Mutations in the growth hormone releasing hormone receptor: a new form of dwarfism in humans

The role of GPCRs in bone diseases and dysfunctions

The superfamily of G protein-coupled receptors (GPCRs) contains immense structural and functional diversity and mediates a myriad of biological processes upon activation by various extracellular signals. Critical roles of GPCRs have been established in bone development, remodeling, and disease. Multiple human GPCR mutations impair bone development or metabolism, resulting in osteopathologies. Here we summarize the disease phenotypes and dysfunctions caused by GPCR gene mutations in humans as well as by deletion in animals. To date, 92 receptors (5 glutamate family, 67 rhodopsin family, 5 adhesion, 4 frizzled/taste2 family, 5 secretin family, and 6 other 7TM receptors) have been associated with bone diseases and dysfunctions (36 in humans and 72 in animals). By analyzing data from these 92 GPCRs, we found that mutation or deletion of different individual GPCRs could induce similar bone diseases or dysfunctions, and the same individual GPCR mutation or deletion could induce different bone diseases or dysfunctions in different populations or animal models. Data from human diseases or dysfunctions identified 19 genes whose mutation was associated with human BMD: 9 genes each for human height and osteoporosis; 4 genes each for human osteoarthritis (OA) and fracture risk; and 2 genes each for adolescent idiopathic scoliosis (AIS), periodontitis, osteosarcoma growth, and tooth development. Reports from gene knockout animals found 40 GPCRs whose deficiency reduced bone mass, while deficiency of 22 GPCRs increased bone mass and BMD; deficiency of 8 GPCRs reduced body length, while 5 mice had reduced femur size upon GPCR deletion. Furthermore, deficiency in 6 GPCRs induced osteoporosis; 4 induced osteoarthritis; 3 delayed fracture healing; 3 reduced arthritis severity; and reduced bone strength, increased bone strength, and increased cortical thickness were each observed in 2 GPCR-deficiency models. The ever-expanding number of GPCR mutation-associated diseases warrants accelerated molecular analysis, population studies, and investigation of phenotype correlation with SNPs to elucidate GPCR function in human diseases.

Analysis of porcine body size variation using re-sequencing data of miniature and large pigs

Background

Domestication has led to substantial phenotypic and genetic variation in domestic animals. In pigs, the size of so called minipigs differs by one order of magnitude compared to breeds of large body size. We used biallelic SNPs identified from re-sequencing data to compare various publicly available wild and domestic populations against two minipig breeds to gain better understanding of the genetic background of the extensive body size variation. We combined two complementary measures, expected heterozygosity and the composite likelihood ratio test implemented in “SweepFinder”, to identify signatures of selection in Minipigs. We intersected these sweep regions with a measure of differentiation, namely F_ST, to remove regions of low variation across pigs. An extraordinary large sweep between 52 and 61 Mb on chromosome X was separately analyzed based on SNP-array data of F₂ individuals from a cross of Goettingen Minipigs and large pigs.

Results

Selective sweep analysis identified putative sweep regions for growth and subsequent gene annotation provided a comprehensive set of putative candidate genes. A long swept haplotype on chromosome X, descending from the Goettingen Minipig founders was associated with a reduction of adult body length by 3% in F₂ cross-breds.

Conclusion

The resulting set of genes in putative sweep regions implies that the genetic background of body size variation in pigs is polygenic rather than mono- or oligogenic. Identified genes suggest alterations in metabolic functions and a possible insulin resistance to contribute to miniaturization. A size QTL located within the sweep on chromosome X, with an estimated effect of 3% on body length, is comparable to the largest known in pigs or other species. The androgen receptor AR, previously known to influence pig performance and carcass traits, is the most obvious potential candidate gene within this region.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-5009-y) contains supplementary material, which is available to authorized users.

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.

An SNP of the ZBTB38 gene is associated with idiopathic short stature in the Chinese Han population

OBJECTIVE

Idiopathic short stature (ISS) refers to extreme short stature without any diagnostic explanation. Recently, three genome-wide association studies discovered associations between the ZBTB38 and adult height in different populations. Therefore, variations in the ZBTB38 might contribute to ISS. Furthermore, one study in Korean population showed that ZBTB38 gene was significantly associated with adult height, but not with ISS. We want to examine whether the variants in ZBTB38 are associated with ISS in Chinese Han.

METHODS

A case-control association study was performed in 268 ISS patients and 513 healthy controls from Chinese Han population. Fourteen tag SNPs were selected and genotyped using SNaPshot method. Furthermore, expression of mRNA was quantified by RT-qPCR, and assessment of allelic expression imbalance was conducted with SNaPshot method.

RESULTS

Seven ZBTB38 SNPs were significantly associated with ISS by allele tests (rs724016, rs1582874, rs11919556, rs6440006, rs7612543, rs62282002, rs18651435). And five loci were associated with ISS according to genotype (rs11919556, rs16851419, rs6440006, rs62282002, rs18651435). Notably, after applying the stringent Bonferroni correction for multiple testing, one SNP, rs16851435, remained significantly associated by allele and genotype (P = 5·30 × 10⁻⁴ for allele and P = 0·002 for genotype). Furthermore, the rs16851435 alleles were investigated association with ZTBT38 mRNA expression levels. The G allele showed a higher transcriptional activity than the T allele (P = 0·002).

CONCLUSIONS

Our study indicated that the nonsynonymous SNP (rs16851435:T > G,p.Ser319Ala) of ZBTB38 was contributed to susceptibility of ISS in the Chinese Han population.

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.

Comparative skeletal features betweenHomo floresiensis and patients with primary growth hormone insensitivity (Laron syndrome)

Comparison between the skeletal remains of Homo floresiensis and the auxological and roentgenological findings in a large Israeli cohort of patients with Laron Syndrome (LS, primary or classical GH insensitivity or resistance) revealed striking morphological similarities, including extremely small stature and reduced cranial volume. LS is an autosomal recessive disease caused by a molecular defect of the Growth Hormone (GH) receptor or in the post-receptor cascades. Epidemiological studies have shown that LS occurs more often in consanguineous families and isolates, and it has been described in several countries in South East Asia. It is our conclusion that the findings from the island of Flores, which were attributed to a new species of the genus Homo, may in fact represent a local, highly inbred, Homo sapiens population in whom a mutation for the GH receptor had occurred.

The Role of Growth Hormone in Neural Development

Growth hormone (GH) is integrally involved in the development of the central nervous system (CNS), as well as during its recovery from injury, two processes that share many similarities and may influence CNS functionality. This review discusses some of the most recent findings in the field and, in particular, the ontogeny, distribution, regulation and putative functions of GH and its receptor within the CNS, particularly during development. The relative roles of peripheral GH, acting in part through insulin-like growth factor-I, and of the autocrine/paracrine GH system within the brain are considered. The potential role of GH as a therapeutic agent to influence brain development and function is discussed.

Differential inhibition of postnatal brain, spinal cord and body growth by a growth hormone antagonist

Background

Growth hormone (GH) plays an incompletely understood role in the development of the central nervous system (CNS). In this study, we use transgenic mice expressing a growth hormone antagonist (GHA) to explore the role of GH in regulating postnatal brain, spinal cord and body growth into adulthood. The GHA transgene encodes a protein that inhibits the binding of GH to its receptor, specifically antagonizing the trophic effects of endogenous GH.

Results

Before 50 days of postnatal age, GHA reduces spinal cord weight more than brain weight, but less than body weight. Thereafter, GHA ceases to inhibit the increase in body weight, which approaches control levels by day 150. In contrast, GHA continues to act on the CNS after day 50, reducing spinal cord growth to a greater extent and for a longer duration than brain growth.

Conclusions

Judging from its inhibition by GHA, GH differentially affects the magnitude, velocity and duration of postnatal growth of the brain, spinal cord and body. GH promotes body enlargement more than CNS growth early in postnatal life. Later, its CNS effects are most obvious in the spinal cord, which continues to exhibit GH dependence well into adulthood. As normal CNS growth slows, so does its inhibition by GHA, suggesting that reduced trophic effects of GH contribute to the postnatal slowing of CNS growth. GHA is a highly useful tool for studying the role of endogenous GH on organ-specific growth during aging.

Diagnosis and management of growth hormone deficiency in adults

In adults, GHD is a clinical syndrome that occurs in patients with pituitary or hypothalamic disease. It may be asymptomatic or present with relatively nonspecific constitutional symptoms. Most patients have abnormal body composition, consisting of increased fat mass and decreased lean mass. Life expectancy is significantly decreased in hypopituitary patients with GHD, with cardiovascular disease a common cause of death. Treatment with growth hormone reverses abnormalities in body composition and may reduce cardiovascular risk factors; however, the long-term treatment outcomes regarding mortality, the incidence of cardiovascular disease, bone fractures, tumor development, and recurrence are not known. Longer prospective clinical studies are needed. The major manufacturers of growth hormone have initiated postmarketing surveillance databases to monitor the safety of growth hormone treatment.

Genetic studies in idiopathic short stature

Idiopathic short stature (ISS) refers to a heterogeneous group of children with marked growth failure of unknown cause, and encompasses familial short stature and constitutional delay of growth. It has been postulated that specific genetic mutations may explain certain cases of growth failure. Some patients with growth hormone (GH) deficiency have mutations in the GH-releasing hormone receptor or GH gene, whereas patients with GH insensitivity syndrome have mutations in the GH receptor or insulin-like growth factor-I gene. It appears that heterozygous mutations of the GH receptor may cause partial GH insensitivity in a subset of patients with ISS. Defects in the short stature homeobox-containing gene (SHOX) in the pseudoautosomal region of the sex chromosomes may cause the growth failure seen in the Leri-Weill and Turner syndromes, and in some familial cases of ISS. Further research into stature-related genes will likely contribute to our understanding of this population.

Genetic contributions of the endothelial nitric oxide synthase gene to ovulation and menopause in a mouse model

OBJECTIVE

To investigate the influence of the endothelial nitric oxide synthase gene (Nos3) on ovulatory capacity and reproductive senescence.

DESIGN

Prospective, controlled study.

SETTING

Academic research institution.

SUBJECT(S)

Laboratory mice with targeted mutagenesis of Nos3.

INTERVENTION(S)

Hyperstimulation protocol, oocyte culture, and ovarian histology using wild-type (Nos3(+/+); n = 20), heterozygous (Nos3(+/m); n = 39), and homozygous deficient (Nos3(m/m); n = 11) female mice; observation of reproductive outcomes.

MAIN OUTCOME MEASURE(S)

Number and survival of oocytes; onset of menarche and menopause.

RESULT(S)

The mean number of superovulated oocytes (18 +/- 36 vs. 41 +/- 4) and the 48-hour overall survival rate of embryos (65% vs. 81%) were significantly reduced for Nos3(m/m) female mice compared with Nos3(+/+) female mice. Nos3(m/m) females showed a significantly reduced number and size of antral follicles and corpora lutea compared with wild-type controls. Compared with Nos3(+/m) x Nos3(+/m) breedings, Nos3(m/m) x Nos3(m/m) breedings showed a higher female age at first litter (76.2 +/- 10.3 vs. 107.8 +/- 26.6 days), fewer litters (10.5 +/- 3.6 vs. 7. 8 +/- 4.2), and a lower female age at reproductive senescence (400.2 +/- 64.5 vs. 332.1 +/- 27.4 days), respectively.

CONCLUSION(S)

Our data suggest that Nos3 deficiency is associated with reduced ovulatory capacity and impaired early embryonic viability and that it influences the onset of menarche and menopause.