Diverse deletions in the growth hormone receptor gene cause growth hormone insensitivity syndrome

Integrative Analyses of miRNA-mRNA Interactions Reveal let-7b, miR-128 and MAPK Pathway Involvement in Muscle Mass Loss in Sex-Linked Dwarf Chickens

The sex-linked dwarf (SLD) chicken is an ideal model system for understanding growth hormone (GH)-action and growth hormone receptor (GHR) function because of its recessive mutation in the GHR gene. Skeletal muscle mass is reduced in the SLD chicken with a smaller muscle fiber diameter. Our previous study has presented the mRNA and miRNA expression profiles of the SLD chicken and normal chicken between embryo day 14 and seven weeks of age. However, the molecular mechanism of GHR-deficient induced muscle mass loss is still unclear, and the key molecules and pathways underlying the GHR-deficient induced muscle mass loss also remain to be illustrated. Here, by functional network analysis of the differentially expressed miRNAs and mRNAs between the SLD and normal chickens, we revealed that let-7b, miR-128 and the MAPK pathway might play key roles in the GHR-deficient induced muscle mass loss, and that the reduced cell division and growth are potential cellular processes during the SLD chicken skeletal muscle development. Additionally, we also found some genes and miRNAs involved in chicken skeletal muscle development, through the MAPK, PI3K-Akt, Wnt and Insulin signaling pathways. This study provides new insights into the molecular mechanism underlying muscle mass loss in the SLD chickens, and some regulatory networks that are crucial for chicken skeletal muscle development.

Clinical and biochemical consequences of an intragenic growth hormone receptor (GHR) deletion in a large Chinese pedigree

OBJECTIVE

Growth hormone insensitivity (GHI) may be caused by failure of GH receptor function. Some patients bearing specific GHR mutations differ from classical GHI individuals by extremely elevated GH-binding protein (GHBP) serum concentrations. We investigated clinical, genetic and biochemical characteristics of a severely growth-retarded Chinese boy with classical Laron syndrome manifestations.

PATIENTS AND MEASUREMENTS

DNA and mRNA from blood cells of the patient and 11 family members were investigated for GHR mutations. Basal GH, GHBP, IGF-1 and IGFBP-3 concentrations were determined in serum samples. The impact of the aberrant mRNA on GHR protein expression and secretion was analysed in vitro by transfection studies in HEK293 cells.

RESULTS

The proband and seven relatives had excessively elevated GHBP serum concentration. Basal GH in these individuals was significantly greater compared with family members with normal GHBP. The GHBP increase originated from a novel GHR intragenic deletion comprising parts of exon and intron 8 that caused exon 8 skipping from the GHR mRNA transcript. Transfection studies revealed that the predicted loss of plasma membrane anchorage results in direct secretion of the mutant GHR.

CONCLUSIONS

The partial GHR deletion causes excessively elevated GHBP serum concentrations regardless of the state of zygosity of the mutation. The increase in GHBP is associated with significantly elevated basal GH levels. Clinically, only homozygous carriers exhibit classical GHI manifestations. The truncated GHR protein resulting from exon 8 skipping is directly secreted out of the cell.

Evidence for a continuum of genetic, phenotypic, and biochemical abnormalities in children with growth hormone insensitivity

GH insensitivity (GHI) presents in childhood as growth failure and in its severe form is associated with dysmorphic and metabolic abnormalities. GHI may be caused by genetic defects in the GH-IGF-I axis or by acquired states such as chronic illness. This article discusses the former category. The field of GHI due to mutations affecting GH action has evolved considerably since the original description of the extreme phenotype related to homozygous GH receptor (GHR) mutations over 40 yr ago. A continuum of genetic, phenotypic, and biochemical abnormalities can be defined associated with clinically relevant defects in linear growth. The role and mechanisms of the GH-IGF-I axis in normal human growth is discussed, followed by descriptions of mutations in GHR, STAT5B, PTPN11, IGF1, IGFALS, IGF1R, and GH1 defects causing bioinactive GH or anti-GH antibodies. These defects are associated with a range of genetic, clinical, and hormonal characteristics. Genetic abnormalities causing growth failure that is less severe than the extreme phenotype are emphasized, together with an analysis of height and serum IGF-I across the spectrum of different types of GHR defects. An overall view of genotype and phenotype relationships is presented, together with an updated approach to the assessment of the patient with GHI, focusing on investigation of the GH-IGF-I axis and relevant molecular studies contributing to this diagnosis.

Population mutation scanning of human GHR by meltMADGE and identification of a paucimorphic variant

Current studies of human genetic diversity are focused in two areas: first, detection of rare mutations in highly selected clinical cases; and second, in common single-nucleotide polymorphism (SNP) and haplotype effects in the general population. Less frequent SNPs and "paucimorphisms" remain underexplored, although lower frequency coding SNPs are more likely to have functional impact. We have developed a cost-efficient mutation scanning technology, meltMADGE, for population mutation scanning. Previous research in GHR has explored its role in extreme (-3 SD) growth retardation and, subsequently, "moderate" (-2 SD) growth retardation cases. Here, we describe meltMADGE assays for the entire coding region of GHR. As a first step we have established long polymerase chain reaction subbanks for GHR from 2423 unselected subjects and have applied meltMADGE scanning assays of exons 4 and 5 to these subbanks. A novel paucimorphism present at 439+30A>C (allele frequency: 0.0021) in intron 5 (location chr5:42,695,221 in GRCh37/hg19) was identified in 10 individuals, confirmed by sequencing and analysis made for major phenotypic effects. This approach is relevant to the deep sampling of populations for less frequent sequence diversity, some of which is expected to exert significant phenotypic effects.

Novel growth hormone receptor gene mutation in a patient with Laron syndrome

Growth Hormone (GH) is a 22 kDa protein that has effects on growth and glucose and fat metabolisms. These effects are initiated by binding of growth hormone (GH) to growth hormone receptors (GHR) expressed in target cells. Mutations or deletions in the growth hormone receptor cause an autosomal disorder called Laron-type dwarfism (LS) characterized by high circulating levels of serum GH and low levels of insulin like growth factor-1 (IGF-1). We analyzed the GHR gene for genetic defect in seven patients identified as Laron type dwarfism. We identified two missense mutations (S40L and W104R), and four polymorphisms (S473S, L526I, G168G and exon 3 deletion). We are reporting a mutation (W104R) at exon 5 of GHR gene that is not previously reported, and it is a novel mutation.

Daily energy balance in growth hormone receptor/binding protein (GHR -/-) gene-disrupted mice is achieved through an increase in dark-phase energy efficiency

The goal of this study was to examine factors that contribute to energy balance in female GHR -/- mice. We measured energy intake, energy expenditure (EE), fuel utilization, body mass (M(b)) changes and physical activity in 17month-old female GHR -/- mice and their age-matched wild type littermates. The GHR -/- mice were smaller, consumed more food per unit M(b), had greater EE per unit M(b) and had an increase in 24-h EE/M(b) that was similar to the increase in their surface-area-to-volume ratio. Locomotor activity (LMA) was reduced in the GHR -/- mice, but the energetic cost associated with their LMA was greater than in wild type controls. Furthermore, M(b) and LMA were independent explanatory covariates of most of the variance in EE, and when adjusted for M(b) and LMA, the GHR -/- mice had higher EE during both the light and dark phases of the daily cycle. Respiratory quotient was lower in GHR -/- mice during the light phase, which indicated a greater utilization of lipid relative to carbohydrate in these mice. Additionally, GHR -/- mice had higher ratios of caloric intake to EE at several intervals during the dark phase, and this effect was greater and more sustained in the final 3h of the dark phase. Therefore, we conclude that GHR -/- mice are able to overcome the substantial energetic challenges of dwarfism through several mechanisms that promote stable M(b). Relative to wild type mice, the GHR -/- mice consumed more calories per unit M(b), which offset the disproportionate increase in their daily energy expenditure. While GHR -/- mice oxidized a greater proportion of lipid during the light phase in order to meet their energy requirements, they achieved greater energy efficiency and storage during the dark phase through a combination of higher energy consumption and lower LMA.

Novel nonsense mutation (p.Y113X) in the human growth hormone receptor gene in a Brazilian patient with Laron syndrome

BACKGROUND: To date, about sixty different mutations within GH receptor (GHR) gene have been described in patients with GH insensitivity syndrome (GHI). In this report, we described a novel nonsense mutation of GHR. METHODS: The patient was evaluated at the age of 6 yr, for short stature associated to clinical phenotype of GHI. GH, IGF-1, and GHBP levels were determined. The PCR products from exons 2-10 were sequenced. RESULTS: The patient had high GH (26 µg/L), low IGF-1 (22.5 ng/ml) and undetectable GHBP levels. The sequencing of GHR exon 5 disclosed adenine duplication at nucleotide 338 of GHR coding sequence (c.338dupA) in homozygous state. CONCLUSION: We described a novel mutation that causes a truncated GHR and a loss of receptor function due to the lack of amino acids comprising the transmembrane and intracellular regions of GHR protein, leading to GHI.

A novel growth hormone receptor gene deletion mutation in a patient with primary growth hormone insensitivity syndrome (Laron syndrome)

OBJECTIVE

Growth hormone (GH) insensitivity syndrome (Laron syndrome) is known to be caused by genetic disorders of the GH-IGF-1 axis. Although many mutations in the GH receptor have been identified, there have been only a few reports of deletions of the GH receptor gene.

DESIGN

A Japanese adult female patient with Laron syndrome was subjected to chromosome analysis with basic G-banding and also with a high accuracy technique. Each exon of the GH receptor gene was amplified by means of PCR. Since this patient was diagnosed with osteoporosis, the effects of alendronate on bone mineral density (BMD) were also examined.

RESULTS

The chromosome analysis with the high accuracy technique demonstrated a large deletion of the short arm in one allele of chromosome 5 from p11 to p13.1 [46, XX, del (5) (p11-p13.1)]. PCR amplification of exons of the GH receptor gene showed that only exons 2 and 3 were amplified. Low-dose IGF-1 administration (30microg/kg body weight) failed to increase her BMD, whereas alendronate administration resulted in an increase associated with a decrease in urinary deoxypyridinoline (DPD) and serum osteocalcin concentrations.

CONCLUSIONS

The GH receptor gene of the patient was shown to lack exons 4-10. To the best of our knowledge, this is the third case report of Laron syndrome with large GH receptor deletion. Alendronate was effective for the enhancement of BMD.

Endocrine assessment, molecular characterization and treatment of growth hormone insensitivity disorders

Advances in the diagnosis and treatment of growth hormone insensitivity disorders have occurred in the past 15 years. We discuss the current status of endocrine and molecular evaluation, focusing on the pediatric age range. All the identified mutations of the growth hormone receptor are included. Treatment with recombinant human insulin-like growth factor (rhIGF) 1 in classical cases is summarized and new targets for treatment are discussed, together with therapy using the complex formed between rhIGF1 and rhIGF-binding protein 3.

Diagnostic and therapeutic advances in growth hormone insensitivity

Diagnostic and therapeutic advances in growth hormone insensitivity (GHI) have occurred principally in two areas: the molecular characterization of patients with GHI and treatment with recombinant human insulin like growth factor-I (IGF-I). This article discusses the current status of molecular diagnosis across the spectrum of the disorder. Treatment with recombinant human IGF-I in classical cases is summarized, and potential new targets for treatment are discussed together with the potential for therapy using the newly developed compound recombinant human IGF-I/IGF binding protein-3.

Genetic characterization of growth hormone deficiency and resistance: implications for treatment with recombinant growth hormone

Growth failure can be caused by deficient growth hormone production or action. The genes involved in pituitary development, somatotrope function, as well as growth hormone synthesis, secretion, and action have recently been characterized in considerable detail. Familial growth failure has played an important role in identifying these genes, and a large number of mutations adversely affecting the development and function of the growth hormone/insulin-like growth factor axis have been discovered. Inactivating mutations leading to growth retardation in humans have been identified in several pituitary transcription factor genes (HESX1, PITX2, LHX3, PROP1, POU1F1) as well as in genes encoding the growth hormone-releasing hormone receptor (GHRH-R), the G(s) protein alpha subunit (GNAS1), growth hormone itself (GH-1), the growth hormone receptor (GHR), and in a single case each, the insulin-like growth factor I (IGF-I) and the IGF-I receptor. Mutations in pituitary transcription factors cause developmental abnormalities of the pituitary and deficiency of multiple pituitary hormones [growth hormone (GH), prolactin (Prl), thyrotropin (TSH) and lutropin/follitropin (LH/FSH)]. Most of the syndromes respond well to therapy with recombinant GH; exceptions are antibody-mediated resistance in GHD type IA (not all patients) and cases of Laron syndrome (GHR deficiency). Such patients respond to IGF-I therapy. This review summarizes the molecular genetics, functional defects, phenotypes, diagnostic considerations and therapeutic aspects of syndromes associated with mutations in the relevant genes.

Multi-exon deletions of the FBN1 gene in Marfan syndrome

BACKGROUND

Mutations in the fibrillin -1 gene (FBN1) cause Marfan syndrome (MFS), an autosomal dominant multi-system connective tissue disorder. The 200 different mutations reported in the 235 kb, 65 exon-containing gene include only one family with a genomic multi-exon deletion.

METHODS

We used long-range RT-PCR for mutation detection and long-range genomic PCR and DNA sequencing for identification of deletion breakpoints, allele-specific transcript analyses to determine stability of the mutant RNA, and pulse-chase studies to quantitate fibrillin synthesis and extracellular matrix deposition in cultured fibroblasts. Southern blots of genomic DNA were probed with three overlapping fragments covering the FBN1 coding exons

RESULTS

Two novel multi-exon FBN1 deletions were discovered. Identical nucleotide pentamers were found at or near the intronic breakpoints. In a Case with classic MFS, an in-frame deletion of exons 42 and 43 removed the C-terminal 24 amino acids of the 5th LTBP (8-cysteine) domain and the adjacent 25th calcium-binding EGF-like (6-cysteine) domain. The mutant mRNA was stable, but fibrillin synthesis and matrix deposition were significantly reduced. A Case with severe childhood-onset MFS has a de novo deletion of exons 44-46 that removed three EGF-like domains. Fibrillin protein synthesis was normal, but matrix deposition was strikingly reduced. No genomic rearrangements were detected by Southern analysis of 18 unrelated MFS samples negative for FBN1 mutation screening.

CONCLUSIONS

Two novel deletion cases expand knowledge of mutational mechanisms and genotype/phenotype correlations of fibrillinopathies. Deletions or mutations affecting an LTBP domain may result in unstable mutant protein cleavage products that interfere with microfibril assembly.

The legacy of pharmacogenetics and potential applications

Some 40 years of pharmacogenetic research indicates that knowledge of human genetic diversity is essential to a broader understanding of variation in human drug response, and suggests that drug therapy tailored to the genetic characteristics of the individual may be a realistic goal. Aided by new technologies, molecular studies of genetic polymorphisms of many human enzymes, receptors, and other proteins indicate that only a limited number of important protein variants account for the diversity in drug response, raising the prospect that these variants may be cataloged relatively soon for many human populations. The next great challenge of pharmacogenetics is to pin down the cellular location and effect of these variant proteins on the pathways and networks that govern individual variation in responses to drugs and other exogenous chemicals. In this paper, we will discuss some the current challenges to progress in pharmacogenetics and newer strategies that might be used to improve prospects of drug design and personalized therapy.