Delineation of a new fibrillino-2-pathy with evidence for a role of FBN2 in the pathogenesis of carpal tunnel syndrome

Whole-exome sequencing identifies 5 novel genes associated with carpal tunnel syndrome

Carpal tunnel syndrome (CTS), a common peripheral nerve entrapment disorder, has a high estimated heritability index. Although previous genome-wide association studies have assessed common genetic components of CTS, the risk contributed by coding variants is still not well understood. Here, we performed the largest exome-wide analyses using UK Biobank data from 350 770 participants to find coding variants associated with CTS. We then explored the relative contribution of both rare mutations and polygenic risk score (PRS) to CTS risk in survival analyses. Finally, we investigated the functional pathways of the CTS-related coding genes identified above. Aside from conforming 6 known CTS genes, 5 novel genes were identified (SPSB1, SYNC, ITGB5, MUC13 and LOXL4). The associations of most genes we identified with incident CTS were striking in survival analyses. Additionally, we provided evidence that combining rare coding alleles and polygenic risk score can improve the genetic prediction of CTS. Functional enrichment analyses revealed potential roles of the identified coding variants in CTS pathogenesis, where they contributed to extracellular matrix organization. Our results evaluated the contribution to CTS etiology from quantities of coding variants accessible to exome sequencing data.

Short stature, brachydactyly and joint contractures associated with novel FBN2 variants in two families

BACKGROUND

Fibrillinopathies comprise allelic disorders with opposing phenotypes. Pathogenic variants in fibrillin-2, encoded by FBN2, have mainly been associated with congenital contractural arachnodactyly but in a few cases also with brachydactyly.

METHODS AND RESULTS

We recruited two families with index patients presenting with short stature (heights ≤3 SD scores), brachydactyly, joint contractures and facial dysmorphism as major features. In Family 2, the proband and father also had carpal tunnel syndrome. Radiographs showed signs of mild skeletal dysplasia with short long bones, brachydactyly and mild metaphyseal and vertebral irregularity. Whole genome sequencing revealed novel variants in the FBN2 gene that segregated with the phenotype: in Family 1, a novel heterozygous missense variant c.4862G>A, p.(Cys1621Tyr) and in Family 2, a novel heterozygous deletion of exons 9-11. The missense variant affects a highly conserved residue and is predicted to be deleterious by most in silico tools. The FBN2 deletion affects a well-conserved region and leads to loss of the transforming growth factor β binding-like 2 domain and part of the calcium-binding epidermal growth factor-like domain.

CONCLUSION

Our findings suggest that short stature and mild skeletal dysplasia might be part of the spectrum of FBN2-related phenotypes. The study supports the role of FBN2 variants in growth failure and expands the molecular spectrum of FBN2 variants.

FBN2 pathogenic mutation in congenital contractural arachnodactyly with severe skeletal manifestations

Background

Congenital contractural arachnodactyly (CCA) is a rare autosomal dominant connective tissue disorder caused by mutations in the fibrillin-2 (FBN2) gene, characterized by crumpled ears, arachnodactyly, camptodactyly, dolichostenomelia, large-joint contractures and thoracolumbar scoliosis. Variations in the FBN2 gene primarily include missense mutations and splice sites mutations. It is crucial to clarify whether missense mutations in the FBN2 gene affect mRNA splicing.

Methods

We identified a novel pathogenic missense variant (c.3472G > C, p.Asp1158His) in exon 26 of the FBN2 gene using whole-exome sequencing (WES) and Sanger sequencing. In vitro, both the wild-type and mutant minigenes were successfully inserted into the pcMINI and pcMINI-C vectors to verify the impact of this variant on FBN2 mRNA splicing. We utilized CLUSTALW to perform multiple sequence alignment to compare the evolutionary conservation of this variant and employed AlphaFold2 to predict the protein structure of the mutant.

Results

The likely pathogenic missense mutation (c.3472G > C) results in the amino acid at position 1158 of the FBN2 changing from aspartic acid (Asp) to histidine (His). Furthermore, DNA multiple sequence alignment indicates that this site is highly evolutionarily conserved. Functional assays and structure prediction indicated that the missense variant located at the edge of exon 26 of FBN2 does not affect RNA splicing, instead, it changes the structure and function of the protein by altering the amino acid sequence.

Conclusion

This study enriches the pathogenic spectrum of CCA. Our research provides new insights for the diagnosis of CCA and may have an impact on genetic counseling.

Genomic variations associated with risk and protection against vincristine-induced peripheral neuropathy in pediatric cancer patients

Vincristine-induced peripheral neuropathy is a common and highly debilitating toxicity from vincristine treatment that affects quality of life and often requires dose reduction, potentially affecting survival. Although previous studies demonstrated genetic factors are associated with vincristine neuropathy risk, the clinical relevance of most identified variants is limited by small sample sizes and unclear clinical phenotypes. A genome-wide association study was conducted in 1100 cases and controls matched by vincristine dose and genetic ancestry, uncovering a statistically significant (p < 5.0 × 10-8) variant in MCM3AP gene that substantially increases the risk of neuropathy and 12 variants protective against neuropathy within/near SPDYA, METTL8, PDE4D, FBN2, ZFAND3, NFIB, PAPPA, LRRTM3, NRG3, VTI1A, ARHGAP5, and ACTN1. A follow-up pathway analysis reveals the involvement of four key pathways, including nerve structure and development, myelination, neuronal transmission, and cytoskeleton/microfibril function pathways. These findings present potential actionable genomic markers of vincristine neuropathy and offer opportunities for tailored interventions to improve vincristine safety in children with cancer. This study is registered with ClinicalTrials.gov under the title National Active Surveillance Network and Pharmacogenomics of Adverse Drug Reactions in Children (ID NCT00414115, registered on December 21, 2006).

Pathophysiology, Diagnosis, Treatment, and Genetics of Carpal Tunnel Syndrome: A Review

Carpal tunnel syndrome (CTS) is a common peripheral canalicular nerve entrapment syndrome in the upper extremities. The compression of or injury to the median nerve at the wrist as it passes through a space-limited osteofibrous carpal canal can cause CTS, resulting in hand pain and impaired function. The present paper reviews the literature on the prevalence, pathology, diagnosis, treatment, and risk factors of CTS in conjunction with the role of genetic factors in CTS etiology. CTS diagnosis is primarily linked with clinical symptoms; still, it is simplified by sophisticated approaches such as magnetic resonance imaging and ultrasonography. CTS symptoms can be ameliorated through conservative and surgical strategies. The exact CTS pathophysiology needs clarification. Genetic predispositions to CTS are augmented by various variants within genes; however, CTS etiology could include risk factors such as wrist movements, injury, and specific conditions (e.g., age, body mass index, sex, and cardiovascular conditions). The high prevalence of CTS diminishes the quality of life of its sufferers and imposes costs on health systems, hence the significance of research and clinical trials to elucidate CTS pathogenesis and develop novel therapeutic targets.

Case report: Identification of novel fibrillin-2 variants impacting disulfide bond and causing congenital contractural arachnodactyly

Background: Congenital contractural arachnodactyly (CCA) is an autosomal dominant connective tissue disorder with clinical features of arthrogryposis, arachnodactyly, crumpled ears, scoliosis, and muscular hypoplasia. The heterozygous pathogenic variants in FBN2 have been shown to cause CCA. Fibrillin-2 is related to the elasticity of the tissue and has been demonstrated to play an important role in the constitution of extracellular microfibrils in elastic fibers, providing strength and flexibility to the connective tissue that sustains the body's joints and organs. Methods: We recruited two Chinese families with arachnodactyly and bilateral arthrogryposis of the fingers. Whole-exome sequencing (WES) and co-segregation analysis were employed to identify their genetic etiologies. Three-dimensional protein models were used to analyze the pathogenic mechanism of the identified variants. Results: We have reported two CCA families and identified two novel missense variants in FBN2 (NM_001999.3: c.4093T>C, p.C1365R and c.2384G>T, p.C795F). The structural models of the mutant FBN2 protein in rats exhibited that both the variants could break disulfide bonds. Conclusion: We detected two FBN2 variants in two families with CCA. Our description expands the genetic profile of CCA and emphasizes the pathogenicity of disulfide bond disruption in FBN2.

The fibrillinopathies: new insights with focus on the paradigm of opposing phenotypes for both FBN1 and FBN2

Different pathogenic variants in the fibrillin‐1 gene (FBN1) cause Marfan syndrome and acromelic dysplasias. Whereas the musculoskeletal features of Marfan syndrome involve tall stature, arachnodactyly, joint hypermobility, and muscle hypoplasia, acromelic dysplasia patients present with short stature, brachydactyly, stiff joints, and hypermuscularity. Similarly, pathogenic variants in the fibrillin‐2 gene (FBN2) cause either a Marfanoid congenital contractural arachnodactyly or a FBN2‐related acromelic dysplasia that most prominently presents with brachydactyly. The phenotypic and molecular resemblances between both the FBN1 and FBN2‐related disorders suggest that reciprocal pathomechanistic lessons can be learned. In this review, we provide an updated overview and comparison of the phenotypic and mutational spectra of both the “tall” and “short” fibrillinopathies. The future parallel functional study of both FBN1/2‐related disorders will reveal new insights into how pathogenic fibrillin variants differently affect the fibrillin microfibril network and/or growth factor homeostasis in clinically opposite syndromes. This knowledge may eventually be translated into new therapeutic approaches by targeting or modulating the fibrillin microfibril network and/or the signaling pathways under its control.

Bi-allelic premature truncating variants in LTBP1 cause cutis laxa syndrome

Latent transforming growth factor β (TGFβ)-binding proteins (LTBPs) are microfibril-associated proteins essential for anchoring TGFβ in the extracellular matrix (ECM) as well as for correct assembly of ECM components. Variants in LTBP2, LTBP3, and LTBP4 have been identified in several autosomal recessive Mendelian disorders with skeletal abnormalities with or without impaired development of elastin-rich tissues. Thus far, the human phenotype associated with LTBP1 deficiency has remained enigmatic. In this study, we report homozygous premature truncating LTBP1 variants in eight affected individuals from four unrelated consanguineous families. Affected individuals present with connective tissue features (cutis laxa and inguinal hernia), craniofacial dysmorphology, variable heart defects, and prominent skeletal features (craniosynostosis, short stature, brachydactyly, and syndactyly). In vitro studies on proband-derived dermal fibroblasts indicate distinct molecular mechanisms depending on the position of the variant in LTBP1. C-terminal variants lead to an altered LTBP1 loosely anchored in the microfibrillar network and cause increased ECM deposition in cultured fibroblasts associated with excessive TGFβ growth factor activation and signaling. In contrast, N-terminal truncation results in a loss of LTBP1 that does not alter TGFβ levels or ECM assembly. In vivo validation with two independent zebrafish lines carrying mutations in ltbp1 induce abnormal collagen fibrillogenesis in skin and intervertebral ligaments and ectopic bone formation on the vertebrae. In addition, one of the mutant zebrafish lines shows voluminous and hypo-mineralized vertebrae. Overall, our findings in humans and zebrafish show that LTBP1 function is crucial for skin and bone ECM assembly and homeostasis.