Detection of a recurring mutation in the human growth hormone-releasing hormone receptor gene

Genetic spectrum and predictors of mutations in four known genes in Asian Indian patients with growth hormone deficiency and orthotopic posterior pituitary: an emphasis on regional genetic diversity

CONTEXT

Regional variation in prevalence of genetic mutations in growth hormone deficiency (GHD) is known.

AIM

Study phenotype and prevalence of mutations in GH1, GHRHR, POU1F1, PROP1 genes in GHD cohort.

METHODS

One hundred and two patients {Isolated GHD (IGHD): 79; combined pituitary hormone deficiency (CPHD): 23} with orthotopic posterior pituitary were included. Auxologic, hormonal and radiological details were studied. All four genes were analysed in IGHD patients. POU1F1 and PROP1 were studied in CPHD patients.

RESULTS

Of 102, 19.6% were familial cases. Height SDS, mean (SD) was - 5.14 (1.63). Peak GH, median (range) was 0.47 ng/ml (0-6.59), 72.5% patients had anterior pituitary hypoplasia (APH). Twenty mutations (novel: 11) were found in 43.1% patients (n = 44, IGHD-36, CPHD-8). GHRHR mutations (n = 32, p.Glu72* = 24) were more common than GH1 mutations (n = 4) in IGHD cohort. POU1F1 mutations (n = 6) were more common than PROP1 mutations (n = 2) in CPHD cohort. With few exceptions, this prevalence pattern is contrary to most studies in world-literature. No patients with peak GH > 4 ng/ml had mutations, signifying it as negative predictor. While many parameters were significant on univariate analysis, only positive family history and lower median peak GH levels were significant predictors of mutations on multivariate analysis in IGHD patients.

CONCLUSION

At variance with world literature, we found reverse predominance of GHRHR over GH1 mutations, POU1F1 over PROP1 mutations and predominance of GHRHR p.Glu72* mutations thus re-affirming the regional diversity in GHD genetics. We report positive and negative predictors of mutations in GHD.

Growth hormone deficiency with advanced bone age: phenotypic interaction between GHRH receptor and CYP21A2 mutations diagnosed by sanger and whole exome sequencing

Isolated growth hormone deficiency (IGHD) is the most common pituitary hormone deficiency and, clinically, patients have delayed bone age. High sequence similarity between CYP21A2 gene and CYP21A1P pseudogene poses difficulties for exome sequencing interpretation. A 7.5 year-old boy born to second-degree cousins presented with severe short stature (height SDS -3.7) and bone age of 6 years. Clonidine and combined pituitary stimulation tests revealed GH deficiency. Pituitary MRI was normal. The patient was successfully treated with rGH. Surprisingly, at 10.8 years, his bone age had advanced to 13 years, but physical exam, LH and testosterone levels remained prepubertal. An ACTH stimulation test disclosed a non-classic congenital adrenal hyperplasia due to 21-hydroxylase deficiency explaining the bone age advancement and, therefore, treatment with cortisone acetate was added. The genetic diagnosis of a homozygous mutation in GHRHR (p.Leu144His), a homozygous CYP21A2 mutation (p.Val282Leu) and CYP21A1P pseudogene duplication was established by Sanger sequencing, MLPA and whole-exome sequencing. We report the unusual clinical presentation of a patient born to consanguineous parents with two recessive endocrine diseases: non-classic congenital adrenal hyperplasia modifying the classical GH deficiency phenotype. We used a method of paired read mapping aided by neighbouring mis-matches to overcome the challenges of exome-sequencing in the presence of a pseudogene.

Genetic causes of isolated and combined pituitary hormone deficiency

Research over the last 20 years has led to the elucidation of the genetic aetiologies of Isolated Growth Hormone Deficiency (IGHD) and Combined Pituitary Hormone Deficiency (CPHD). The pituitary plays a central role in growth regulation, coordinating the multitude of central and peripheral signals to maintain the body's internal balance. Naturally occurring mutation in humans and in mice have demonstrated a role for several factors in the aetiology of IGHD/CPHD. Mutations in the GH1 and GHRHR genes shed light on the phenotype and pathogenesis of IGHD whereas mutations in transcription factors such as HESX1, PROP1, POU1F1, LHX3, LHX4, GLI2 and SOX3 contributed to the understanding of CPHD. Depending upon the expression patterns of these molecules, the phenotype may consist of isolated hypopituitarism, or more complex disorders such as septo-optic dysplasia (SOD) and holoprosencephaly. Although numerous monogenic causes of growth disorders have been identified, most of the patients with IGHD/CPHD remain with an explained aetiology as shown by the relatively low mutation detection rate. The introduction of novel diagnostic approaches is now leading to the disclosure of novel genetic causes in disorders characterized by pituitary hormone defects.

Partial Loss of Function of the GHRH Receptor Leads to Mild Growth Hormone Deficiency

OBJECTIVE

Recessive mutations in GHRHR are associated with severe isolated growth hormone deficiency (IGHD), with a final height in untreated patients of 130 cm ± 10 cm (-7.2 ± 1.6 SDS; males) and 114 ± 0.7 cm (-8.3 ± 0.1 SDS; females).

DESIGN

We hypothesized that a consanguineous Pakistani family with IGHD in three siblings (two males, one female) would have mutations in GH1 or GHRHR.

RESULTS

Two novel homozygous missense variants [c.11G>A (p.R4Q), c.236C>T (p.P79L)] at conserved residues were identified in all three siblings. Both were absent from control databases, aside from pR4Q appearing once in heterozygous form in the Exome Aggregation Consortium Browser. The brothers were diagnosed with GH deficiency at 9.8 and 6.0 years (height SDS: -2.24 and -1.23, respectively), with a peak GH of 2.9 μg/liter with low IGF-1/IGF binding protein 3. Their sister presented at 16 years with classic GH deficiency (peak GH <0.1 μg/liter, IGF-1 <3.3 mmol/liter) and attained an untreated near-adult height of 144 cm (-3.0 SDS); the tallest untreated patient with GHRHR mutations reported. An unrelated Pakistani female IGHD patient was also compound homozygous. All patients had a small anterior pituitary on magnetic resonance imaging. Functional analysis revealed a 50% reduction in maximal cAMP response to stimulation with GHRH by the p.R4Q/p.P79L double mutant receptor, with a 100-fold increase in EC50.

CONCLUSION

We report the first coexistence of two novel compound homozygous GHRHR variants in two unrelated pedigrees associated with a partial loss of function. Surprisingly, the patients have a relatively mild IGHD phenotype. Analysis revealed that the pP79L mutation is associated with the compromise in function, with the residual partial activity explaining the mild phenotype.

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.

Isolated growth hormone deficiency (GHD) in childhood and adolescence: recent advances

The diagnosis of GH deficiency (GHD) in childhood is a multistep process involving clinical history, examination with detailed auxology, biochemical testing, and pituitary imaging, with an increasing contribution from genetics in patients with congenital GHD. Our increasing understanding of the factors involved in the development of somatotropes and the dynamic function of the somatotrope network may explain, at least in part, the development and progression of childhood GHD in different age groups. With respect to the genetic etiology of isolated GHD (IGHD), mutations in known genes such as those encoding GH (GH1), GHRH receptor (GHRHR), or transcription factors involved in pituitary development, are identified in a relatively small percentage of patients suggesting the involvement of other, yet unidentified, factors. Genome-wide association studies point toward an increasing number of genes involved in the control of growth, but their role in the etiology of IGHD remains unknown. Despite the many years of research in the area of GHD, there are still controversies on the etiology, diagnosis, and management of IGHD in children. Recent data suggest that childhood IGHD may have a wider impact on the health and neurodevelopment of children, but it is yet unknown to what extent treatment with recombinant human GH can reverse this effect. Finally, the safety of recombinant human GH is currently the subject of much debate and research, and it is clear that long-term controlled studies are needed to clarify the consequences of childhood IGHD and the long-term safety of its treatment.

Novel compound heterozygous mutations of the growth hormone-releasing hormone receptor gene in a case of isolated growth hormone deficiency

OBJECTIVE

To elucidate the pathogenesis of isolated growth hormone (GH) deficiency in a Japanese girl without consanguinity.

DESIGN

A 2-year-old girl of height 77.2 cm (-3.0 SD for Japanese girls) was found to have an insulin-like growth factor (IGF)-1 level of 7 ng/mL and IGF binding protein-3 (IGFBP-3) level of 0.41 μg/mL. GH responded modestly to a series of pharmacological stimulants, increasing to 2.81 ng/mL with insulin-induced hypoglycemia, 3.78 ng/mL with arginine, and 3.93 with GH-releasing hormone (GHRH). Following direct sequencing of the GHRH receptor (GHRHR) gene, evaluation by the luciferase reporter assay, immunofluorescence study, and in vitro splicing assay with minigene constructs was conducted.

RESULTS

Novel compound heterozygous GHRHR gene mutations were identified in the patient. A p.G136V substitution elicited no luciferase activity increment in response to GHRH stimulation, with normal membranous expression. Splicing assay demonstrated that the IVS2+3a>g mutation would lead to aberrant splicing.

CONCLUSIONS

A case of isolated GH deficiency due to novel GHRHR gene mutations was identified.

Identification and functional analysis of novel human growth hormone-releasing hormone receptor (GHRHR) gene mutations in Japanese subjects with short stature

CONTEXT

Growth hormone-releasing hormone receptor (GHRHR) gene mutations have been identified in patients of different ethnic origins with isolated GH deficiency (IGHD) type IB. However, the prevalence of these mutations in the Japanese population has yet to be fully determined.

OBJECTIVES

This study aimed to evaluate the contributions of GHRHR mutations to the molecular mechanism underlying short stature in Japanese subjects.

DESIGN

The GHRHR gene was sequenced in 127 unrelated Japanese patients with either IGHD (n = 14) or idiopathic short stature (ISS; n = 113). Sequence variants were evaluated in family members and 188 controls, and then examined in functional studies.

RESULTS

A novel homozygous E382E (c.1146G>A) synonymous variant, at the last base of exon 12, was identified in an IGHD family with two affected sisters. In vitro splicing studies showed this mutation to result in skipping of exon 12. In one ISS patient, a heterozygous ATG-166T>C variant was found in the distal Pit-1 P2 binding element of the GHRHR promoter. In two control subjects, a close but distinct variant, ATG-164T>C, was detected. Functional studies showed that both promoter variants diminish promoter activity by altering Pit-1 binding ability. Four missense variants were also found in both patient and control groups but had no detectable functional consequences.

CONCLUSIONS

The homozygous GHRHR mutation was rare, being detected in only one Japanese IGHD family. Future research is needed to clarify the genetic contributions of heterozygous functional promoter variants to GHD, ISS and normal-stature variations.

Genetic causes and treatment of isolated growth hormone deficiency-an update

Isolated growth hormone deficiency is the most common pituitary hormone deficiency and can result from congenital or acquired causes, although the majority of cases are idiopathic with no identifiable etiology. Known genes involved in the genetic etiology of isolated growth hormone deficiency include those that encode growth hormone (GH1), growth-hormone-releasing hormone receptor (GHRHR) and transcription factor SOX3. However, mutations are identified in a relatively small percentage of patients, which suggests that other, yet unidentified, genetic factors are involved. Among the known factors, heterozygous mutations in GH1 remain the most frequent cause of isolated growth hormone deficiency. The identification of mutations has clinical implications for the management of patients with this condition, as individuals with heterozygous GH1 mutations vary in phenotype and can, in some cases, develop additional pituitary hormone deficiencies. Lifelong follow-up of these patients is, therefore, recommended. Further studies in the genetic etiology of isolated growth hormone deficiency will help to elucidate mechanisms implicated in the control of growth and may influence future treatment options. Advances in pharmacogenomics will also optimize the treatment of isolated growth hormone deficiency and other conditions associated with short stature, for which recombinant human growth hormone is a licensed therapy.

A recurrent signal peptide mutation in the growth hormone releasing hormone receptor with defective translocation to the cell surface and isolated growth hormone deficiency

CONTEXT

Mutations in the GHRH receptor (GHRHR) have been detected in the familial type-IB isolated GH deficiency (IGHD-IB) inherited as an autosomal recessive disorder and characterized by a low but detectable serum GH level and good response to substitutive GH therapy.

OBJECTIVE

The aim of our study was the identification of mutations in sporadic patients with a IGHD-IB phenotype.

SUBJECTS AND METHODS

The GHRHR gene was systematically screened by DHPLC in 134 IGHD patients with no family history of the disorder or declared parental consanguinity.

RESULTS

We identified a novel variation, Val10Gly, within the signal peptide at the heterozygous state in three patients and in one of 1084 controls (P = 0.004), suggesting that it might contribute to IGHD. The functional analysis showed that the signal peptide is not cleaved from the mutant GHRHR, which in turn is not translocated to the cellular surface, demonstrating that 10Gly drastically affects the receptor correct processing. Because 10Gly was also present in normal-stature relatives of the patients as well as in a control, it is likely that it exerts its effects in the context of other genetic and environmental susceptibility factors.

CONCLUSION

At difference from previous papers reporting GHRHR mutations in familial cases with a clear recessive mode of inheritance, our study was conducted on a large sample of sporadic patients and allowed to discover a novel mechanism of the disease caused by a recurrent dominant mutation in the GHRHR signal peptide associated with incomplete penetrance.

[Long time consequences of the growth hormone deficiency]

This article describes the long time consequences of the isolated and lifetime growth hormone (GH) deficiency using a single model of GH releasing hormone resistance (GHRH) due to a homozygous mutation in the GHRH receptor gene, in a hundred of subjects. These consequences include severe short stature with final height between -9.6 and -5.2 standard deviations below of the mean, with proportional reductions of the bone dimensions; reduction of the anterior pituitary corrected to cranial volume and the thyroid, the uterus, the spleen and left ventricular mass volume, all corrected to body surface, in contrast of pancreas and liver size, bigger than in controls, when equally corrected. Body composition features included marked reduction in the amount of fat free mass (kg) and increase of fat mass percentage, with predominant abdominal deposit. In the metabolic aspects, we find increase in the total cholesterol and LDL cholesterol; reduction of the insulin and the insulin resistance assessed by Homeostasis model assessment; increase of ultra sensitive C reactive protein and systolic body pressure in adults, although without evidences of premature atherosclerosis. Other findings include smaller bone resistance, although above of the threshold of fractures, delayed puberty, normal fertility, small parity, anticipated climacteric and normal quality of life.

A case with isolated growth hormone deficiency caused by compound heterozygous mutations in GH-1: a novel missense mutation in the initiation codon and a 7.6kb deletion

OBJECTIVE

To characterize the cause of a sporadic isolated growth hormone deficiency in a single patient.

METHODS

Genomic DNA was extracted from blood samples of the patient and his family. Exons and exon-intron junctions of the GH-1 gene were amplified by PCR and sequenced. To characterize possible GH-1 deletions we performed Southern blot analysis and PCR-restriction fragment length analyses.

RESULTS

An adenine to guanine mutation at the first nucleotide of the initiation codon (Met [ATG](-26)Val [GTG]) of the GH-1 gene was identified in the patient and the mother. A 7.6kb GH-1 deletion was identified in the patient, the brother and the father.

CONCLUSION

The patient was a compound heterozygote for an allele bearing a Met(-26)Val missense mutation inherited from his mother and an allele containing deletion of the entire GH-1 gene inherited from his father. The present missense mutation has not been described previously. Attention should be paid to the heterozygous gene deletion that is difficult to detect by PCR-based genetic analysis. The patient responded to GH replacement therapy fairly well, without developing anti-hGH antibody.

Heterozygosity for a mutation in the growth hormone-releasing hormone receptor gene does not influence adult stature, but affects body composition

CONTEXT

Biallelic mutations in the GHRH receptor (GHRHR) gene (GHRHR) are a frequent cause of isolated GH deficiency (IGHD). Although heterozygous carriers of these mutations appear normal, we hypothesized that heterozygosity for a GHRHR mutation might be associated with a subclinical phenotype.

METHODS

We studied members of a large Brazilian kindred with IGHD (Itabaianinha cohort) caused by a homozygous null GHRHR mutation. We compared 76 adult subjects (age, 25-75 yr) heterozygous for the mutation (WT/MT) with 77 sex-matched controls from the same population who are homozygous for the wild-type GHRHR allele (WT/WT).

RESULTS

We found no difference in adult height and sd score for serum IGF-I between the two groups. Body weight, body mass index, skin folds, waist and hip circumferences, and lean mass were all reduced in WT/MT subjects. Percentage fat mass and waist/hip ratio were similar in the two groups. Fasting insulin and homeostasis model assessment of insulin resistance were lower in WT/MT. The other biochemical parameters [total and fractionated cholesterol, triglycerides, lipoprotein (a), and C-reactive protein] were not different between the two groups.

CONCLUSIONS

Heterozygosity for a null GHRHR mutation is not associated with reduction in adult stature or in serum IGF-I but is associated with changes in body composition and possibly an increase in insulin sensitivity. These effects do not seem to be modulated by changes in circulating IGF-I.

A new mutation in the growth hormone-releasing hormone receptor gene in two Israeli Arab families

BACKGROUND

Mutations in the GHRH receptor gene (GHRH-R) are emerging as a common cause of familial isolated GH deficiency (IGHD).

DESIGN

We searched for GHRH-R mutations in 10 patients with IGHD of Israeli-Arab origin, belonging to two highly consanguineous families.

METHODS

Analysis of the 13 coding exons, the intron-exon boundaries, and the proximal promoter of the GHRH-R was performed by denaturing gradient gel electrophoresis. Abnormally migrating bands were sequenced. The newly found mutation was inserted into GHRH-R cDNA. Wild type and mutant receptor were expressed in Chinese hamster ovary (CHO) cells, and the cAMP response to GHRH was measured.

RESULTS

All patients were homozygous for a novel GHRH-R missense mutation in exon 11 that replaces arginine with cysteine (R357C). Functional assay demonstrated complete inactivity of the mutant receptor in vitro. The prevalence of the mutant allele in the Israeli-Arab population was found to be 2%. All the patients had low but detectable GH reserve, proportionate short stature, and growth retardation since early childhood, with good growth response to GH treatment. Magnetic resonance imaging, performed in 3 patients, revealed a normal sized anterior pituitary in one patient evaluated at early childhood, and a borderline hypoplastic gland in the 2 patients evaluated at puberty.

CONCLUSIONS

We describe a novel missense mutation in the GHRH-R. The high incidence of the mutant allele in Israeli Arabs suggests that the mutation may be a common cause of familial IGHD in this population.

Hormônio do crescimento ou somatotrófico: novas perspectivas na deficiência isolada de GH a partir da descrição da mutação no gene do receptor do GHRH nos indivíduos da cidade de Itabaianinha, Brasil

Além de influenciar o crescimento corpóreo, o hormônio do crescimento, ou somatotrófico, desempenha importante papel no metabolismo, composição corporal, perfil lipídico, estado cardiovascular e longevidade. Seu controle é multi-regulado por hormônios, metabólitos e peptídeos hipotalâmicos. Dados sobre a Deficiência Isolada de GH (DIGH) obtidos a partir da descrição da mutação IVS1+1G®A no gene do receptor do hormônio liberador do GH (GHRH-R) em indivíduos da cidade de Itabaianinha, SE, são revisados. São abordadas novas perspectivas sobre o modelo de resistência ao GHRH, a importância do GHRH no controle da secreção de GH, a freqüência das mutações do gene do GHRH-R, a relevância diagnóstica do IGF-I e os achados metabólicos, cardiovasculares e de qualidade de vida nestes indivíduos.

Phenotypic analysis and growth response to different growth hormone treatment schedules in two siblings with an inactivating mutation in the growth hormone-releasing hormone receptor gene

Mutations in the GHRH receptor (GHRHR) gene (GHRHR) are emerging as a common cause of familial isolated growth hormone deficiency (IGHD) type IB. The use of gonadotropin-releasing hormone (GnRH) analogues has been advocated as a tool to delay puberty in patients with isolated GH deficiency (IGHD), allowing longer time for the beneficial effect of exogenous human GH (hGH) treatment on growth. We describe two male siblings with IGHD due to a homozygous missense GHRHR mutation who, because they were started on hGH therapy at different ages, presented with different height SDS at the onset of puberty and therefore had different predicted target heights. The shorter brother was treated with GnRH analogue plus hGH for 3 years, whereas the other brother received only hGH. Despite different predicted heights at the onset of puberty, they attained similar final heights. We conclude that in patients with IGHD, GnRH analogue treatment should be considered to delay puberty and obtain a maximal growth response if hGH treatment is started in late childhood and the predicted height at puberty onset is below the genetic target.

Variability in anterior pituitary size within members of a family with GH deficiency due to a new splice mutation in the GHRH receptor gene

OBJECTIVE

Mutations in the GHRH receptor (GHRHR) gene (GHRHR) cause autosomal recessive isolated GH deficiency (IGHD), and are usually associated with anterior pituitary hypoplasia (APH) (defined as pituitary height more than 2 SDS below normal). We searched for GHRHR mutations and studied pituitary morphology in three prepubertal sibs with severe IGHD, who were born from consanguineous parents.

DESIGN

We sequenced the 13 exons and the intron-exon boundaries of the GHRHR of the index patient. After identifying a novel mutation, we sequenced the same area in the other family members. In addition, we performed magnetic resonance imaging (MRI) study of the pituitary (at age 8, 4 and 3 years) in the three affected subjects.

RESULTS

The three children were homozygous for a new GHRHR mutation that alters the second base of the invariant 5' splice site (GT) of intron 12 [IVS12 + 2T-->A]. The parents and an unaffected sibling were heterozygous for the same change. MRI did not show frank APH (by height criteria) in any of the subjects: pituitary height was normal (5.6 mm, +1.8 SDS) in the oldest sibling, and it was low but not below 2 SDS by age-adjusted criteria in the second (3 mm, -1.4 SDS), and third sibling (2.8 mm, -1.7 SDS). Calculated pituitary volume was below -2 SDS in the youngest patient.

CONCLUSIONS

These data demonstrate that pituitary height may fall within 2 SDS from the norm in patients with severe IGHD due to a homozygous GHRHR mutation, and that pituitary size may vary within patients with identical mutations who belong to the same family.

Familial Growth Hormone Deficiency and Mutations in the GHRH Receptor Gene

Growth hormone (GH)-releasing hormone (GHRH) is necessary for the proliferation of the somatotropic cells of the anterior pituitary and the synthesis and secretion of GH. GHRH is released by the hypothalamus into the portal hypophysial circulation to bind to a membrane surface receptor [GHRH receptor (GHRHR)] expressed by the somatotropic cells. Because of the need of GHRH for GH secretion, it is to be expected that alterations in synthesis or action of GHRH would result in isolated GH deficiency (IGHD). Indeed, although GHRH gene mutations have never been reported, mutations in the GHRHR gene (GHRHR) are emerging as a relatively common cause of inherited autosomal recessive IGHD. The first human GHRHR mutations were discovered in families with a history of parental consanguinity. More recently, kindreds in which IGHD subjects are compound heterozygotes for two distinct mutations indicate that faulty GHRHR alleles may be prevalent and that these mutations may need to be suspected even in sporadic IGHD cases. Patients with two faulty GHRHR alleles have normal weight at birth. Growth failure becomes apparent during the first year of life. Biochemical studies show low serum insulin-like growth factor-1 level, and absent or markedly reduced GH response to a variety of stimuli. Magnetic resonance imaging shows hypoplasia of the anterior pituitary. In this chapter, we describe the GHRHR mutations reported to date and the phenotype of affected individuals.