Phenotype and genetic analysis of a syndrome caused by an inactivating mutation in the growth hormone-releasing hormone receptor: Dwarfism of Sindh

Mutational analysis of consanguineous families and their targeted therapy against dwarfism

Dwarfism is a medical term used to describe individuals with a height-vertex measurement that falls below two standard deviations (-2SD) or the third percentile for their gender and age. Normal development of growth is a complicated dynamic procedure that depends upon the coordination of different aspects involving diet, genetics, and biological aspects like hormones in equilibrium. Any severe or acute pathologic procedure may disturb the individual's normal rate of growth. In this research, we examined four (A-D) Pakistani consanguineous families that exhibited syndromic dwarfism, which was inherited in an autosomal recessive pattern. The genomic DNA of each family member was extracted by using phenol-chloroform and Kit methods. Whole Exome Sequencing (WES) of affected family members (IV-11, III-5, IV-4 and III-13) from each group was performed at the Department of Medical Genetics, University of Antwerp, Belgium. After filtering the exome data, the mutations in PPM1F, FGFR3, ERCC2, and PCNT genes were determined by Sanger sequencing of each gene by using specific primers. Afterward, FGFR3 was found to be a suitable drug target among all the mutations to treat achondroplasia also known as disproportionate dwarfism. BioSolveIT softwares were used to discover the lead active inhibitory molecule against FGFR3. This research will not only provide short knowledge to the concerned pediatricians, researchers, and family physicians for the preliminary assessment and management of the disorder but also provide a lead inhibitor for the treatment of disproportionate dwarfism.

Human height: a model common complex trait

CONTEXT

Like other complex phenotypes, human height reflects a combination of environmental and genetic factors, but is notable for being exceptionally easy to measure. Height has therefore been commonly used to make observations later generalised to other phenotypes though the appropriateness of such generalisations is not always considered.

OBJECTIVES

We aimed to assess height's suitability as a model for other complex phenotypes and review recent advances in height genetics with regard to their implications for complex phenotypes more broadly.

METHODS

We conducted a comprehensive literature search in PubMed and Google Scholar for articles relevant to the genetics of height and its comparatibility to other phenotypes.

RESULTS

Height is broadly similar to other phenotypes apart from its high heritability and ease of measurment. Recent genome-wide association studies (GWAS) have identified over 12,000 independent signals associated with height and saturated height's common single nucleotide polymorphism based heritability of height within a subset of the genome in individuals similar to European reference populations.

CONCLUSIONS

Given the similarity of height to other complex traits, the saturation of GWAS's ability to discover additional height-associated variants signals potential limitations to the omnigenic model of complex-phenotype inheritance, indicating the likely future power of polygenic scores and risk scores, and highlights the increasing need for large-scale variant-to-gene mapping efforts.

Can Blood-Circulating Factors Unveil and Delay Your Biological Aging?

According to the World Health Organization, the population of over 60 will double in the next 30 years in the developed countries, which will enforce a further raise of the retirement age and increase the burden on the healthcare system. Therefore, there is an acute issue of maintaining health and prolonging active working longevity, as well as implementation of early monitoring and prevention of premature aging and age-related disorders to avoid early disability. Traditional indicators of biological age are not always informative and often require extensive and expensive analysis. The study of blood factors is a simple and easily accessible way to assess individual health and supplement the traditional indicators of a person's biological age with new objective criteria. With age, the processes of growth and development, tissue regeneration and repair decline; they are gradually replaced by enhanced catabolism, inflammatory cell activity, and insulin resistance. The number of senescent cells supporting the inflammatory loop rises; cellular clearance by autophagy and mitophagy slows down, resulting in mitochondrial and cellular damage and dysfunction. Monitoring of circulated blood factors not only reflects these processes, but also allows suggesting medical intervention to prevent or decelerate the development of age-related diseases. We review the age-related blood factors discussed in recent publications, as well as approaches to slowing aging for healthy and active longevity.

Craniofacial morphology and dental maturity in children with reduced somatic growth of different aetiology and the effect of growth hormone treatment

Children with reduced somatic growth may present various endocrinal diseases, especially growth hormone deficiency (GHD), idiopathic short stature (ISS), chromosomal aberrations, or genetic disorders. In an attempt to normalize the short stature, growth hormone (GH) is administered to these children. The aim of this literature review was to collect information about the craniofacial morphology and dental maturity in these children and to present the existing knowledge on the effect of GH treatment on the above structures.

This review demonstrated that regardless of the origin of the somatic growth retardation, these children show similar craniofacial features, such as short length of the cranial base and the mandible, increased lower facial height, retropositioned mandible, and obtuse gonion angle. On the other hand, dental maturation does not demonstrate a specific pattern. Except for the above findings, muscle alterations seem to be present in individuals with short stature, who present low body muscle mass and strength, while studies on their craniofacial muscles seem to be lacking. After GH administration, the exact amount and pattern of craniofacial growth is unpredictable; however, the facial convexity decreases, mandibular length increases, and posterior facial height increases, while tooth eruption remains unaffected. Thus, it is of great importance to gain more insight into the craniofacial growth of treated and untreated children with reduced somatic growth so that the influence of GH therapy on the various craniofacial structures could be ascertained and proper orthodontic treatment could be selected.

Older individuals heterozygous for a growth hormone-releasing hormone receptor gene mutation are shorter than normal subjects

Growth hormone (GH)-releasing hormone (GHRH) is the most important stimulus for GH secretion by the pituitary gland. Subjects homozygous for GHRH receptor (GHRHR) gene (GHRHR) inactivating mutations have severe GH deficiency, resulting in severe short stature if not treated. We previously reported that young adults heterozygous for the c.57+1G>A null GHRHR mutation (MUT/N) have reduced weight and body mass index (BMI) but normal stature. Here we have studied whether older MUT/N have an additional phenotype. In a cross-sectional study, we measured height, weight and blood pressure, and calculated BMI in two groups (young, 20-40 years of age) and old (60-80 years) of individuals heterozygous for the same GHRHR mutation, and compared with a large number of individuals of normal genotype residing in the same geographical area. Standard deviation score (SDS) of weight was lower, and BMI had a trend toward reduction in young heterozygous compared with young normals, without significant difference in stature. Conversely, SDS of height was lower in older heterozygous individuals than in controls, corresponding to a reduction of 4.2 cm. These data show a reduced stature in older subjects heterozygous for the c.57+1G>A GHRHR mutation, indicating different effects of heterozygosis through lifespan.

Novel growth hormone-releasing hormone receptor gene mutations in Turkish children with isolated growth hormone deficiency

OBJECTIVE

Isolated growth hormone deficiency (IGHD) is defined as a medical condition associated with growth failure due to insufficient production of GH or lack of GH action. Mutations in the gene encoding for GH-releasing hormone receptor (GHRHR) have been detected in patients with IGHD type IB. However, genetic defects on GHRHR causing IGHD in the Turkish population have not yet been reported. To identify mutations on GHRHR gene in a population of Turkish children with IGHD.

METHODS

Ninety-six Turkish children with IGHD were included in this study. Exon1-13 and exon/intron boundaries of GHRHR were amplified by suitable primers. The polymerase chain reaction products for GHRHR gene were sequenced with primers.

RESULTS

We analyzed the GHRHR gene for mutations in ninety-six patients with IGHD based on sequence results. We identified novel p.K264E, p.S317T, p.S330L, p.G369V, p.T257A and C base insertion on position 380 (c.380inserC) mutations. In 5 of the patients, the mutation was homozygote and in 1-heterozygote (p.S317T).

CONCLUSION

Six new missense mutations and one first case of insertion mutations for the GHRHR gene are reported.

Short-term estradiol supplementation potentiates low-dose ghrelin action in the presence of GHRH or somatostatin in older women

CONTEXT

Ghrelin is a potent gastric-derived GH-releasing peptide. How ghrelin interacts with sex steroids, GHRH, and somatostatin (SS) is not known.

OBJECTIVE

Our objective was to test the hypotheses that ghrelin's interactions with GHRH (synergistic) and SS (disinhibitory) are ghrelin dose-dependent and amplified by estrogen. SUBJECTS, SETTING, AND DESIGN: Healthy postmenopausal women were treated with placebo (n=12) or 17β-estradiol (E2) (n=12) at the Center for Translational Science Activities in a randomized double-blind prospective study.

METHODS

Ghrelin dose-dependence was assessed by nonlinear curve fitting of the relationship between deconvolved GH secretory-burst mass and 5 randomly ordered ghrelin doses (0, 0.03, 0.135, 0.6, and 2.7 μg/kg bolus iv) during saline, GHRH, and SS infusion.

RESULTS

Under placebo, neither GHRH nor SS altered the ED50 of ghrelin (range 0.64-0.67 μg/kg). Under E2 (median E2 88 pg/mL), the ED50 of ghrelin declined in the presence of GHRH to 0.52 μg/kg. In contrast, the efficacy of ghrelin rose markedly during GHRH vs saline exposure with and without E2: placebo and saline 52±1.0 vs GHRH 173±3.8 μg/L; and E2 and saline 56±0.90 vs GHRH 174±3.7 μg/L. Sensitivity to ghrelin was similar under all conditions.

SUMMARY

Short-term E2 supplementation in postmenopausal women reduces the ED50 (increases the potency) of ghrelin when GHRH is present, without altering ghrelin efficacy (maximal effect) or hypothalamo-pituitary sensitivity (slope of dose response) to ghrelin. The data suggest possible physiological interactions among sex steroids (endogenous), ghrelin, and GHRH during E2 replacement in postmenopausal women.

Comprehensive RNA-Seq expression analysis of sensory ganglia with a focus on ion channels and GPCRs in Trigeminal ganglia

The specific functions of sensory systems depend on the tissue-specific expression of genes that code for molecular sensor proteins that are necessary for stimulus detection and membrane signaling. Using the Next Generation Sequencing technique (RNA-Seq), we analyzed the complete transcriptome of the trigeminal ganglia (TG) and dorsal root ganglia (DRG) of adult mice. Focusing on genes with an expression level higher than 1 FPKM (fragments per kilobase of transcript per million mapped reads), we detected the expression of 12984 genes in the TG and 13195 in the DRG. To analyze the specific gene expression patterns of the peripheral neuronal tissues, we compared their gene expression profiles with that of the liver, brain, olfactory epithelium, and skeletal muscle. The transcriptome data of the TG and DRG were scanned for virtually all known G-protein-coupled receptors (GPCRs) as well as for ion channels. The expression profile was ranked with regard to the level and specificity for the TG. In total, we detected 106 non-olfactory GPCRs and 33 ion channels that had not been previously described as expressed in the TG. To validate the RNA-Seq data, in situ hybridization experiments were performed for several of the newly detected transcripts. To identify differences in expression profiles between the sensory ganglia, the RNA-Seq data of the TG and DRG were compared. Among the differentially expressed genes (> 1 FPKM), 65 and 117 were expressed at least 10-fold higher in the TG and DRG, respectively. Our transcriptome analysis allows a comprehensive overview of all ion channels and G protein-coupled receptors that are expressed in trigeminal ganglia and provides additional approaches for the investigation of trigeminal sensing as well as for the physiological and pathophysiological mechanisms of pain.

The GH/IGF-1 axis in ageing and longevity

Secretion of growth hormone (GH), and consequently that of insulin-like growth factor 1 (IGF-1), declines over time until only low levels can be detected in individuals aged ≥60 years. This phenomenon, which is known as the 'somatopause', has led to recombinant human GH being widely promoted and abused as an antiageing drug, despite lack of evidence of efficacy. By contrast, several mutations that decrease the tone of the GH/IGF-1 axis are associated with extended longevity in mice. In humans, corresponding or similar mutations have been identified, but whether these mutations alter longevity has yet to be established. The powerful effect of reduced GH activity on lifespan extension in mice has generated the hypothesis that pharmaceutically inhibiting, rather than increasing, GH action might delay ageing. Moreover, mice as well as humans with reduced activity of the GH/IGF-1 axis are protected from cancer and diabetes mellitus, two major ageing-related morbidities. Here, we review data on mouse strains with alterations in the GH/IGF-1 axis and their effects on lifespan. The outcome of corresponding or similar mutations in humans is described, as well as the potential mechanisms underlying increased longevity and the therapeutic benefits and risks of medical disruption of the GH/IGF-1 axis in humans.

Young little mice express a premature cardiovascular aging phenotype

To investigate the effect of growth hormone and insulin-like growth factor 1 deficiency on the aging mouse arterial system, we compared the hemodynamics in young (4 months) and old (30 months) growth hormone-releasing hormone receptor null dwarf (Little) mice and their wild-type littermates. Young Little mice had significantly lower peak and mean aortic velocity and significantly higher aortic impedance than young wild-type mice. However, unlike the wild-type mice, there were no significant changes in arterial function with age in the Little mice. Aortic pulse wave velocity estimated using characteristic impedance increased with age in the wild-type mice, but it changed minimally in the Little mouse. We therefore conclude that arterial function in Little mice expresses a premature aging phenotype at young age and may neither enhance nor reduce their longevity.

Phenotype-genotype correlations in congenital isolated growth hormone deficiency (IGHD)

Isolated growth hormone deficiency (IGHD) may be congenital, often due to genetic mutations, or acquired as a result of other factors such as cranial irradiation. The commonest genes implicated in its genetic etiology are those encoding growth hormone (GH1) and the receptor for GH-releasing hormone (GHRHR). Rarely, IGHD may be caused by mutations in transcription factors (HESX1, SOX3, OTX2) or be the first presentation before the development of other pituitary hormone deficiencies. IGHD has been classified in four genetic forms (type IA, IB, II and III). Despite the increasing number of genes implicated in the etiology of IGHD, mutations in known genes account only for a small percentage of cases; therefore, other as yet unidentified factors may be implicated in its etiology. Although there is no strict genotype/phenotype correlation in patients with IGHD, there are some emerging patterns that may guide us towards a genetic diagnosis of the condition. There is increasing understanding that the phenotype of patients with IGHD is highly variable and sometimes even evolving, dictating the need for long term follow-up in these cases.

Two siblings with isolated GH deficiency due to loss-of-function mutation in the GHRHR gene: successful treatment with growth hormone despite late admission and severe growth retardation

Patients with growth hormone releasing hormone receptor (GHRHR) mutations exhibit pronounced dwarfism and are phenotypically and biochemically indistinguishable from other forms of isolated growth hormone deficiency (IGHD). We presented here two siblings with clinical findings of IGHD due to a nonsense mutation in the GHRHR gene who reached their target height in spite of late GH treatment. Two female siblings were admitted to our clinic with severe short stature at the age of 13.8 (patient 1) and 14.8 years (patient 2). On admission, height in patient 1 was 107 cm (-8.6 SD) and 117 cm (-6.7 SD) in patient 2. Bone age was delayed in both patients (6 years and 9 years). Clinical and biochemical analyses revealed a diagnosis of complete IGHD (peak GH levels on stimulation test was 0.06 ng/mL in patient 1 and 0.16 ng/mL in patient 2). Patients were given recombinant human GH treatment. Genetic analysis of the GH and GHRHR genes revealed that both patientscarried the GHRHR gene mutation p.Glu72X (c.214 G>T) in exon 3 in homozygous (or hemizygous) state. After seven years of GH treatment, the patients reached a final height appropriate for their target height. Final height was 151 cm (-1.5 SD) in patient 1 and 153 cm (-1.2 SD) in patient 2. In conclusion, genetic analysis is indicated in IGHD patients with severe growth failure and a positive family history. In spite of the very late diagnosis in these two patients who presented with severe growth deficit due to homozygous loss-of-function mutations in GHRHR, their final heights reached the target height.

Genetics of isolated growth hormone deficiency

When a child is not following the normal, predicted growth curve, an evaluation for underlying illnesses and central nervous system abnormalities is required, and appropriate consideration should be given to genetic defects causing growth hormone (GH) deficiency (GHD). Because Insulin-like Growth Factor-I (IGF-I) plays a pivotal role, GHD could also be considered as a form of IGF-I deficiency (IGFD). Although IGFD can develop at any level of the GH-releasing hormone (GHRH)-GH-IGF axis, a differentiation should be made between GHD (absent to low GH in circulation) and IGFD (normal to high GH in circulation). The main focus of this review is on the GH gene, the various gene alterations and their possible impact on the pituitary gland. However, although transcription factors regulating the pituitary gland development may cause multiple pituitary hormone deficiency, they may present initially as GHD.

A novel spontaneous mutation of Irs1 in mice results in hyperinsulinemia, reduced growth, low bone mass and impaired adipogenesis

A spontaneous mouse mutant, designated 'small' (sml), was recognized by reduced body size suggesting a defect in the IGF1/GH axis. The mutation was mapped to the chromosome 1 region containing Irs1, a viable candidate gene whose sequence revealed a single nucleotide deletion resulting in a premature stop codon. Despite normal mRNA levels in mutant and control littermate livers, western blot analysis revealed no detectable protein in mutant liver lysates. When compared with the control littermates, Irs1(sml)/Irs1(sml) (Irs1(sml/sml)) mice were small, lean, hearing impaired; had 20% less serum IGF1; were hyperinsulinemic; and were mildly insulin resistant. Irs1(sml/sml) mice had low bone mineral density, reduced trabecular and cortical thicknesses, and low bone formation rates, while osteoblast and osteoclast numbers were increased in the females but not different in the males compared with the Irs1(+/+) controls. In vitro, Irs1(sml/sml) bone marrow stromal cell cultures showed decreased alkaline phosphatase-positive colony forming units (pre-osteoblasts; CFU-AP+) and normal numbers of tartrate-resistant acid phosphatase-positive osteoclasts. Irs1(sml/sml) stromal cells treated with IGF1 exhibited a 50% decrease in AKT phosphorylation, indicative of defective downstream signaling. Similarities between engineered knockouts and the spontaneous mutation of Irs1(sml) were identified as well as significant differences with respect to heterozygosity and gender. In sum, we have identified a spontaneous mutation in the Irs1 gene associated with a major skeletal phenotype. Changes in the heterozygous Irs1(+)(/sml) mice raise the possibility that similar mutations in humans are associated with short stature or osteoporosis.

The molecular basis of hypopituitarism

Hypopituitarism is defined as the deficiency of one or more of the hormones secreted by the pituitary gland. Several developmental factors necessary for pituitary embryogenesis and hormone secretion have been described, and mutations of these genes in humans provide a molecular understanding of hypopituitarism. Genetic studies of affected patients and their families provide insights into possible mechanisms of abnormal pituitary development; however, mutations are rare. This review characterizes several of these developmental proteins and their role in the pathogenesis of hypopituitarism. Continuing research is required to better understand the complexities and interplay between these pituitary factors and to make improvements in genetic diagnosis that can lead to early detection and provide a future cure.

The role of liver-derived insulin-like growth factor-I

IGF-I is expressed in virtually every tissue of the body, but with much higher expression in the liver than in any other tissue. Studies using mice with liver-specific IGF-I knockout have demonstrated that liver-derived IGF-I, constituting a major part of circulating IGF-I, is an important endocrine factor involved in a variety of physiological and pathological processes. Detailed studies comparing the impact of liver-derived IGF-I and local bone-derived IGF-I demonstrate that both sources of IGF-I can stimulate longitudinal bone growth. We propose here that liver-derived circulating IGF-I and local bone-derived IGF-I to some extent have overlapping growth-promoting effects and might have the capacity to replace each other (= redundancy) in the maintenance of normal longitudinal bone growth. Importantly, and in contrast to the regulation of longitudinal bone growth, locally derived IGF-I cannot replace (= lack of redundancy) liver-derived IGF-I for the regulation of a large number of other parameters including GH secretion, cortical bone mass, kidney size, prostate size, peripheral vascular resistance, spatial memory, sodium retention, insulin sensitivity, liver size, sexually dimorphic liver functions, and progression of some tumors. It is clear that a major role of liver-derived IGF-I is to regulate GH secretion and that some, but not all, of the phenotypes in the liver-specific IGF-I knockout mice are indirect, mediated via the elevated GH levels. All of the described multiple endocrine effects of liver-derived IGF-I should be considered in the development of possible novel treatment strategies aimed at increasing or reducing endocrine IGF-I activity.

Unusual phenotypic features in a patient with a novel splice mutation in the GHRHR gene

Isolated growth hormone deficiency (IGHD) may be of genetic origin. One of the few genes involved in that condition encodes the growth hormone releasing hormone receptor (GHRHR) that, through its ligand (GHRH), plays a pivotal role in the GH synthesis and secretion by the pituitary. Our objective is to describe the phenotype of two siblings born to a consanguineous union presenting with short stature (IGHD) and Magnetic Resonance Imaging (MRI) abnormalities, and to identify the molecular basis of this condition. Our main outcome measures were clinical and endocrinological investigations, MRI of the pituitary region, study of the GHRHR gene sequence and transcripts. In both patients, the severe growth retardation (-5SD) was combined with anterior pituitary hypoplasia. In addition to these classical phenotypic features for IGHD, one of the patients had a Chiari I malformation, an arachnoid cyst, and a dysmorphic anterior pituitary. A homozygous sequence variation in the consensus donor splice site of intron 1 (IVS1 + 2T > G) of the GHRHR gene was identified in both patients. Using in vitro transcription assay, we showed that this mutation results in abnormal splicing of GHRHR transcripts. In this report, which broadens the phenotype associated with GHRHR defects, we discuss the possible role of the GHRHR in the proper development of extrapituitary structures, through a mechanism that could be direct or secondary to severe GH deficiency.

Isolated growth hormone deficiency

Isolated growth hormone deficiency (IGHD) represents conditions of GH deficiency that are not necessarily associated with other pituitary hormone deficiencies or with an organic lesion. Three sub-categories of IGHD have been clinically identified (IGHD types 1-3), and IGHD type 1 has been further separated into IGHD types 1a and b. However, this clinical sub-categorization of IGHD may need reconsideration due to the recent identification of molecular heterogeneity within each sub-type of IGHD. In a small number of children with IGHD, defects in the GH, GH-releasing hormone receptor (GHRH-R), and GH1 genes have been identified. In most cases, no cause for IGHD can be identified; however, the proportion of idiopathic IGHD cases may be decreasing due to identification of causative factors. The phenotype of IGHD is variable depending in part on the underlying genetic disorders in the affected individuals. Several studies have focused on the usefulness of MRI findings in patients with GHD but anatomic abnormalities of the pituitary gland are variable. We review current studies and the clinical, biochemical, and molecular features described for different groups of affected individuals with IGHD.

GH response to hypoglycemia and clonidine in the GH-releasing hormone resistance syndrome

GH secretion by the pituitary is the result of the balance between the stimulatory effect of GHRH and the inhibitory effect of SS. Patients with mutations in GHRH receptor (GHRH-R) gene (GHRH-R) offer a unique model to study the mechanism of action of different GH secretion stimuli. In the past, we have demonstrated a small but significant GH response to a GH secretagogue (GHRP-2) in a homogenous cohort of patients with severe GH deficiency (GHD) due to a homozygous null mutation in GHRH-R (IVS1+1G-->A). Now, we sought to determine if we could detect a GH response to hypoglycemia (ITT: insulin tolerance test) or clonidine (CL) in these patients. Nine young GHD subjects underwent both ITT and CL tests, and 2 additional subjects underwent only CL test. There was a small but significant GH increase during ITT, but not during CL test. These results indicate that a minimal albeit significant GH response to ITT can occur despite complete lack of GHRH-R function.

A germ line mutation that delays prostate cancer progression and prolongs survival in a murine prostate cancer model

Circulating insulin-like growth factor-I (IGF-I) levels have been shown to be related to risk of prostate cancer in epidemiologic studies. While specific genetic loci responsible for interindividual variation in circulating IGF-I levels in normal men have not been identified, candidate genes include those involved in the growth hormone (GH)-IGF-I axis such as the hypothalamic factors GH releasing hormone (GHRH) and somatostatin and their receptors. To investigate the role of the GH-IGF-I axis on in vivo prostate carcinogenesis and neoplastic progression, we generated mice genetically predisposed to prostate cancer (the TRAMP model) to be homozygous for lit, a mutation that inactivates the GHRH receptor (GHRH-R) and reduces circulating levels of GH and IGF-I. The lit mutation significantly reduced the percentage of the prostate gland showing neoplastic changes at 35 weeks of age (P=0.0005) and was also associated with improved survival (P<0.01). These data provide an example of a germ line mutation that reduces risk in an experimental prostate carcinogenesis model. The results suggest that prostate carcinogenesis and progression may be influenced by germ line variation of genes encoding signalling molecules in the GH-IGF-I axis.