Cardiac anomalies complicating congenital contractural arachnodactyly

FBN2 pathogenic variants in congenital contractural arachnodactyly with severe cardiovascular manifestations

PURPOSE

Congenital contractural arachnodactyly (CCA) is an extremely rare autosomal dominant connective tissue genetic disorder caused by pathogenic variants in FBN2. CCA is characterized by arachnodactyly, camptodactyly, contracture of major joints, scoliosis, pectus deformities, and crumpled ears, but rarely with lethal cardiovascular manifestations as in Marfan syndrome. It is imperative to conduct a comprehensive analysis and review of the pathogenesis of CCA resulting from pathogenic variants in FBN2 gene.

MATERIALS AND METHODS

Using whole-exome sequencing and Sanger sequencing, we identified a novel pathogenic splice-altering variant (c.4472-3C>A) in intron 34 of FBN2 gene in a CCA pedigree. The transcriptional result of the splicing-altering variant was analyzed by RNA sequencing. We systematically analyzed the clinical manifestations of all reported cases of CCA caused by splicing-altering pathogenic variants and focused on all the pathogenic variants in FBN2 gene that are associated with severe cardiovascular manifestations.

RESULTS

The splice-altering variant (c.4472-3C>A) in FBN2 was demonstrated to result in the exon 35 skipping and cause an in-frame deletion. Furthermore, we identified exons 31 to 35 may be a hotspot region in FBN2 gene associated with severe cardiovascular phenotype.

CONCLUSIONS

This study enriched the pathogenic spectrum of CCA and identified a hotspot region in FBN2 gene associated with severe cardiovascular manifestations. We recommend that patients carrying pathogenic variants in exons 31 to 35 of FBN2 pay more attention to cardiac evaluation.

Delineation of dual molecular diagnosis in patients with skeletal deformity

Background

Skeletal deformity is characterized by an abnormal anatomical structure of bone and cartilage. In our previous studies, we have found that a substantial proportion of patients with skeletal deformity could be explained by monogenic disorders. More recently, complex phenotypes caused by more than one genetic defect (i.e., dual molecular diagnosis) have also been reported in skeletal deformities and may complicate the diagnostic odyssey of patients. In this study, we report the molecular and phenotypic characteristics of patients with dual molecular diagnosis and variable skeletal deformities.

Results

From 1108 patients who underwent exome sequencing, we identified eight probands with dual molecular diagnosis and variable skeletal deformities. All eight patients had dual diagnosis consisting of two autosomal dominant diseases. A total of 16 variants in 12 genes were identified, 5 of which were of de novo origin. Patients with dual molecular diagnosis presented blended phenotypes of two genetic diseases. Mendelian disorders occurred more than once include Osteogenesis Imperfecta Type I (COL1A1, MIM:166200), Neurofibromatosis, Type I (NF1, MIM:162200) and Marfan Syndrome (FBN1, MIM:154700).

Conclusions

This study demonstrated the complicated skeletal phenotypes associated with dual molecular diagnosis. Exome sequencing represents a powerful tool to detect such complex conditions.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13023-022-02293-x.

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.

A clinical scoring system for congenital contractural arachnodactyly

PURPOSE

Congenital contractural arachnodactyly (CCA) is an autosomal dominant connective tissue disorder manifesting joint contractures, arachnodactyly, crumpled ears, and kyphoscoliosis as main features. Due to its rarity, rather aspecific clinical presentation, and overlap with other conditions including Marfan syndrome, the diagnosis is challenging, but important for prognosis and clinical management. CCA is caused by pathogenic variants in FBN2, encoding fibrillin-2, but locus heterogeneity has been suggested. We designed a clinical scoring system and diagnostic criteria to support the diagnostic process and guide molecular genetic testing.

METHODS

In this retrospective study, we assessed 167 probands referred for FBN2 analysis and classified them into a FBN2-positive (n = 44) and FBN2-negative group (n = 123) following molecular analysis. We developed a 20-point weighted clinical scoring system based on the prevalence of ten main clinical characteristics of CCA in both groups.

RESULTS

The total score was significantly different between the groups (P < 0.001) and was indicative for classifying patients into unlikely CCA (total score <7) and likely CCA (total score ≥7) groups.

CONCLUSIONS

Our clinical score is helpful for clinical guidance for patients suspected to have CCA, and provides a quantitative tool for phenotyping in research settings.

Dilatation of the great arteries in an infant with marfan syndrome and ventricular septal defect

We describe an infant presenting with contractures of the fingers, a large ventricular septal defect (VSD), and severe pulmonary artery dilatation. He had clinical and echocardiographic features of both neonatal or infantile Marfan syndrome (MFS) and congenital contractural arachnodactyly. After surgical VSD closure, the aortic root developed progressive dilatation while the size of pulmonary artery returned to normal limits. Eventually the diagnosis of MFS was confirmed by DNA analysis.

Comprehensive clinical and molecular assessment of 32 probands with congenital contractural arachnodactyly: report of 14 novel mutations and review of the literature

Beals-Hecht syndrome or congenital contractural arachnodactyly (CCA) is a rare, autosomal dominant connective tissue disorder characterized by crumpled ears, arachnodactyly, contractures, and scoliosis. Recent reports also mention aortic root dilatation, a finding previously thought to differentiate the condition from Marfan syndrome (MFS). In many cases, the condition is caused by mutations in the fibrillin 2 gene (FBN2) with 26 mutations reported so far, all located in the middle region of the gene (exons 23-34). We directly sequenced the entire FBN2 gene in 32 probands clinically diagnosed with CCA. In 14 probands, we found 13 new and one previously described FBN2 mutation including a mutation in exon 17, expanding the region in which FBN2 mutations occur in CCA. Review of the literature showed that the phenotype of the FBN2 positive patients was comparable to all previously published FBN2-positive patients. In our FBN2-positive patients, cardiovascular involvement included mitral valve prolapse in two adult patients and aortic root enlargement in three patients. Whereas the dilatation regressed in one proband, it remained marked in a child proband (z-score: 4.09) and his father (z-score: 2.94), warranting echocardiographic follow-up. We confirm paradoxical patellar laxity and report keratoconus, shoulder muscle hypoplasia, and pyeloureteral junction stenosis as new features. In addition, we illustrate large intrafamilial variability. Finally, the FBN2-negative patients in this cohort were clinically indistinguishable from all published FBN2-positive patients harboring a FBN2 mutation, suggesting locus heterogeneity.

The FBN2 gene: new mutations, locus-specific database (Universal Mutation Database FBN2), and genotype-phenotype correlations

Congenital contractural arachnodactyly (CCA) is an extremely rare disease, due to mutations in the FBN2 gene encoding fibrillin-2. Another member of the fibrillin family, the FBN1 gene, is involved in a broad phenotypic continuum of connective-tissue disorders including Marfan syndrome. Identifying not only what is in common but also what differentiates these two proteins should enable us to better comprehend their respective functions and better understand the multitude of diseases in which these two genes are involved. In 1995 we created a locus-specific database (LSDB) for FBN1 mutations with the Universal Mutation Database (UMD) tool. To facilitate comparison of identified mutations in these two genes and search for specific functional areas, we created an LSDB for the FBN2 gene: the UMD-FBN2 database. This database lists 26 published and six newly identified mutations that mainly comprise missense and splice-site mutations. Although the number of described FBN2 mutations was low, the frequency of joint dislocation was significantly higher with missense mutations when compared to splice site mutations.

Long-term survival in a child with severe congenital contractural arachnodactyly, autism and severe intellectual disability

The severe form of congenital contractural arachnodactyly is usually associated with early mortality due to multisystem complications. Here, we report a 9-year-old male child with severe skeletal manifestations of congenital contractural arachnodactyly. He had none of the cardiovascular or gastrointestinal features that have been described in severe congenital contractural arachnodactyly. He had profound intellectual disability with autism. All exons of FBN2, the gene associated with congenital contractural arachnodactyly, were sequenced and no disease-causing mutation was found. When severe congenital contractural arachnodactyly is diagnosed in the newborn period, parents need to be aware that long-term survival is possible, particularly if no significant extraskeletal complications are present, and that significant neurodevelopmental delay may occur.

Congenital diaphragmatic eventration and bilateral uretero-hydronephrosis in a patient with neonatal Marfan syndrome caused by a mutation in exon 25 of the FBN1 gene and review of the literature

Neonatal Marfan syndrome, the most severe presentation of Marfan syndrome phenotypes (MIM 154700), is characterised mainly by joint contractures, arachnodactyly, loose skin, crumpled ears, severe atrioventricular valve dysfunction and pulmonary emphysema. Death usually occurs within the first 2 years of life from congestive heart failure. We describe here a newborn male with many typical characteristics of neonatal Marfan syndrome associated with a diaphragmatic eventration and a bilateral uretero-hydronephrosis with bladder dilatation. He died from cardiac failure due to severe tricuspid and mitral regurgitation at 62 h of age.

CONCLUSION

Molecular analysis showed a heterozygous missense mutation at nucleotide 3165 (3165T>G) in exon 25 of the FBN1 gene, resulting in the substitution of cysteine for tryptophan (C1055W).

Prenatal ultrasound findings in a fetus with congenital contractural arachnodactyly

Congenital contractural arachnodactyly (CCA) or Beals-Hecht syndrome is an autosomal dominant disorder caused by mutations in the fibrillin-2 (FBN2) gene. The principal features of CCA are a marfanoid habitus, multiple congenital contractures, camptodactyly, arachnodactyly, kyphoscoliosis, muscular hypoplasia, and external ear malformations. Our case is the first that shows typical sonographic signs in a fetus at 25 weeks' gestation with molecular genetically verified CCA in a large family with many members affected over four generations. This demonstrates that CCA can be detected prenatally by non-invasive ultrasonography. The importance of confirmation of CCA by means of DNA sequence analysis of the FBN2 gene is stressed.

Congenital contractural arachnodactyly with neurogenic muscular atrophy: case report

We report the case of a 3-(1/2)-year-old girl with hypotonia, multiple joint contractures, hip luxation, arachnodactyly, adducted thumbs, dolichostenomelia, and abnormal external ears suggesting the diagnosis of congenital contractural arachnodactyly (CCA). The serum muscle enzymes were normal and the needle electromyography showed active and chronic denervation. The muscle biopsy demonstrated active and chronic denervation compatible with spinal muscular atrophy. Analysis of exons 7 and 8 of survival motor neuron gene through polymerase chain reaction did not show deletions. Neurogenic muscular atrophy is a new abnormality associated with CCA, suggesting that CCA is clinically heterogeneous.

Prenatal diagnosis in congenital contractural arachnodactyly

Congenital contractural arachnodactyly (CCA) is a heritable connective tissue disorder caused by defects in the gene encoding fibrillin-2 (FBN2). People with CCA typically have a marfanoid habitus, flexion contractures, severe kyphoscoliosis, abnormal pinnae, and muscular hypoplasia. Because of the relative infrequency of the syndrome and its generally mild to moderate severity, prenatal diagnosis had not previously been sought. Here we report prenatal diagnosis in a family with CCA. Because the course of the disease in the proband was rather severe, she had requested genetic counseling as early as age 17. She delayed childbearing until prenatal diagnosis for CCA became possible. This decision was supported by her mother and later her husband. Because she shared the same genotype with her husband, genetic linkage analysis of this family did not alter the a priori 50% risk of having an affected child. The possibility of unambiguously ascertaining the affected status of a fetus homozygous for the tested FBN2 marker was sufficient for the family to pursue prenatal diagnosis. This case strongly points to the importance of informed decisions now that genetic testing is becoming commonplace.

Identification of the developmental marker, JB3-antigen, as fibrillin-2 and its de novo organization into embryonic microfibrous arrays

The monoclonal antibody JB3 was previously shown to react with a protein antigen present in the bilateral primitive heart-forming regions and septation-stage embryonic hearts; in addition, primary axial structures at primitive streak stages are JB3-immunopositive (Wunsch et al. [1994] Dev. Biol. 165:585-601). The JB3 antigen has an overlapping distribution pattern with fibrillin-1, and a similar molecular mass (Gallagher et al. [1993] Dev. Dyn. 196:70-78; Wunsch et al. [1994] Dev. Biol. 165:585-601). Here we present immunoblot and immunoprecipitation data showing that the JB3 antigen is secreted into tissue culture medium by day 10 chicken embryonic fibroblasts, from which it can be harvested using JB3-immunoaffinity chromatography. A single polypeptide (Mr = 350,000), which was not immunoreactive with an antibody to fibrillin-1, eluted from the affinity column. Mass spectroscopy peptide microsequencing determined the identity of the JB3 antigen to be an avian homologue of fibrillin-2. Live, whole-mounted, quail embryos were immunolabeled using a novel microinjection approach, and subsequently fixed. Laser scanning confocal microscopy indicated an elaborate scaffold of fibrillin-2 filaments encasing formed somites. At more caudal axial positions, discrete, punctate foci of immunofluorescent fibrillin-2 were observed; this pattern corresponded to the position of segmental plate mesoderm. Between segmental plate mesoderm and fully-formed somites, progressively longer filamentous assemblies of fibrillin-2 were observed, suggesting a developmental progression of fibrillin-2 fibril assembly across the somite-forming region of avian embryos. Extensive filaments of fibrillin-2 connect somites to the notochord. Similarly, fibrillin-2 connects the mesoderm associated with the anterior intestinal portal to the midline. Thus, fibrillin-2 fibrils are organized by a diverse group of cells of mesodermal or mesodermally derived mesenchymal origin. Fibrillin-2 microfilaments are assembled in a temporal and spatial pattern that is coincident with cranial-to-caudal segmentation, and regression of the anterior intestinal portal. Fibrillin-2 may function to impart physical stability to embryonic tissues during morphogenesis of the basic vertebrate body plan.

Familial occurrence of typical and severe lethal congenital contractural arachnodactyly caused by missplicing of exon 34 of fibrillin-2

Genetic linkage studies have linked congenital contractural arachnodactyly (CCA), a usually mild heritable connective-tissue disorder, to FBN2, the fibrillin gene on chromosome 5. Recently, FBN2 mutations in two patients with CCA have been described. Here we report an A-->T transversion at the -2 position of the consensus acceptor splice site, resulting in the missplicing of exon 34, a calcium-binding epidermal growth factor-like repeat in fibrillin-2 in a mother and daughter with CCA. Significantly, the mother exhibited a classic CCA phenotype with arachnodactyly, joint contractures, and abnormal pinnae, whereas her daughter exhibited a markedly more severe CCA phenotype, which included cardiovascular and gastrointestinal anomalies that led to death in infancy. Analysis of cloned fibroblasts showed that the mother is a somatic mosaic for the exon 34 missplicing mutation, whereas all the daughter's cells harbored the mutation.