IGF2 Mutations

Pathogenic sequence variant and microdeletion affecting HMGA2 in Silver-Russell syndrome: case reports and literature review

Silver-Russell syndrome (SRS) is a representative imprinting disorder characterized by pre- and postnatal growth failure. We encountered two Japanese SRS cases with a de novo pathogenic frameshift variant of HMGA2 (NM_003483.6:c.138_141delinsCT, p.(Lys46Asnfs*16)) and a de novo ~ 3.4 Mb microdeletion at 12q14.2-q15 involving HMGA2, respectively. Furthermore, we compared clinical features in previously reported patients with various genetic conditions leading to compromised IGF2 expression, i.e., HMGA2 aberrations, PLAG1 aberrations, IGF2 aberrations, and H19/IGF2:IG-DMR epimutations (hypomethylations). The results provide further support for HMGA2 being involved in the development of SRS and imply some characteristic features in patients with HMGA2 aberrations.

Case report: Long term response to growth hormone in a child with Silver-Russell syndrome-like phenotype due to a novel paternally inherited IGF2 variant

Silver-Russell syndrome (SRS, OMIM, 180860) is a rare genetic disorder with a wide spectrum of symptoms. The most common features are intrauterine growth retardation (IUGR), poor postnatal development, macrocephaly, triangular face, prominent forehead, body asymmetry, and feeding problems. The diagnosis of SRS is based on a combination of clinical features. Up to 60% of SRS patients have chromosome 7 or 11 abnormalities, and <1% show abnormalities in IGF2 signaling pathway genes (IGF2, HMGA2, PLAG1 and CDKN1C). The underlying genetic cause remains unknown in about 40% of cases (idiopathic SRS). We report a novel IGF2 variant c.[-6-2A>G] (NM_000612) in a child with severe IUGR and clinical features of SRS and confirm the utility of targeted exome sequencing in patients with negative results to common genetic analyses. In addition, we report that long-term growth hormone treatment improves height SDS in this patient.

Dysfunction in IGF2R Pathway and Associated Perturbations in Autophagy and WNT Processes in Beckwith-Wiedemann Syndrome Cell Lines

Beckwith-Wiedemann Syndrome (BWS) is an imprinting disorder characterized by overgrowth, stemming from various genetic and epigenetic changes. This study delves into the role of IGF2 upregulation in BWS, focusing on insulin-like growth factor pathways, which are poorly known in this syndrome. We examined the IGF2R, the primary receptor of IGF2, WNT, and autophagy/lysosomal pathways in BWS patient-derived lymphoblastoid cell lines, showing different genetic and epigenetic defects. The findings reveal a decreased expression and mislocalization of IGF2R protein, suggesting receptor dysfunction. Additionally, our results point to a dysregulation in the AKT/GSK-3/mTOR pathway, along with imbalances in autophagy and the WNT pathway. In conclusion, BWS cells, regardless of the genetic/epigenetic profiles, are characterized by alteration of the IGF2R pathway that is associated with the perturbation of the autophagy and lysosome processes. These alterations seem to be a key point of the molecular pathogenesis of BWS and potentially contribute to BWS's characteristic overgrowth and cancer susceptibility. Our study also uncovers alterations in the WNT pathway across all BWS cell lines, consistent with its role in growth regulation and cancer development.

Human Reproduction and Disturbed Genomic Imprinting

Genomic imprinting is a specific mode of gene regulation which particularly accounts for the factors involved in development. Its disturbance affects the fetus, the course of pregnancy and even the health of the mother. In children, aberrant imprinting signatures are associated with imprinting disorders (ImpDis). These alterations also affect the function of the placenta, which has consequences for the course of the pregnancy. The molecular causes of ImpDis comprise changes at the DNA level and methylation disturbances (imprinting defects/ImpDefs), and there is an increasing number of reports of both pathogenic fetal and maternal DNA variants causing ImpDefs. These ImpDefs can be inherited, but prediction of the pregnancy complications caused is difficult, as they can cause miscarriages, aneuploidies, health issues for the mother and ImpDis in the child. Due to the complexity of imprinting regulation, each pregnancy or patient with suspected altered genomic imprinting requires a specific workup to identify the precise molecular cause and also careful clinical documentation. This review will cover the current knowledge on the molecular causes of aberrant imprinting signatures and illustrate the need to identify this basis as the prerequisite for personalized genetic and reproductive counselling of families.

Hormonal Determinants of Growth and Weight Gain in the Human Fetus and Preterm Infant

The factors controlling linear growth and weight gain in the human fetus and newborn infant are poorly understood. We review here the changes in linear growth, weight gain, lean body mass, and fat mass during mid- and late gestation and the early postnatal period in the context of changes in the secretion and action of maternal, placental, fetal, and neonatal hormones, growth factors, and adipocytokines. We assess the effects of hormonal determinants on placental nutrient delivery and the impact of preterm delivery on hormone expression and postnatal growth and metabolic function. We then discuss the effects of various maternal disorders and nutritional and pharmacologic interventions on fetal and perinatal hormone and growth factor production, growth, and fat deposition and consider important unresolved questions in the field.

Familial Pseudohypoparathyroidism Type IB Associated with an SVA Retrotransposon Insertion in the GNAS Locus

Loss of methylation (LOM) at GNAS-A/B:TSS-differentially methylated regions (DMRs) in the GNAS locus is observed in pseudohypoparathyroidism type 1B (PHP1B). Many PHP1B cases are sporadic, but autosomal dominant-PHP1B has a deletion involving NESP55 expressed from the maternal allele or STX16 located upstream of the GNAS locus on the maternal allele. We report the possible first familial PHP1B cases with retrotransposon insertion in the GNAS locus on the maternal allele. To our knowledge, they are the possible first cases with imprinting disorders caused by retrotransposon insertion. The two sibling cases experienced tetany and/or cramps from school age and had hypocalcemia and an increased serum intact parathyroid hormone (PTH) level together with overweight, round face, and normal intellectual levels. Methylation analysis for DMRs in the GNAS locus showed only LOM of the GNAS-A/B:TSS-DMR. Copy number abnormalities at STX16 and the GNAS locus were not detected by array comparative genomic hybridization. Whole-genome sequencing and Sanger sequencing revealed an approximately 1000-bp SVA retrotransposon insertion upstream of the first exon of A/B on the GNAS locus in these siblings. Whole-genome methylome analysis by Enzymatic Methyl-Seq in the siblings showed normal methylation status in the region surrounding the insertion site and mild LOM of the GNAS-A/B:TSS-DMR. We conducted transcriptome analysis using mRNA from skin fibroblasts and induced pluripotent stem cells (iPSCs) derived from the siblings and detected no aberrant NESP55 transcripts. Quantitative reverse-transcriptase PCR (qRT-PCR) analysis in skin fibroblasts showed increased A/B expression in the patients and no NESP55 expression, even in a control. qRT-PCR analysis in iPSCs showed decreased NESP55 expression with normal methylation status of the GNAS-NESP:TSS-DMR in the patients. The retrotransposon insertion in the siblings likely caused decreased NESP55 expression that could lead to increased A/B expression via LOM of the GNAS-A/B:TSS-DMR, subsequent reduced Gsα expression, and finally, PHP1B development. © 2022 American Society for Bone and Mineral Research (ASBMR).

IGF2: Development, Genetic and Epigenetic Abnormalities

In the 30 years since the first report of parental imprinting in insulin-like growth factor 2 (Igf2) knockout mouse models, we have learnt much about the structure of this protein, its role and regulation. Indeed, many animal and human studies involving innovative techniques have shed light on the complex regulation of IGF2 expression. The physiological roles of IGF-II have also been documented, revealing pleiotropic tissue-specific and developmental-stage-dependent action. Furthermore, in recent years, animal studies have highlighted important interspecies differences in IGF-II function, gene expression and regulation. The identification of human disorders due to impaired IGF2 gene expression has also helped to elucidate the major role of IGF-II in growth and in tumor proliferation. The Silver-Russell and Beckwith-Wiedemann syndromes are the most representative imprinted disorders, as they constitute both phenotypic and molecular mirrors of IGF2-linked abnormalities. The characterization of patients with either epigenetic or genetic defects altering IGF2 expression has confirmed the central role of IGF-II in human growth regulation, particularly before birth, and its effects on broader body functions, such as metabolism or tumor susceptibility. Given the long-term health impact of these rare disorders, it is important to understand the consequences of IGF2 defects in these patients.

ALX1-transcribed LncRNA AC132217.4 promotes osteogenesis and bone healing via IGF-AKT signaling in mesenchymal stem cells

The osteogenic potential of bone marrow mesenchymal stem cells (BMSCs) is critical for bone formation and regeneration. A high non-/delayed-union rate of fracture healing still occurs in specific populations, implying an urgent need to discover novel targets for promoting osteogenesis and bone regeneration. Long non-coding (lnc)RNAs are emerging regulators of multiple physiological processes, including osteogenesis. Based on differential expression analysis of RNA sequencing data, we found that lncRNA AC132217.4, a 3'UTR-overlapping lncRNA of insulin growth factor 2 (IGF2), was highly induced during osteogenic differentiation of BMSCs. Afterward, both gain-of-function and loss-of-function experiments proved that AC132217.4 promotes osteoblast development from BMSCs. As for its molecular mechanism, we found that AC132217.4 binds with IGF2 mRNA to regulate its expression and downstream AKT activation to control osteoblast maturation and function. Furthermore, we identified two splicing factors, splicing component 35 KDa (SC35) and heterogeneous nuclear ribonucleoprotein A1 (HNRNPA1), which regulate the biogenesis of AC132217.4 at the post-transcriptional level. We also identified a transcription factor, ALX1, which regulates AC132217.7 expression at the transcriptional level to promote osteogenesis. Importantly, in-vivo over-expression of AC132217.4 essentially promotes the bone healing process in a murine tibial drill-hole model. Our study demonstrates that lncRNA AC132217.4 is a novel anabolic regulator of BMSC osteogenesis and could be a plausible therapeutic target for improving bone regeneration.

Frequency and clinical characteristics of distinct etiologies in patients with Silver-Russell syndrome diagnosed based on the Netchine-Harbison clinical scoring system

Silver-Russel syndrome (SRS) is a representative imprinting disorder (ID) characterized by growth failure and diagnosed by clinical features. Recently, international consensus has recommended using the Netchine-Harbison clinical scoring system (NH-CSS) as clinical diagnostic criteria. Loss of methylation of H19/IGF2:intergenic differentially methylated region (H19LOM) and maternal uniparental disomy chromosome 7 (UPD(7)mat) are common etiologies of SRS; however, other IDs, pathogenic variants (PVs) of genes, and pathogenic copy number variants (PCNVs) have been reported in patients meeting NH-CSS. To clarify the frequency and clinical characteristics of each etiology, we conducted (epi)genetic analysis in 173 patients satisfying NH-CSS. H19LOM and UPD(7)mat were identified in 34.1%. PCNVs, other IDs, and PVs were in 15.0%. Patients with all six NH-CSS items were most frequently observed with H19LOM and UPD(7)mat. This study confirmed the suitability of NH-CSS as clinical diagnostic criteria, the (epi)genetic heterogeneity of SRS, and showed the necessity of further discussion regarding the "SRS spectrum".

Microdeletions in 1q21 and 8q12.1 depict two additional molecular subgroups of Silver-Russell syndrome like phenotypes

Background

Silver-Russell syndrome (SRS) is a genetic disorder characterized by intrauterine and postnatal growth restriction, relative macrocephaly at birth, body asymmetry and typical facial features. Clinical and molecular heterogeneity is described in SRS. Common causes are loss of methylation of the imprinting center 1 in 11p15 and maternal uniparental disomy of chromosome 7. Other genetic alterations include disturbances of imprinted regions in 14q32, 7q32 and 11p15 as well as submicroscopic deletions and duplications. Single nucleotide variants in genes like IGF2, HMGA2, PLAG1, CDKN1C have also been identified in patients with SRS phenotypes. However, routine molecular diagnostics usually focus on 11p15 and chromosome 7, while less frequent causes are not systematically addressed.

Results

Here we report two patients with SRS features in which molecular karyotyping revealed microdeletions in 1q21 and 8q12.1 respectively. In a 3.5-year-old girl with postnatal growth restriction, feeding difficulties, relative macrocephaly and distinct SRS features a 2 Mb deletion in 1q21.1q21.2 was identified. Our second case is a 1.5-year-old boy with intrauterine and postnatal growth restriction, feeding difficulties and distinct facial features with a 77 kb deletion in 8q12.1 affecting PLAG1 as the only protein-encoding gene with known function.

Conclusions

The 1q21 region has not yet been assigned as an SRS region, although six patients with the same deletion and SRS features including relative macrocephaly have been described before. This new case adds to the evidence that distal 1q21 should be annotated as an SRS candidate region. The PLAGL1 alteration is the smallest deletion in 8q12.1 ever reported in a patient with SRS phenotype and it finally confirms that PLAG1 is the SRS causing gene in 8q12.1. To increase the diagnostic yield in patients with suspected SRS, we recommend both molecular karyotyping and next generation sequencing-based approaches.

The Mechanism of Insulin-Like Growth Factor II mRNA-Binging Protein 3 Induce Decidualization and Maternal-Fetal Interface Cross Talk by TGF-β1 in Recurrent Spontaneous Abortion

Recurrent spontaneous abortion (RSA) is defined as the loss of two or more consecutive intrauterine pregnancies that are clinically established early in pregnancy. To date, the etiology and underlying mechanisms of RSA remain unclear. It is widely thought that the impairment of decidualization is inclined to induce subsequent pregnancy failure and leads to the dysregulation of extra-villous trophoblast invasion and proliferation through maternal–fetal cross talk. However, the mechanism of decidualization in RSA has yet to be understood. In our study, we demonstrate that decidual samples from RSA patients have significantly higher insulin-like growth factor 2 mRNA-binding protein 3 (IGF2BP3) and lower TGF-β1 levels compared to healthy controls. In addition, the overexpression of IGF2BP3 in human endometrial stromal cells (hESCs) can lead to the impairment of decidualization in vitro-induced model and the abnormal cell cycle regulation. Furthermore, TGF-β1 and MMP9 levels were greatly increased after decidualization, whereas IGF2BP3 overexpression inhibited endometrial mesenchymal decidualization by downregulating TGF-β1, impeding maternal–fetal interface cytokine cross talk, and limiting the ability of trophoblast invasion. In conclusion, our investigation first demonstrates that abnormal elevation of IGF2BP3 in the pregnant endometrium leads to the impairment of decidualization and abnormal trophoblast invasion, thereby predisposing individuals to RSA.

Case report: A novel de novo IGF2 missense variant in a Finnish patient with Silver-Russell syndrome

Silver-Russell syndrome (SRS, OMIM 180860) is a rare imprinting disorder characterized by intrauterine and postnatal growth restriction, feeding difficulties in early childhood, characteristic facial features, and body asymmetry. The molecular cause most commonly relates to hypomethylation of the imprinted 11p15.5 IGF2/H19 domain but remains unknown in about 40% of the patients. Recently, heterozygous paternally inherited pathogenic variants in IGF2, the gene encoding insulin-like growth factor 2 (IGF2), have been identified in patients with SRS. We report a novel de novo missense variant in IGF2 (c.122T > G, p.Leu41Arg) on the paternally derived allele in a 16-year-old boy with a clinical diagnosis of SRS. The missense variant was identified by targeted exome sequencing and predicted pathogenic by multiple in silico tools. It affects a highly conserved residue on a domain that is important for binding of other molecules. Our finding expands the spectrum of disease-causing variants in IGF2. Targeted exome sequencing is a useful diagnostic tool in patients with negative results of common diagnostic tests for SRS.

High glucose increases IGF-2/H19 expression by changing DNA methylation in HTR8/SVneo trophoblast cells

INTRODUCTION

Gestational diabetes mellitus (GDM) is associated with many adverse outcomes of pregnancy, especially macrosomia. The aim of our study was to verify whether high glucose concentrations change the methylation levels of the insulin-like growth factor-2 (IGF-2)/H19 gene promoters to increase the expression of IGF-2, a key gene in fetal growth regulation.

METHODS

HTR8/SVneo cells were used to establish a cell model of intrauterine hyperglycemia in pregnant women with GDM. The RNA expression levels of the IGF-2/H19 genes and the methylation levels of the IGF-2/H19 gene promoter regions were measured. Methylated and unmethylated IGF-2/H19 gene promoter plasmids were transfected into HTR8/SVneo cells.

RESULTS

Among the five groups of cells, the RNA levels of IGF-2 and H19 were lowest in the 5-mM (physiological blood glucose level) group, which was statistically significant (all P < 0.05). Compared with those in the 5-mM group, two cytosine-phosphate-guanine (CpG) sites in the promoter region of the IGF-2 gene and twelve CpG sites in the promoter region of the H19 gene had statistically significant changes in methylation levels (all P < 0.05). Additionally, luciferase activity was significantly higher in cells transfected with the methylated H19 gene promoter plasmid than in control cells transfected with the unmethylated plasmid (P < 0.01), while the methylated IGF-2 gene promoter plasmid produced lower luciferase activity than the unmethylated plasmid (P < 0.01).

DISCUSSION

High glucose concentrations may increase IGF-2/H19 expression by changing the methylation levels of the IGF-2 and H19 gene promoters.

Insulin-Like Growth Factor-II and Ischemic Stroke-A Prospective Observational Study

Insulin-like growth factor-II (IGF-II) regulates prenatal brain development, but the role in adult brain function and injury is unclear. Here, we determined whether serum levels of IGF-II (s-IGF-II) are associated with mortality and functional outcome after ischemic stroke (IS). The study population comprised ischemic stroke cases (n = 492) and controls (n = 514) from the Sahlgrenska Academy Study on Ischemic Stroke (SAHLSIS). Functional outcome was evaluated after 3 months and 2 years using the modified Rankin Scale (mRS), and additionally, survival was followed at a minimum of 7 years or until death. S-IGF-II levels were higher in IS cases both in the acute phase and at 3-month follow-up compared to controls (p < 0.05 and p < 0.01, respectively). The lowest quintile of acute s-IGF-II was, compared to the four higher quintiles, associated with an increased risk of post-stroke mortality (median follow-up 10.6 years, crude hazard ratio (HR) 2.34, 95% confidence interval (CI) 1.56–3.49, and fully adjusted HR 1.64, 95% CI 1.02–2.61). In contrast, crude associations with poor functional outcome (mRS 3–6) lost significance after full adjustment for covariates. In conclusion, s-IGF-II was higher in IS cases than in controls, and low acute s-IGF-II was an independent risk marker of increased mortality.

Growth Restriction and Genomic Imprinting-Overlapping Phenotypes Support the Concept of an Imprinting Network

Intrauterine and postnatal growth disturbances are major clinical features of imprinting disorders, a molecularly defined group of congenital syndromes caused by molecular alterations affecting parentally imprinted genes. These genes are expressed monoallelically and in a parent-of-origin manner, and they have an impact on human growth and development. In fact, several genes with an exclusive expression from the paternal allele have been shown to promote foetal growth, whereas maternally expressed genes suppress it. The evolution of this correlation might be explained by the different interests of the maternal and paternal genomes, aiming for the conservation of maternal resources for multiple offspring versus extracting maximal maternal resources. Since not all imprinted genes in higher mammals show the same imprinting pattern in different species, the findings from animal models are not always transferable to human. Therefore, human imprinting disorders might serve as models to understand the complex regulation and interaction of imprinted loci. This knowledge is a prerequisite for the development of precise diagnostic tools and therapeutic strategies for patients affected by imprinting disorders. In this review we will specifically overview the current knowledge on imprinting disorders associated with growth retardation, and its increasing relevance in a personalised medicine direction and the need for a multidisciplinary therapeutic approach.

Genetic causes of growth hormone insensitivity beyond GHR

Growth hormone insensitivity (GHI) syndrome, first described in 1966, is classically associated with monogenic defects in the GH receptor (GHR) gene which result in severe post-natal growth failure as consequences of insulin-like growth factor I (IGF-I) deficiency. Over the years, recognition of other monogenic defects downstream of GHR has greatly expanded understanding of primary causes of GHI and growth retardation, with either IGF-I deficiency or IGF-I insensitivity as clinical outcomes. Mutations in IGF1 and signaling component STAT5B disrupt IGF-I production, while defects in IGFALS and PAPPA2, disrupt transport and release of circulating IGF-I, respectively, affecting bioavailability of the growth-promoting IGF-I. Defects in IGF1R, cognate cell-surface receptor for IGF-I, disrupt not only IGF-I actions, but actions of the related IGF-II peptides. The importance of IGF-II for normal developmental growth is emphasized with recent identification of defects in the maternally imprinted IGF2 gene. Current application of next-generation genomic sequencing has expedited the pace of identifying new molecular defects in known genes or in new genes, thereby expanding the spectrum of GH and IGF insensitivity. This review discusses insights gained and future directions from patient-based molecular and functional studies.

Unusual deletion of the maternal 11p15 allele in Beckwith-Wiedemann syndrome with an impact on both imprinting domains

Background

Whereas duplications in 11p15.5 covering both imprinting centers (ICs) and their subordinated genes account for up to 1% of Beckwith–Wiedemann and Silver–Russell syndrome patients (BWS, SRS), the deletions in 11p15.5 reported so far only affect one of the ICs. In these cases, not only the size and gene content had an impact on the phenotype, but also the sex of the contributing parent influences the clinical signs of the deletion carrier.

Results

We here report on the first case with a heterozygous deletion within the maternal allele affecting genes which are regulated by both ICs in 11p15.5 in a BWS patient, and describe the molecular and clinical consequences in case of its maternal or paternal inheritance.

Conclusions

The identification of a unique deletion affecting both 11p15.5 imprinting domains in a BWS patient illustrates the complexity of the regulation mechanisms in these key imprinting regions.

One test for all: whole exome sequencing significantly improves the diagnostic yield in growth retarded patients referred for molecular testing for Silver-Russell syndrome

Background

Silver-Russell syndrome (SRS) is an imprinting disorder which is characterised by severe primordial growth retardation, relative macrocephaly and a typical facial gestalt. The clinical heterogeneity of SRS is reflected by a broad spectrum of molecular changes with hypomethylation in 11p15 and maternal uniparental disomy of chromosome 7 (upd(7)mat) as the most frequent findings. Monogenetic causes are rare, but a clinical overlap with numerous other disorders has been reported. However, a comprehensive overview on the contribution of mutations in differential diagnostic genes to phenotypes reminiscent to SRS is missing due to the lack of appropriate tests. With the implementation of next generation sequencing (NGS) tools this limitation can now be circumvented.

Main body

We analysed 75 patients referred for molecular testing for SRS by a NGS-based multigene panel, whole exome sequencing (WES), and trio-based WES. In 21/75 patients a disease-causing variant could be identified among them variants in known SRS genes (IGF2, PLAG1, HMGA2). Several patients carried variants in genes which have not yet been considered as differential diagnoses of SRS.

Conclusions

WES approaches significantly increase the diagnostic yield in patients referred for SRS testing. Several of the identified monogenetic disorders have a major impact on clinical management and genetic counseling.

Novel Variant in PLAG1 in a Familial Case with Silver-Russell Syndrome Suspicion

Silver-Russell syndrome (SRS) is a rare growth-related genetic disorder that is mainly associated with prenatal and postnatal growth retardation. Molecular causes are not clear in all cases, the most common ones being loss of methylation on chromosome 11p15 (≈50%) and maternal uniparental disomy for chromosome 7 (upd(7)mat) (≈10%). However, pathogenic variants in genes such as CDKN1C, HMGA2, IGF2, or PLAG1 have also been described. Previously, two families and one sporadic case have been reported with PLAG1 alterations. Here, we present a case of a female with clinical suspicion of SRS (i.e., intrauterine and postnatal growth retardation, triangular face, psychomotor delay, speech delay, feeding difficulties). No alterations in methylation or copy number were detected at chromosomes 11p15 and 7 using methylation-specific multiplex ligation-dependent probe amplification (MS-MLPA). The custom panel study by next-generation sequencing (NGS) revealed a frameshift variant in the PLAG1 gene (NM_002655.3:c.551delA; p.(Lys184Serfs *45)). Familial studies confirmed that the variant was inherited from the mother and it was also present in other family members. New evidence of pathogenic alterations in the HMGA2-PLAG1-IGF2 pathway suggest the importance of studying and taking into account these genes as alternative molecular causes of Silver-Russell syndrome.

Novel mutation points to a hot spot in CDKN1C causing Silver-Russell syndrome

BACKGROUND

Pathogenic CDKN1C gain-of-function variants on the maternal allele were initially reported as a cause of IMAGe syndrome characterized by intrauterine growth retardation, metaphyseal dysplasia, primary adrenal insufficiency and genital anomalies. Recently, a maternally inherited CDKN1C missense mutation (p.Arg279Leu) was identified in several members of a single family clinically diagnosed with Silver-Russell syndrome (SRS) but without adrenal insufficiency. Thereafter, two half siblings from UK with familial SRS were described who carried the same mutation. This specific amino acid change is located within a narrow functional region containing the mutations previously associated with IMAGe syndrome.

RESULTS

Here, we describe a third familial case with maternally inherited SRS due to a missense variant affecting the same amino acid position 279 but leading to a different amino acid substitution (p. (Arg279Ser)). The two affected family members (mother and son) presented with the complete SRS phenotype (both Netchine-Harbison CSS score 5 of 6) but without body asymmetry or adrenal insufficiency.

CONCLUSIONS

In comparison with loss-of-function genomic IGF2 mutations, CDKN1C gain-of-function mutations are a less frequent cause of SRS and seem to affect a cluster of few amino acids.

Contribution of gene mutations to Silver-Russell syndrome phenotype: multigene sequencing analysis in 92 etiology-unknown patients

BACKGROUND

Silver-Russell syndrome (SRS) is characterized by growth failure and dysmorphic features. Major (epi)genetic causes of SRS are loss of methylation on chromosome 11p15 (11p15 LOM) and maternal uniparental disomy of chromosome 7 (upd(7)mat). However, IGF2, CDKN1C, HMGA2, and PLAG1 mutations infrequently cause SRS. In addition, other imprinting disturbances, pathogenic copy number variations (PCNVs), and monogenic disorders sometimes lead to SRS phenotype. This study aimed to clarify the frequency and clinical features of the patients with gene mutations among etiology-unknown patients with SRS phenotype.

RESULTS

Multigene sequencing was performed in 92 out of 336 patients referred to us for genetic testing for SRS. The clinical features of the patients were evaluated based on the Netchine-Harbison clinical scoring system. None of the patients showed 11p15 LOM, upd(7)mat, abnormal methylation levels for six differentially methylated regions (DMRs), namely, PLAGL1:alt-TSS-DMR on chromosome 6, KCNQ1OT1:TSS-DMR on chromosome 11, MEG3/DLK1:IG-DMR on chromosome 14, MEG3:TSS-DMR on chromosome 14, SNURF:TSS-DMR on chromosome 15, and GNAS A/B:TSS-DMR on chromosome 20, PCNVs, or maternal uniparental disomy of chromosome 16. Using next-generation sequencing and Sanger sequencing, we screened four SRS-causative genes and 406 genes related to growth failure and/or skeletal dysplasia. We identified four pathogenic or likely pathogenic variants in responsible genes for SRS (4.3%: IGF2 in two patients, CDKN1C, and PLAG1), and five pathogenic variants in causative genes for known genetic syndromes presenting with growth failure (5.4%: IGF1R abnormality (IGF1R), SHORT syndrome (PIK3R1), Floating-Harbor syndrome (SRCAP), Pitt-Hopkins syndrome (TCF4), and Noonan syndrome (PTPN11)). Functional analysis indicated the pathogenicity of the CDKN1C variant. The variants we detected in CDKN1C and PLAG1 were the second and third variants leading to SRS, respectively. Our patients with CDKN1C and PLAG1 variants showed similar phenotypes to previously reported patients. Furthermore, our data confirmed IGF1R abnormality, SHORT syndrome, and Floating-Harbor syndrome are differential diagnoses of SRS because of the shared phenotypes among these syndromes and SRS. On the other hand, the patients with pathogenic variants in causative genes for Pitt-Hopkins syndrome and Noonan syndrome were atypical of these syndromes and showed partial clinical features of SRS.

CONCLUSIONS

We identified nine patients (9.8%) with pathogenic or likely pathogenic variants out of 92 etiology-unknown patients with SRS phenotype. This study expands the molecular spectrum of SRS phenotype.