local effects of IGF-1 and IGF-2 are prevented. Further studies are warranted to elucidate the intracellular molecular mechanisms mediating the IGF-independent, growth-promoting GH effects.

Characterizing short stature by insulin-like growth factor axis status and genetic associations: results from the prospective, cross-sectional, epidemiogenetic EPIGROW study

CONTEXT

Serum IGF-I levels are often low in patients with short stature (SS) without defined etiology. Hence, genetic investigations have focused on the GH-IGF-I axis.

OBJECTIVE

Our objectives were to characterize IGF-I axis status and search for a broader range of genetic associations in children with SS and normal GH.

DESIGN AND SETTING

We conducted a prospective, cross-sectional, epidemiogenetic case-control study in 9 European countries (2008-2010).

PARTICIPANTS

Children (n = 275) aged ≥2 years with SS without defined etiology (≤-2.5 height SD score [SDS]) and ≥1 peak GH ≥7 μg/L) were recruited.

METHODS

Serum IGF-I, IGF-binding protein-3 (IGFBP-3), and acid-labile subunit (ALS) levels were measured in a central laboratory. Candidate gene exome sequencing was performed in this cohort and ethnicity-matched controls.

RESULTS

Serum IGF-I, IGFBP-3, and ALS levels were highly correlated, but there was a discrepancy between prevalence of IGF-I, IGFBP-3, and ALS deficiencies (53%, 30%, and 0.8%, respectively). An insertion-deletion (Indel) on the IGF1 gene (P = 1.2 × 10(-5), Bonferroni-corrected; case vs control frequency: 0.04 vs 0.112), an Indel on NFKB1 (P = 1.36 × 10(-10); case vs control frequency: 0.464 vs 0.272), and 2 single-nucleotide polymorphisms on ZBTB38 (P < 2.3 × 10(-6)) were associated with SS. At P < 10(-4), single-nucleotide polymorphisms on genes related to protein kinase regulation, MAPK, and Fanconi pathways were also associated with SS.

CONCLUSIONS

IGF-I deficiency is a common feature in SS without defined etiology; an Indel in the IGF1 gene was associated with SS. However, genes involved in transcriptional regulation (NFKB1 and ZBTB38) and growth factor signaling were also associated, providing further candidates for genetic investigations on individual patients.