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      FGFR3 gene mutation plus GRB10 gene duplication in a patient with achondroplasia plus growth delay with prenatal onset


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          Achondroplasia is a well-defined and common bone dysplasia. Genotype- and phenotype-level correlations have been found between the clinical symptoms of achondroplasia and achondroplasia-specific FGFR3 mutations.


          A 2-year-old boy with clinical features consistent with achondroplasia and Silver-Russell syndrome-like symptoms was found to carry a mutation in the fibroblast growth factor receptor-3 (FGFR3) gene at c.1138G > A (p.Gly380Arg) and a de novo 574 kb duplication at chromosome 7p12.1 that involved the entire growth-factor receptor bound protein 10 (GRB10) gene. Using quantitative real-time PCR analysis, GRB10 was over-expressed, and, using enzyme-linked immunosorbent assays for IGF1 and IGF-binding protein-3 (IGFBP3), we found that IGF1 and IGFBP3 were low-expressed in this patient.


          We demonstrate that a combination of uncommon, rare and exceptional molecular defects related to the molecular bases of particular birth defects can be analyzed and diagnosed to potentially explain the observed variability in the combination of molecular defects.

          Electronic supplementary material

          The online version of this article (doi:10.1186/s13023-016-0465-4) contains supplementary material, which is available to authorized users.

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          Disruption of the imprinted Grb10 gene leads to disproportionate overgrowth by an Igf2-independent mechanism.

          To investigate the function of the Grb10 adapter protein, we have generated mice in which the Grb10 gene was disrupted by a gene-trap insertion. Our experiments confirm that Grb10 is subject to genomic imprinting with the majority of Grb10 expression arising from the maternally inherited allele. Consistent with this, disruption of the maternal allele results in overgrowth of both the embryo and placenta such that mutant mice are at birth approximately 30% larger than normal. This observation establishes that Grb10 is a potent growth inhibitor. In humans, GRB10 is located at chromosome 7p11.2-p12 and has been associated with Silver-Russell syndrome, in which approximately 10% of those affected inherit both copies of chromosome 7 from their mother. Our results indicate that changes in GRB10 dosage could, in at least some cases, account for the severe growth retardation that is characteristic of Silver-Russell syndrome. Because Grb10 is a signaling protein capable of interacting with tyrosine kinase receptors, we tested genetically whether Grb10 might act downstream of insulin-like growth factor 2, a paternally expressed growth-promoting gene. The result indicates that Grb10 action is essentially independent of insulin-like growth factor 2, providing evidence that imprinting acts on at least two major fetal growth axes in a manner consistent with parent-offspring conflict theory.
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            Peripheral disruption of the Grb10 gene enhances insulin signaling and sensitivity in vivo.

            Grb10 is a pleckstrin homology and Src homology 2 domain-containing protein that interacts with a number of phosphorylated receptor tyrosine kinases, including the insulin receptor. In mice, Grb10 gene expression is imprinted with maternal expression in all tissues except the brain. While the interaction between Grb10 and the insulin receptor has been extensively investigated in cultured cells, whether this adaptor protein plays a positive or negative role in insulin signaling and action remains controversial. In order to investigate the in vivo role of Grb10 in insulin signaling and action in the periphery, we generated Grb10 knockout mice by the gene trap technique and analyzed mice with maternal inheritance of the knockout allele. Disruption of Grb10 gene expression in peripheral tissues had no significant effect on fasting glucose and insulin levels. On the other hand, peripheral-tissue-specific knockout of Grb10 led to significant overgrowth of the mice, consistent with a role for endogenous Grb10 as a growth suppressor. Loss of Grb10 expression in insulin target tissues, such as skeletal muscle and fat, resulted in enhanced insulin-stimulated Akt and mitogen-activated protein kinase phosphorylation. Hyperinsulinemic-euglycemic clamp studies revealed that disruption of Grb10 gene expression in peripheral tissues led to increased insulin sensitivity. Taken together, our results provide strong evidence that Grb10 is a negative regulator of insulin signaling and action in vivo.
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              Imprinting regulation of the murine Meg1/Grb10 and human GRB10 genes; roles of brain-specific promoters and mouse-specific CTCF-binding sites.

              The imprinted mouse gene Meg1/Grb10 is expres sed from maternal alleles in almost all tissues and organs, except in the brain, where it is expressed biallelically, and the paternal allele is expressed preferentially in adulthood. In contrast, the human GRB10 gene shows equal biallelic expression in almost all tissues and organs, while it is almost always expressed paternally in the fetal brain. To elucidate the molecular mechanisms of the complex imprinting patterns among the different tissues and organs of humans and mice, we analyzed in detail both the genomic structures and tissue-specific expression profiles of these species. Experiments using 5'-RACE and RT-PCR demonstrated the existence in both humans and mice of novel brain- specific promoters, in which only the paternal allele was active. The promoters were located in the primary differentially methylated regions. Interest ingly, CTCF-binding sites were found only in the mouse promoter region where CTCF showed DNA methylation-sensitive binding activity. Thus, the insulator function of CTCF might cause reciprocal maternal expression of the Meg1/Grb10 gene from another upstream promoter in the mouse, whereas the human upstream promoter is active in both parental alleles due to the lack of the corresponding insulator sequence in this region.

                Author and article information

                Orphanet J Rare Dis
                Orphanet J Rare Dis
                Orphanet Journal of Rare Diseases
                BioMed Central (London )
                2 July 2016
                2 July 2016
                : 11
                : 89
                [ ]Guangzhou KingMed Center for Clinical Laboratory Co., Ltd, Guangzhou, 510330 Guangdong China
                [ ]KingMed School of Laboratory Medicine, Guangzhou Medical University, Guangzhou, 510330 Guangdong China
                [ ]Fetal Medicine Centre, Department of Obstetrics and Gynaecology, The First Affiliated Hospital of Sun Yat Sen University, Guangzhou, Guangdong 510080 China
                [ ]Fairmont Preparatory Academy, Anaheim, CA 92801 USA
                [ ]Affymetrix Biotech Shanghai Ltd., Shanghai, 200020 China
                [ ]Key Laboratory for Major Obstetric Diseases of Guangdong Province, Key Laboratory of Reproduction and Genetics of Guangdong Higher Education Institutes, The Third Affiliated Hospital of Guangzhou Medical University, 63 Duobao Rd., Guangzhou, 510150 People’s Republic of China
                Author information
                © The Author(s). 2016

                Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License ( http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver ( http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.

                : 29 March 2016
                : 9 June 2016
                Funded by: the National Natural Science Foundation Committee of China
                Award ID: NSFC-81500974
                Award Recipient :
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                © The Author(s) 2016

                Infectious disease & Microbiology
                achondroplasia,grb10,duplication,over-expression,silver-russell syndrome


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