Carrying both COL1A2 and FBN2 gene heterozygous mutations results in a severe skeletal clinical phenotype: an affected family.

BACKGROUND: Osteogenesis imperfecta (OI) is the most common monogenic disease of the skeletal system and is usually caused by mutations in the COL1A1 or COL1A2 genes. Congenital contractural arachnodactyly syndrome (CCA) is an autosomal dominant hereditary disease of connective tissue. To date, the FBN2 gene is the only gene reported to cause CCA. Researchers found that COL1A2 and FBN2 are both involved in the extracellular matrix organization pathway. These findings suggest that these two genes play an important role in a similar mechanism and may trigger a synergistic effect. METHODS: Trio-whole-exome sequencing (Trio-WES) was performed to analyse the underlying genetic cause of a proband with OI in a Chinese family. Sanger sequencing was used to validate the mutations in 3 members of the family with OI with varying degrees of severity of skeletal abnormalities and the members with no clinical signs. RESULT: A c.3304G > C mutation in the COL1A2 gene (p.Gly1102Arg) and a novel c.4108G > T mutation in the FBN2 gene (p.Glu1370*) were detected in the proband, an affected member of the family. The affected individuals with both mutations present a more severe phenotype, while affected individuals present a milder phenotype if only the mutation in COL1A2 is detected (c.3304G > C). The unaffected individual in this family did not have any mutations in the COL1A2 gene or FBN2 gene. CONCLUSION: Our study is the first clinical report to indicate that patients carrying concomitant mutations in both the COL1A2 and FBN2 genes may present with more severe skeletal abnormalities. Furthermore, our study suggests the possibility of synergistic effects between the COL1A2 and FBN2 genes.

[Analysis of phenotype and genetic variant in a family with Shprintzen-Goldberg syndrome].

OBJECTIVE: To explore the genetic basis for a proband with Shprintzen-Goldberg syndrome (SGS). METHODS: Whole exome sequencing was carried out to detect potential variants associated with the relevant phenotypes. Candidate variants were verified by Sanger sequencing of the patient and her family. RESULTS: DNA sequencing revealed that that the proband has carried a de novo heterozygous missense c.94C>G (p.Leu32Val) variant in exon 1 of the SKI gene (NM_003036), which has been reported previously. The same variant was not detected in either parent. Based on the guidelines of the American College of Medical Genetics and Genomics, the variant was predicted to be pathogenic (PS1+PS2+PM1+PM2+PP2+PP3). CONCLUSION: The SKI c.94C>G (p. Leu32Val) variant probably underlay the autosomal dominant SGS in this patient.

[A novel splicing acceptor variant of the FBN2 gene contributes to a case of congenital contractural arachnodactyly].

OBJECTIVE: To identify the pathogenic variants from a patient with suspected congenital contractural arachnodactyly, and to explore the possible molecular genetic pathogenesis, so as to provide evidence for clinical diagnosis. METHODS: Whole exome sequencing was performed for the patient. The splicing site variation of candidate pathogenic genes was verified by Sanger sequencing, and the new transcript sequence was determined by RT-PCR and TA-cloning sequencing. RESULTS: The patient carried a heterozygous c.533-1G>C variant of FBN2 gene, which was not reported. The sequencing of mRNA showed that the variant leaded to the disappearance of the canonical splice acceptor site of FBN2 gene and the activation of a cryptic splice acceptor site at c.533-71, resulting in the insertion of 70 bp sequence in the new transcript. It was speculated that the polypeptide encoded by the new transcript changed from valine (Val) to serine (Ser) at amino acid 179, and prematurely terminated after 26 aminoacids. According to the guidelines of American College of Medical Genetics and Genomics, the variant of FBN2 gene c. 533-1G>C was determined as pathogenic (PVS1+PM2+PP3 ). CONCLUSION: A novel splicing variant of FBN2 gene (c.533-1G>C) was identified, which can lead to congenital contractural arachnodactyly.

Two novel variants in SCARF2 gene underlie van den Ende-Gupta syndrome.

Van den Ende-Gupta syndrome (VDEGS) (MIM#600920) is characterized by skeletal and craniofacial abnormalities that include prominent ears, downslanting palpebral fissures, blepharophimosis, hypoplastic maxilla with or without a cleft palate, a narrow and convex nasal bridge and an everted lower lip, camptodactyly and arachnodactyly. Intelligence is normal. Recent studies have reported that patients with VDEGS have pathogenic variants in the SCARF2 gene on chromosome 22q11.21. Here, we report two Turkish patients with two novel variants [c.2291_2292insC (p.Ser765LeufsTer6) and c.488G>A (p.Cys63Tyr)] in the SCARF2 gene. In silico analysis predicted that both of these novel variants were pathogenic. To the best of our knowledge, this is the first case report of this syndrome in Turkey.

Loeys-Dietz and Shprintzen-Goldberg syndromes: analysis of TGF-ß-opathies with craniofacial manifestations using an innovative multimodality method.

BACKGROUND: Elevated transforming growth factor-beta (TGF-ß) signalling has been implicated in the pathogenesis of Loeys-Dietz syndrome (LDS) and Shprintzen-Goldberg syndrome (SGS). In this study, we provide a qualitative and quantitative analysis of the craniofacial and functional features among the LDS subtypes and SGS. METHODS: We explore the variability within and across a cohort of 44 patients through deep clinical phenotyping, three-dimensional (3D) facial photo surface analysis, cephalometric and geometric morphometric analyses of cone-beam CT scans. RESULTS: The most common craniofacial features detected in this cohort include mandibular retrognathism (84%), flat midface projection (84%), abnormal eye shape (73%), low-set ears (73%), abnormal nose (66%) and lip shape (64%), hypertelorism (41%) and a relatively high prevalence of nystagmus/strabismus (43%), temporomandibular joint disorders (38%) and obstructive sleep apnoea (23%). 3D cephalometric analysis demonstrated an increased cranial base angle with shortened anterior cranial base and underdevelopment of the maxilla and mandible, with evidence of a reduced pharyngeal airway in 55% of those analysed. Geometric morphometric analysis confirmed that the greatest craniofacial shape variation was among patients with LDS type 2, with distinct clustering of patients with SGS. CONCLUSIONS: This comprehensive phenotypic approach identifies developmental abnormalities that segregate to mutation variants along the TGF-ß signalling pathway, with a particularly severe phenotype associated with TGFBR2 and SKI mutations. Multimodality assessment of craniofacial anomalies objectively reveals the impact of mutations of the TGF-ß pathway with perturbations associated with the cranium and cranial base with severe downstream effects on the orbit, maxilla and mandible with the resultant clinical phenotypes.

A novel splicing acceptor variant of the FBN2 gene contributes to a case of congenital contractural arachnodactyly / 中华医学遗传学杂志

OBJECTIVE@#To identify the pathogenic variants from a patient with suspected congenital contractural arachnodactyly, and to explore the possible molecular genetic pathogenesis, so as to provide evidence for clinical diagnosis.@*METHODS@#Whole exome sequencing was performed for the patient. The splicing site variation of candidate pathogenic genes was verified by Sanger sequencing, and the new transcript sequence was determined by RT-PCR and TA-cloning sequencing.@*RESULTS@#The patient carried a heterozygous c.533-1G>C variant of FBN2 gene, which was not reported. The sequencing of mRNA showed that the variant leaded to the disappearance of the canonical splice acceptor site of FBN2 gene and the activation of a cryptic splice acceptor site at c.533-71, resulting in the insertion of 70 bp sequence in the new transcript. It was speculated that the polypeptide encoded by the new transcript changed from valine (Val) to serine (Ser) at amino acid 179, and prematurely terminated after 26 aminoacids. According to the guidelines of American College of Medical Genetics and Genomics, the variant of FBN2 gene c. 533-1G>C was determined as pathogenic (PVS1+PM2+PP3 ).@*CONCLUSION@#A novel splicing variant of FBN2 gene (c.533-1G>C) was identified, which can lead to congenital contractural arachnodactyly.

Expanding the phenotypic spectrum of Mendelian connective tissue disorders to include prominent kidney phenotypes.

Heritable connective tissue disorders are a group of diseases, each rare, characterized by various combinations of skin, joint, musculoskeletal, organ, and vascular involvement. Although kidney abnormalities have been reported in some connective tissue disorders, they are rarely a presenting feature. Here we present three patients with prominent kidney phenotypes who were found by whole exome sequencing to have variants in established connective tissue genes associated with Loeys-Dietz syndrome and congenital contractural arachnodactyly. These cases highlight the importance of considering connective tissue disease in children presenting with structural kidney disease and also serves to expand the phenotype of Loeys-Dietz syndrome and possibly congenital contractural arachnodactyly to include cystic kidney disease and cystic kidney dysplasia, respectively.

Arachnodactyly represented in art.

Arachnodactyly, a term used since 1902 to describe abnormally long (spider-like) fingers, is a pathologic feature of several heritable conditions, notably the Marfan syndrome and congenital contractural arachnodactyly. A number of prominent artists, dating from the 16th to the 20th centuries, have depicted subjects with unusually long fingers, sometime associated with elongation of the body, neck and head. El Greco incorporated this style in many paintings. Little evidence supports any subject in any of these paintings as having a congenital deformity.

Further delineation of van den Ende-Gupta syndrome: Genetic heterogeneity and overlap with congenital heart defects and skeletal malformations syndrome.

Van den Ende-Gupta syndrome (VDEGS) is a rare autosomal recessive condition characterized by distinctive facial and skeletal features, and in most affected persons, by biallelic pathogenic variants in SCARF2. We review the type and frequency of the clinical features in 36 reported individuals with features of VDEGS, 15 (42%) of whom had known pathogenic variants in SCARF2, 6 (16%) with negative SCARF2 testing, and 15 (42%) not tested. We also report three new individuals with pathogenic variants in SCARF2 and clinical features of VDEGS. Of the six persons without known pathogenic variants in SCARF2, three remain unsolved despite extensive genetic testing. Three were found to have pathogenic ABL1 variants using whole exome sequencing (WES) or whole genome sequencing (WGS). Their phenotype was consistent with the congenital heart disease and skeletal malformations syndrome (CHDSKM), which has been associated with ABL1 variants. Of the three unsolved cases, two were brothers who underwent WGS and targeted long-range sequencing of both SCARF2 and ABL1, and the third person who underwent WES and RNA sequencing for SCARF2. Because these affected individuals with classical features of VDEGS lacked a detectable pathogenic SCARF2 variant, genetic heterogeneity is likely. Our study shows the importance of performing genetic testing on individuals with the VDEGS "phenotype," either as a targeted gene analysis (SCARF2, ABL1) or WES/WGS. Additionally, individuals with the combination of arachnodactyly and blepharophimosis should undergo echocardiography while awaiting results of molecular testing due to the overlapping physical features of VDEGS and CHDSKM.

Mutation analysis and prenatal diagnosis of a family with congenital contractural arachnodactyly.

BACKGROUND: Congenital contractural arachnodactyly (CCA) is a rare autosomal dominant condition caused by mutations in the fibrillin 2 gene (FBN2). The primary clinical symptoms of CCA include multiple flexion contractures, arachnodactyly, dolichostenomelia, scoliosis, abnormal pinnae, muscular hypoplasia, and crumpled ears. METHODS: We used whole-exome sequencing technology to examine an arthrogryposis multiplex congenita and used Sanger sequencing technology to genetically confirm its family. RESULTS: FBN2 c.3344A>T(p.D1115V) was identified in this family with CCA in a pedigree. Prenatal diagnosis and counseling were carried out simultaneously to avoid the birth of the sick fetus. CONCLUSION: The study is on FBN2 variant in CCA, which potentially having implications for genetic counseling and clinical management, our study may provide new insights into the cause and diagnosis of CCA.

Severe congenital contractural arachnodactyly caused by biallelic pathogenic variants in FBN2.

Fibrillin-2, encoded by FBN2, plays an important role in the early process of elastic fiber assembly. To date, heterozygous pathogenic variants in FBN2 have been shown to cause congenital contractural arachnodactyly (CCA; Beals-Hecht syndrome). Classical CCA is characterized by long and slender fingers and toes, ear deformities, joint contractures at birth, clubfeet, muscular hypoplasia and often tall stature. In individuals with a severe CCA form, different cardiovascular or gastrointestinal anomalies have been described. Here, we report on a 15-year-old girl with a severe form of CCA and novel biallelic variants in FBN2. The girl inherited the missense variant c.3563G > T/p.(Gly1188Val) from her unaffected father and the nonsense variant c.6831C > A/p.(Cys2277*) from her healthy mother. We could detect only a small amount of FBN2 transcripts harboring the nonsense variant in leukocyte-derived mRNA from the patient and mother suggesting nonsense-mediated mRNA decay. As the father did not show any clinical signs of CCA we hypothesize the missense variant c.3563G > T to be a hypomorphic allele. Taken together, our data suggests that severe CCA can be inherited in an autosomal-recessive manner by compound heterozygosity of a hypomorphic and a null allele of the FBN2 gene.

Mutations in SKI in Shprintzen-Goldberg syndrome lead to attenuated TGF-ß responses through SKI stabilization.

Shprintzen-Goldberg syndrome (SGS) is a multisystemic connective tissue disorder, with considerable clinical overlap with Marfan and Loeys-Dietz syndromes. These syndromes have commonly been associated with enhanced TGF-ß signaling. In SGS patients, heterozygous point mutations have been mapped to the transcriptional co-repressor SKI, which is a negative regulator of TGF-ß signaling that is rapidly degraded upon ligand stimulation. The molecular consequences of these mutations, however, are not understood. Here we use a combination of structural biology, genome editing, and biochemistry to show that SGS mutations in SKI abolish its binding to phosphorylated SMAD2 and SMAD3. This results in stabilization of SKI and consequently attenuation of TGF-ß responses, both in knockin cells expressing an SGS mutation and in fibroblasts from SGS patients. Thus, we reveal that SGS is associated with an attenuation of TGF-ß-induced transcriptional responses, and not enhancement, which has important implications for other Marfan-related syndromes.

Confirming the involvement of PIEZO2 in the etiology of Marden-Walker syndrome.

Pathogenic heterozygous variants in PIEZO2 typically cause distal arthrogryposis type 5 (DA5) and the closely related Gordon syndrome (GS). Only one case of PIEZO2-related Marden-Walker syndrome (MWS) has been reported to date. We report the phenotypic features of a Saudi female patient with features consistent with MWS in whom we identified a novel de novo likely pathogenic variant in PIEZO2. Our case lends support to the link between PIEZO2 and MWS.

Based on a cohort of 52,879 microarrays, recurrent intragenic FBN2 deletion encompassing exons 1-8 does not cause Beals syndrome.

INTRODUCTION: Congenital contractural arachnodactyly (CCA) is a rare connective tissue disorder, associated with heterozygous mutations in the FBN2 gene. The objective of this study was to evaluate the prevalence of an intragenic deletion encompassing exons 1-8 of FBN2 gene in Israeli population. MATERIALS AND METHODS: A search for intragenic FBN2 microdeletions was performed in two databases of chromosomal microarray analysis (CMA) - genetic laboratory of a tertiary medical center (the primary cohort) and one of the largest Israeli health maintenance organizations (replication cohort). RESULTS: Overall, 52,879 microarray tests were searched for FBN2 microdeletions. The primary cohort constituted of 18,301 CMA tests, among which 33 intragenic FBN2 microdeletions in unrelated individuals were found (0.18%). Prenatal prevalence of this variant was 0.23% (28/12,604), and specifically in low risk pregnancies - 0.29% (22/7464). Of the 28 cases with known parental origin, 27 (96.4%) were of full or partial Ashkenazi Jewish ethnic background. The approximate allele incidence in the Ashkenazi Jewish origin was 0.4% (18/4961). Combined with the 34,578 CMA tests in the replication cohort, the overall frequency of FBN2 microdeletions was 0.24% (125/52,879). None of the pre- or postnatal cases had any clinical manifestations of CCA. DISCUSSION: Intragenic FBN2 microdeletions are found in one of every 420 CMA analyses in Israeli population, and in particular one of every 340 low-risk pregnancies. Due to high allele incidence in Ashkenazi Jewish population (1:275), we suggest that FBN2 gene deletion detected by CMA among Ashkenazi Jews should be interpreted as benign copy number variant.

The Genetic Epidemiology of Pediatric Pulmonary Arterial Hypertension.

OBJECTIVE: To describe the prevalence of pulmonary arterial hypertension (PAH)-associated gene mutations, and other genetic characteristics in a national cohort of children with PAH from the Dutch National registry and to explore genotype-phenotype associations and outcomes. STUDY DESIGN: Children (n = 70) diagnosed with idiopathic PAH, heritable PAH, PAH associated with congenital heart disease with coincidental shunt (PAH-congenital heart disease group 3), PAH after closure of a cardiac shunt (PAH-congenital heart disease group 4), or PAH associated with other noncardiac conditions were enrolled. Targeted next-generation sequencing was performed on PAH-associated genes (BMPR2, ACVRL1, EIF2AK4, CAV1, ENG, KCNK3, SMAD9, and TBX4). Also, children were tested for specific genetic disorders in case of clinical suspicion. Additionally, children were tested for copy number variations. RESULTS: Nineteen children (27%) had a PAH-associated gene mutation/variant: BMPR2 n = 7, TBX4 n = 8, ACVRL1 n = 1, KCNK3 n = 1, and EIF2AK4 n = 2. Twelve children (17%) had a genetic disorder with an established association with PAH (including trisomy 21 and cobalamin C deficiency). In another 16 children (23%), genetic disorders without an established association with PAH were identified (including Noonan syndrome, Beals syndrome, and various copy number variations). Survival rates differed between groups and was most favorable in TBX4 variant carriers. CONCLUSIONS: Children with PAH show a high prevalence of genetic disorders, not restricted to established PAH-associated genes. Genetic architecture could play a role in risk-stratified care management in pediatric PAH.

Double heterozygous variants in FBN1 and FBN2 in a Thai woman with Marfan and Beals syndromes.

A phenotype of an individual is resulted from an interaction among variants in several genes. Advanced molecular technologies allow us to identify more patients with mutations in more than one genes. Here, we studied a Thai woman with combined clinical features of Marfan (MFS) and Beals (BS) syndromes including frontal bossing, enophthalmos, myopia, the crumpled appearance to the top of the pinnae, midface hypoplasia, high arched palate, dermal stretch marks, aortic enlargement, mitral valve prolapse and regurgitation, aortic root dilatation, and progressive scoliosis. The aortic root enlargement was progressive to a diameter of 7.2 cm requiring an aortic root replacement at the age of 8 years. At her last visit when she was 19 years old, she had moderate aortic regurgitation. Exome sequencing revealed that she carried the c.3159C > G (p.Cys1053Trp) in exon 26 of FBN1 and c.2638G > A (p. Gly880Ser) in exon 20 of FBN2. The variant in FBN1 was de novo, while that in FBN2 was inherited from her unaffected mother. Both genes encode for fibrillins, which are essential for elastic fibers and can form the heterotypic microfibrils. Two defective fibrillins may synergistically worsen cardiovascular manifestations seen in our patient. In this study, we identified the fourth patient with both MFS and BS, carrying mutations in both FBN1 and FBN2.

[Pathological variant of FBN2 gene identified in a pedigree affected with congenital contracture arachnodactyly].

OBJECTIVE: To detect pathological variant in a Chinese pedigree affected with congenital contractural arachnodactyly (CCA). METHODS: Next generation sequencing (NGS) was used to scan the whole exome of the proband. Potential variant of the FBN2 gene was also detected in all members of the pedigree and 100 healthy controls by Sanger sequencing. With the determination of the genotype, prenatal diagnosis was carried out by amniotic fluid sampling. RESULTS: A c.3528C>A (p.Asn1176Lys) variant was identified in the FBN2 gene of the proband, other patients from this pedigree, as well as the fetus. The same variant was not found among healthy members from this pedigree and the 100 healthy controls. CONCLUSION: The c.3528C>A (p.Asn1176Lys) variant of the FBN2 gene probably underlies the pathogenesis of CCA in our case. The new variant has enriched pathological spectrum of the FBN2 gene.

Role of fibrillin-2 in the control of TGF-ß activation in tumor angiogenesis and connective tissue disorders.

Fibrillins constitute a family of large extracellular glycoproteins which multimerize to form microfibrils, an important structure in the extracellular matrix. It has long been assumed that fibrillin-2 was barely present during postnatal life, but it is now clear that fibrillin-2 molecules form the structural core of microfibrils, and are masked by an outer layer of fibrillin-1. Mutations in fibrillins give rise to heritable connective tissue disorders, including Marfan syndrome and congenital contractural arachnodactyly. Fibrillins also play an important role in matrix sequestering of members of the transforming growth factor-ß family, and in context of Marfan syndrome excessive TGF-ß activation has been observed. TGF-ß activation is highly dependent on integrin binding, including integrin αvß8 and αvß6, which are upregulated upon TGF-ß exposure. TGF-ß is also involved in tumor progression, metastasis, epithelial-to-mesenchymal transition and tumor angiogenesis. In several highly vascularized types of cancer such as hepatocellular carcinoma, a positive correlation was found between increased TGF-ß plasma concentrations and tumor vascularity. Interestingly, fibrillin-1 has a higher affinity to TGF-ß and, therefore, has a higher capacity to sequester TGF-ß compared to fibrillin-2. The previously reported downregulation of fibrillin-1 in tumor endothelium affects the fibrillin-1/fibrillin-2 ratio in the microfibrils, exposing the normally hidden fibrillin-2. We postulate that fibrillin-2 exposure in the tumor endothelium directly stimulates tumor angiogenesis by influencing TGF-ß sequestering by microfibrils, leading to a locally higher active TGF-ß concentration in the tumor microenvironment. From a therapeutic perspective, fibrillin-2 might serve as a potential target for future anti-cancer therapies.