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.

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.

Along came a spider: Medicine's most famous spider eponyms.

Spiders have long been admired for the beauty of their webs. They are celebrated in popular culture as well as in medical eponyms. This contribution provides the historical background for three spider-related eponyms: nevus araneus (spider angioma), arachnodactyly, and the arachnoid mater. Nevus araneus was first named and described by Sir Erasmus Wilson in 1842. Arachnodactyly was described in 1896 by Antoine Marfan using the term pattes d'araignée, which means spider legs. In 1902, Emile Charles Achard proposed the term arachnodactyly for this clinical finding. The arachnoid mater had been named in 1699 by Frederik Ruysch. The clinical management of spider bites from the only two dangerous venomous spiders within the United States, the black widow spider (Latrodectus mactans) and the brown recluse spider (Loxosceles reclusa), is reviewed.

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.

Further Defining the Phenotypic Spectrum of B3GAT3 Mutations and Literature Review on Linkeropathy Syndromes.

The term linkeropathies (LKs) refers to a group of rare heritable connective tissue disorders, characterized by a variable degree of short stature, skeletal dysplasia, joint laxity, cutaneous anomalies, dysmorphism, heart malformation, and developmental delay. The LK genes encode for enzymes that add glycosaminoglycan chains onto proteoglycans via a common tetrasaccharide linker region. Biallelic variants in XYLT1 and XYLT2, encoding xylosyltransferases, are associated with Desbuquois dysplasia type 2 and spondylo-ocular syndrome, respectively. Defects in B4GALT7 and B3GALT6, encoding galactosyltransferases, lead to spondylodysplastic Ehlers-Danlos syndrome (spEDS). Mutations in B3GAT3, encoding a glucuronyltransferase, were described in 25 patients from 12 families with variable phenotypes resembling Larsen, Antley-Bixler, Shprintzen-Goldberg, and Geroderma osteodysplastica syndromes. Herein, we report on a 13-year-old girl with a clinical presentation suggestive of spEDS, according to the 2017 EDS nosology, in whom compound heterozygosity for two B3GAT3 likely pathogenic variants was identified. We review the spectrum of B3GAT3-related disorders and provide a comparison of all LK patients reported up to now, highlighting that LKs are a phenotypic continuum bridging EDS and skeletal disorders, hence offering future nosologic perspectives.

The clinical application of preimplantation genetic diagnosis for the patient affected by congenital contractural arachnodactyly and spinal and bulbar muscular atrophy.

PURPOSE: To investigate the usefulness of preimplantation genetic diagnosis (PGD) for the patient affected by congenital contractural arachnodactyly (CCA) and spinal and bulbar muscular atrophy (SBMA). METHODS: Multiple displacement amplification (MDA) was performed for whole genome amplification (WGA) of biopsied trophectoderm (TE) cells. Direct mutation detection by sequencing and next-generation sequencing (NGS)-based single nucleotide polymorphism (SNP) haplotyping were used for CCA diagnosis. Direct sequencing of the PCR products and sex determination by amplification of sex-determining region Y (SRY) gene were used for SBMA diagnosis. After PGD, the unaffected blastocyst (B4) was transferred in the following frozen embryo transfer (FET). RESULTS: In this PGD cycle, sixteen MII oocytes were inseminated by ICSI with testicular spermatozoa. Four blastocysts (B4, B5, B10, B13) were utilized for TE cell biopsy on day 5 after ICSI. After PGD, B4 was unaffected by CCA and SBMA. B5 was affected by CCA and carried SBMA. B10 was unaffected by CCA and carried SBMA. B13 was affected by CCA and unaffected by SBMA. B4 was the only unaffected blastocyst and transferred into the uterus for the subsequent FET cycle. The accuracy of PGD was confirmed by amniocentesis at 21 weeks of gestation. A healthy boy weighing 2850 g was born by cesarean section at the 38th week of gestation. CONCLUSIONS: PGD is a valid screening tool for patienst affected of CCA and SBMA to prevent transmission of these genetic diseases from parents to children.

Fibrillin microfibrils in bone physiology.

The severe skeletal abnormalities associated with Marfan syndrome (MFS) and congenital contractural arachnodactyly (CCA) underscore the notion that fibrillin assemblies (microfibrils and elastic fibers) play a critical role in bone formation and function in spite of representing a low abundance component of skeletal matrices. Studies of MFS and CCA mice have correlated the skeletal phenotypes of these mutant animals with distinct pathophysiological mechanisms that reflect the contextual contribution of fibrillin-1 and -2 scaffolds to TGFß and BMP signaling during bone patterning, growth and metabolism. Illustrative examples include the unique role of fibrillin-2 in regulating BMP-dependent limb patterning and the distinct impact of the two fibrillin proteins on the commitment and differentiation of marrow mesenchymal stem cells. Collectively, these findings have important implication for our understanding of the pathophysiological mechanisms that drive age- and injury-related processes of bone degeneration.

A novel homozygous mutation in FGFR3 causes tall stature, severe lateral tibial deviation, scoliosis, hearing impairment, camptodactyly, and arachnodactyly.

Most reported mutations in the FGFR3 gene are dominant activating mutations that cause a variety of short-limbed bone dysplasias including achondroplasia and syndromic craniosynostosis. We report the phenotype and underlying molecular abnormality in two brothers, born to first cousin parents. The clinical picture is characterized by tall stature and severe skeletal abnormalities leading to inability to walk, with camptodactyly, arachnodactyly, and scoliosis. Whole exome sequencing revealed a homozygous novel missense mutation in the FGFR3 gene in exon 12 (NM_000142.4:c.1637C>A: p.(Thr546Lys)). The variant is found in the kinase domain of the protein and is predicted to be pathogenic. It is located near a known hotspot for hypochondroplasia. This is the first report of a homozygous loss-of-function mutation in FGFR3 in human that results in a skeletal overgrowth syndrome.

Marfan syndrome and sudden death within a family - aetiologic, molecular and diagnostic issues at autopsy.

Although Marfan syndrome has a range of characteristic morphological features involving the ocular, cardiovascular and musculoskeletal systems, the phenotype is variable. In addition, mutations have been identified in the gene encoding for fibrillin-1 and also in the transforming growth factor-beta receptor 2 (TGF-betaR2) gene. Two cases are presented of sudden and unexpected deaths in cousins who manifested morphologic features of Marfan syndrome at autopsy. Case 1: A 36-year-old male who collapsed and was found at autopsy to have arachnodactyly, a high arched palate and lethal aortic dissection with haemopericardium. Case 2: A 34-year-old male who collapsed and was found at autopsy to have arachnodactyly, a high arched palate, pes cavus and a dysplastic mitral valve. Current aetiological theories and molecular findings are discussed. While family follow-up and counselling are advised when cases come to autopsy, given the variability in phenotype and genotype, and the difficulties that exist in attempting to determine clinical prognosis from either of these, such deaths may raise more concerns for surviving family members than providing answers.