Absence of GH-releasing hormone (GHRH) mutations in selected patients with isolated GH deficiency

Identification and functional analysis of first heterozygous frameshift mutation in the GHRH gene in a Chinese boy with isolated growth hormone deficiency

BACKGROUND

Isolated growth hormone deficiency (IGHD) is a rare genetically heterogeneous disorder caused primarily by mutations in GH1 and GH releasing hormone receptor (GHRHR). The aim of this study was to identify the molecular etiology of a Chinese boy with IGHD.

METHODS

Whole-exome sequencing, sanger sequencing and bioinformatic analysis were performed to screen for candidate mutations. The impacts of candidate mutation on gene expression, intracellular localization and protein function were further evaluated by in vitro assays.

RESULTS

A novel heterozygous frameshift mutation in the GHRH gene (c.91dupC, p.R31Pfs*98) was identified in a Chinese boy clinically diagnosed as having IGHD. The mutation was absent in multiple public databases, and considered as deleterious using in silico prediction, conservative analysis and three-dimensional homology modeling. Furthermore, mRNA and protein expression levels of mutant GHRH were significantly increased than wild-type GHRH (p < 0.05). Moreover, mutant GHRH showed an aberrant accumulation within the cytoplasm, and obviously reduced ability to stimulate GH secretion and cAMP accumulation in human GHRHR-expressing pituitary GH3 cells compared to wild-type GHRH (p < 0.05).

CONCLUSION

Our study discovered the first loss-of function mutation of GHRH in a Chinese boy with IGHD and provided new insights on IGHD pathogenesis caused by GHRH haploinsufficiency.

Models of GH deficiency in animal studies

Growth hormone (GH) is a peptide hormone released from pituitary somatotrope cells that promotes growth, cell division and regeneration by acting directly through the GH receptor (GHR), or indirectly via hepatic insulin-like growth factor 1 (IGF1) production. GH deficiency (GHD) can cause severe consequences, such as growth failure, changes in body composition and altered insulin sensitivity, depending of the origin, time of onset (childhood or adulthood) or duration of GHD. The highly variable clinical phenotypes of GHD can now be better understood through research on transgenic and naturally-occurring animal models, which are widely employed to investigate the origin, phenotype, and consequences of GHD, and particularly the underlying mechanisms of metabolic disorders associated to GHD. Here, we reviewed the most salient aspects of GH biology, from somatotrope development to GH actions, linked to certain GHD types, as well as the animal models employed to reproduce these GHD-associated alterations.

Growth, development, puberty and adult height before and during treatment in children with congenital isolated growth hormone deficiency

OBJECTIVE

To describe the growth, development and puberty in children with congenital IGHD before and during hGH treatment.

SUBJECTS

Patients with cIGHD treated by hGH between the years 1958-1992.

SETTING

All patients were diagnosed, treated and followed in our clinic.

PARTICIPANTS

Data were found in 37/41 patients (21 m, 16 f). 34 had hGH-1A deletions, 7 GHRH-R mutations. Patients, referred after age 25, were excluded.

RESULTS

The birth length of 10/37 neonates was 48.29±2.26 (44-50) cm. Birth weight of 28/37 neonates was 3380±370 g (m), 3230±409 g (f). Neuromotor milestones were variable. Age at referral was 5.7±4.2 y (m) and 5.6±3.8 y (f). Initiation of hGH treatment (35μg/kg/d) was 7.5±4.8, (0.8-15.08) y (m) and 6.8±4.36 (0.8-16.5) y (f). Height SDS increased from -4.3 to -1.8 (m) and from -4.5 to -2.6 (f). Head circumference increased from -2.6 to -1.3 (m) and from -2.7 to -2.3 (f). BMI increased from 15.8 to 20.6 (m) and from 15.5 to 20.4 (f). There was a negative correlation between age of hGH initiation and change in height SDS (r=-0.66; ρ<0.01), same for bone age (r=-0.69; ρ<0.01). Upper/lower body ratio decreased from 2.5±2.1 (m±SD) to 1.08±0.1 (ρ<0.0005). Puberty was delayed in boys, less so in girls. Mean age of 1st ejaculation (14 m) was 17.6±2.2 y and of menarche (14 f. was 13.7±1.2 y. In both genders there was a positive correlation between age at start of hGH and age at onset of puberty (r=0.57; ρ<0.01). All reached full sexual development but the penile and testicular sizes were below normal. There was a positive correlation between length of hGH treatment and final testicular volume (r=0.597, ρ=0.05) and a negative correlation between the age at initiation of hGH treatment and final testicular volume(r=-0.523, ρ=0.018). All were obese and hGH treatment increased the adiposity progressively (r=0.418, ρ=0.013).

CONCLUSION

Early diagnosis and treatment of cIGHD enables normal or near normal growth, development and puberty.

Molecular screening of a large cohort of Moroccan patients with congenital hypopituitarism

BACKGROUND/OBJECTIVES

Congenital hypopituitarism is a rare disease which, for most patients, has no identified molecular cause. We aimed to document the molecular basis of growth retardation in a Moroccan cohort.

DESIGN/PATIENTS

80 index cases [54 with isolated growth hormone deficiency (IGHD), 26 with combined pituitary hormone deficiency (CPHD)] were screened for molecular defects in GH1 (including LCR-GH1), GHRHR, GHSR, GHRH, PROP1, POU1F1, HESX1, LHX3, LHX4 and SOX3.

RESULTS

Five different deleterious mutations were identified in 14 patients from eight families. In the IGHD group, three genes were found to be involved: GH1, GHRHR and GHSR. In the CPHD group, PROP1 was the only mutated gene. In addition, two heterozygous variations whose deleterious effect remains to be demonstrated were identified (in GH1 and LHX4), and two polymorphisms (missense variations) were detected (in LHX3 and in GHSR). The prevalence of mutations in this Moroccan GHD cohort was 10% (8/80), 11·1% (6/54) in the IGHD group and 7·7% (2/26) in the CPHD group.

CONCLUSION

This is the first molecular screening of congenital GHD in a Moroccan population and, like other studies, mutations were preferentially identified in familial cases (75%); mutations in genes such as POU1F1, HESX1, SOX3, LHX3 and LHX4 are extremely rare. The p.R73C PROP1 mutation was the most frequent mutation in CPHD; this should be the first one to screen in this population. Our results should contribute to a better diagnosis and management of this heterogeneous disease condition.

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.

Height gain at adult-height age in 184 short patients treated with growth hormone from prepubertal age to near adult-height age is not related to GH secretory status at GH therapy onset

BACKGROUND

GH release after stimuli classifies short children as severe idiopathic isolated GH deficiency (IIGHD), mild IIGHD, dissociated GH release (DGHR) and normal GH release (NGHR) and anthropometric birth data as adequate for gestational age (AGA) or small for gestational age (SGA). GH release after stimuli classifies AGA patients as IIGHD or as idiopathic short stature (ISS).

AIM

To compare height gain induced by GH therapy (31.8 ± 3.5 µg/kg/day, 7.7 ± 1.6 years) started at prepubertal age and stopped at near adult-height age.

METHODS

A retrospective longitudinal multicenter study including 184 short patients classified as severe IIGHD n = 25, mild IIGHD n = 75, DGHR n = 55 and NGHR n = 29; or as IIGHD n = 78, ISS n = 57 and SGA n = 49. Height gain was evaluated throughout GH therapy and at adult-height age.

RESULTS

Height-SDS gain at adult-height age was similar among severe IIGHD (1.8 ± 0.8 SDS), mild IIGHD (1.6 ± 0.6 SDS), DGHR (1.7 ± 0.7 SDS) and NGHR (1.6 ± 0.7 SDS), or among IIGHD (1.7 ± 0.7 SDS), ISS (1.7 ± 0.6 SDS) and SGA (1.6 ± 0.8 SD).

CONCLUSION

GH-release stimuli are of little help for deciding on GH therapy in the clinical management of prepubertal children with IIGHD, ISS or SGA.

Relatively high frequency of non-synonymous GLI2 variants in patients with congenital hypopituitarism without holoprosencephaly

OBJECTIVE

GLI2 is a downstream transcription factor in Sonic Hedgehog signalling, acting early in ventral forebrain and pituitary development. Heterozygous nonsense GLI2 mutations have been reported in patients with isolated or combined pituitary hormone deficiency (CPHD), with or without holoprosencephaly. The aim of this study was to screen for GLI2 mutations in a large cohort of patients with congenital GH deficiency.

DESIGN AND PATIENTS

The GLI2 coding region of 41 patients with severe isolated GH deficiency (IGHD) and 136 patients with CPHD was amplified by PCR using intronic primers and sequenced. The frequency of GLI2 variants was verified in up to 155 Brazilian controls and in the 1000 Genomes database. The consequences of allelic variants were analysed by the Polyphen, SIFT, Mutationtaster and SNAP prediction sites.

RESULTS

Eighteen different heterozygous non-synonymous GLI2 variants were identified in 24 patients. Twenty-three patients had CPHD and one had IGHD. Two patients had additional diabetes insipidus, indicating deficiencies of anterior and posterior pituitary lobes. The posterior pituitary lobe on MRI was ectopic in 16, not visible in 4, normally placed in 2 and imaging was not available in two patients, but there were no signs of holoprosencephaly. Sixteen GLI2 variants were considered deleterious in at least one of the prediction sites.

CONCLUSIONS

A relatively high frequency of non-synonymous GLI2 variants was identified in patients with congenital GH deficiency without other brain defects, and most of these patients presented with CPHD and an ectopic posterior pituitary lobe. In vitro functional assays may contribute to ascertain the deleterious consequences of these variants.

Contribution of human growth hormone-releasing hormone receptor (GHRHR) gene sequence variation to isolated severe growth hormone deficiency (ISGHD) and normal adult height

OBJECTIVE

Molecular causes of isolated severe growth hormone deficiency (ISGHD) in several genes have been established. The aim of this study was to analyse the contribution of growth hormone-releasing hormone receptor (GHRHR) gene sequence variation to GH deficiency in a series of prepubertal ISGHD patients and to normal adult height.

DESIGN, SUBJECTS AND MEASUREMENTS

A systematic GHRHR gene sequence analysis was performed in 69 ISGHD patients and 60 normal adult height controls (NAHC). Four GHRHR single-nucleotide polymorphisms (SNPs) were genotyped in 248 additional NAHC. An analysis was performed on individual SNPs and combined genotype associations with diagnosis in ISGHD patients and with height-SDS in NAHC.

RESULTS

Twenty-one SNPs were found. P3, P13, P15 and P20 had not been previously described. Patients and controls shared 12 SNPs (P1, P2, P4-P11, P16 and P21). Significantly different frequencies of the heterozygous genotype and alternate allele were detected in P9 (exon 4, rs4988498) and P12 (intron 6, rs35609199); P9 heterozygous genotype frequencies were similar in patients and the shortest control group (heights between -2 and -1 SDS) and significantly different in controls (heights between -1 and +2 SDS). GHRHR P9 together with 4 GH1 SNP genotypes contributed to 6·2% of height-SDS variation in the entire 308 NAHC.

CONCLUSIONS

This study established the GHRHR gene sequence variation map in ISGHD patients and NAHC. No evidence of GHRHR mutation contribution to ISGHD was found in this population, although P9 and P12 SNP frequencies were significantly different between ISGHD and NAHC. Thus, the gene sequence may contribute to normal adult height, as demonstrated in NAHC.

Diagnosis of growth hormone deficiency in childhood

PURPOSE OF REVIEW

The diagnosis of growth hormone deficiency (GHD) in childhood is challenging, in large part because of the lack of a true gold standard and the relatively poor performance of available diagnostic testing. This review discusses the recent literature on this topic.

RECENT FINDINGS

Auxology and clinical judgment remain the foundation for the diagnosis of GHD. Provocative growth hormone testing is poorly reproducible, dependent on factors such as body composition and pubertal status, and further limited by significant variability among commercially available growth hormone assays. Measurement of insulin-like growth factor I and insulin-like growth factor-binding protein 3 is not diagnostically useful in isolation but is helpful in combination with other diagnostic measures. Neuroimaging is also useful to inform diagnosis, as pituitary abnormalities suggest a higher likelihood of GHD persisting into adulthood. Although genetic testing is not routinely performed in the diagnosis of GHD at the present time, multiple recent reports raise the possibility that it may play a more important role in diagnosing GHD in the future.

SUMMARY

Beyond physicians' integrated assessment of auxology, clinical presentation, and bone age, current tools to diagnose GHD are suboptimal. Recent literature emphasizes the need to reappraise our current practice and to consider new tools for diagnosis.