Application of next-generation sequencing to screen for pathogenic mutations in 123 unrelated Chinese patients with Marfan syndrome or a related disease.

Marfan syndrome (MFS) is a systemic connective tissue disease principally affecting the ocular, skeletal and cardiovascular systems. This autosomal dominant disorder carries a prevalence of 1:3,000 to 1:5,000. This study aims to define the mutational spectrum of MFS related genes in Chinese patients and to establish genotype-phenotype correlations in MFS. Panel-based targeted next-generation sequencing was used to analyze the FBN1, TGFBR1 and TGFBR2 genes in 123 unrelated Chinese individuals with MFS or a related disease. Genotype-phenotype correlation analyses were performed in mutation-positive patients. The results showed that 97 cases/families (78.9%; 97/123) harbor at least one (likely) pathogenic mutation, most of which were in FBN1; four patients had TGFBR1/2 mutations; and one patient harbored a SMAD3 mutation. Three patients had two FBN1 mutations, and all patients showed classical MFS phenotypes. Patients with a dominant negative-FBN1 mutation had a higher prevalence of ectopia lentis (EL). Patients carrying a haploinsufficiency-FBN1 mutation tended to have aortic dissection without EL. This study extends the spectrum of genetic backgrounds of MFS and enriches our knowledge of genotype-phenotype correlations.

Tailoring the American College of Medical Genetics and Genomics and the Association for Molecular Pathology Guidelines for the Interpretation of Sequenced Variants in the FBN1 Gene for Marfan Syndrome: Proposal for a Disease- and Gene-Specific Guideline.

BACKGROUND: The introduction of next-generation sequencing techniques has substantially increased the identification of new genetic variants and hence the necessity of accurate variant interpretation. In 2015, the American College of Medical Genetics and Genomics and the Association for Molecular Pathology proposed new variant interpretation guidelines. Gene-specific characteristics were, however, not considered, sometimes leading to inconsistent variant interpretation. METHODS: To allow a more uniform interpretation of variants in the FBN1 (fibrillin-1) gene, causing Marfan syndrome, we tailored these guidelines to this gene and disease. We adapted 15 of the 28 general criteria and classified 713 FBN1 variants previously identified in our laboratory as causal mutation or variant of uncertain significance according to these adapted guidelines. We then compared the agreement between previous methods and the adapted American College of Medical Genetics and Genomics and the Association for Molecular Pathology criteria. RESULTS: Agreement between the methods was 86.4% (K-alpha, 0.6). Application of the tailored guidelines resulted in an increased number of variants of uncertain significance (14.5% to 24.2%). Of the 85 variants that were downscaled to likely benign or variant of uncertain significance, 59.7% were missense variants outside a well-established functional site. Available clinical- or segregation data, necessary to further classify these types of variants, were in many cases insufficient to aid the classification. CONCLUSIONS: Our study shows that classification of variants remains challenging and may change over time. Currently, a higher level of evidence is necessary to classify a variant as pathogenic. Gene-specific guidelines may be useful to allow a more precise and uniform interpretation of the variants to accurately support clinical decision-making.

Pathogenic FBN1 mutations in 146 adults not meeting clinical diagnostic criteria for Marfan syndrome: further delineation of type 1 fibrillinopathies and focus on patients with an isolated major criterion.

Mutations in the FBN1 gene cause Marfan syndrome (MFS) and have been associated with a wide range of milder overlapping phenotypes. A proportion of patients carrying a FBN1 mutation does not meet diagnostic criteria for MFS, and are diagnosed with "other type I fibrillinopathy." In order to better describe this entity, we analyzed a subgroup of 146 out of 689 adult propositi with incomplete "clinical" international criteria (Ghent nosology) from a large collaborative international study including 1,009 propositi with a pathogenic FBN1 mutation. We focused on patients with only one major clinical criterion, [including isolated ectopia lentis (EL; 12 patients), isolated ascending aortic dilatation (17 patients), and isolated major skeletal manifestations (1 patient)] or with no major criterion but only minor criteria in 1 or more organ systems (16 patients). At least one component of the Ghent nosology, insufficient alone to make a minor criterion, was found in the majority of patients with isolated ascending aortic dilatation and isolated EL. In patients with isolated EL, missense mutations involving a cysteine were predominant, mutations in exons 24-32 were underrepresented, and no mutations leading to a premature truncation were found. Studies of recurrent mutations and affected family members of propositi with only one major clinical criterion argue for a clinical continuum between such phenotypes and classical MFS. Using strict definitions, we conclude that patients with FBN1 mutation and only one major clinical criterion or with only minor clinical criteria of one or more organ system do exist but represent only 5% of the adult cohort.

Prevalence of dural ectasia in 63 gene-mutation-positive patients with features of Marfan syndrome type 1 and Loeys-Dietz syndrome and report of 22 novel FBN1 mutations.

Marfan syndrome is an autosomal dominant disorder involving different organ systems. Marfan syndrome type 1 (MFS1) is caused by mutations in the FBN1 gene. Heterozygosity for mutations in the TGFBR1 or TGFBR2 genes cause Loeys-Dietz syndrome (LDS) types 2A and 2B that overlap with MFS1 in their clinical features. The phenotype of MFS1 is defined by the Ghent nosology, which classifies the clinical manifestations in major and minor criteria. Dural ectasia is one of the major criteria for Marfan syndrome but it is rarely tested for. We here report 22 novel and 9 recurrent mutations in the FBN1 gene in 36 patients with clinical features of Marfan syndrome. Sixty patients with identified mutations in the FBN1 gene and three patients with mutations in the TGFBR1 or TGFBR2 genes were examined for dural ectasia. Forty-seven of the 60 patients (78%) with MFS1 showed the dural ectasia criterion and 13 (22%) did not. Thirty-three (55%) patients were suspected of having Marfan syndrome and 24 (73%) of them had dural ectasia. Two of the three patients with LDS had dural ectasia.

A Japanese family of typical Loeys-Dietz syndrome with a TGFBR2 mutation.

This report describes a Japanese family with vessel and craniofacial abnormalities. Although the clinical findings of the patient's father fulfilled the diagnostic criteria for Marfan syndrome, arterial tortuosity, aneurysms, hypertelorism and a bifid uvula were noted in both the patient and his father. These findings were compatible with the clinical manifestations that were previously reported in Loeys-Dietz syndrome. A molecular genetic analysis demonstrated a heterozygous missense mutation of the transforming growth factor-beta receptor II gene in both the patient and his father, which thus caused Loeys-Dietz syndrome. This is the first Japanese family case report of typical Loeys-Dietz syndrome.

The importance of mutation detection in Marfan syndrome and Marfan-related disorders: report of 193 FBN1 mutations.

Mutations in the FBN1 gene have been characterised in patients affected by Marfan syndrome and Marfan-related disorders. Starting with genomic DNA, we analysed the FBN1 gene using PCR, SSCP and/or dHPLC analysis, and automatic sequencing of abnormal bands/peaks, in a consecutive series of 508 patients, of which 22 were children less than 5 years old. Our results are comparable with those reported by other groups. In this study we observed 193 mutations, 126 of which previously unreported. A total of 331 relatives (including 51 infants) of 120 probands for whom a family mutation had been identified here or elsewhere, were tested for the presence of that particular mutation. In addition, 4 prenatal tests were carried out. The identification of a mutation allows for early diagnosis, prognosis, genetic counselling, preventive management of carriers and reassurance for unaffected relatives. The importance of knowing in advance the location of the putative family mutation is highlighted by its straightforward application to prenatal and postnatal screening.

Heritable disorders of connective tissue.

This chapter seeks to draw readers' attention to the importance of the heritable disorders of connective tissue in clinical practice. It describes the principal features of the Marfan and Ehlers-Danlos syndromes, osteogenesis imperfecta and benign joint hypermobility syndrome, their clinical and prognostic similarities and differences, and their distinguishing features. Recently revised international classifications drawing on advances in molecular genetics are described in detail. Wherever possible, patients' symptoms are explained on the basis of the altered biomechanics of genetically aberrant connective tissue matrix proteins. Finally, the chapter draws attention to the often unrecognized burden of chronic pain borne by patients with these conditions, a feature of which many rheumatologists seem unaware, and sets out a rational and holistic approach to treatment and management that is based on the best currently available evidence.

Joint hypermobility and genetic collagen disorders: are they related?

The HDCTs constitute a heterogeneous group of rare genetically determined diseases, the best known of which are Ehlers-Danlos and Marfan syndromes and osteogenesis imperfecta. Hypermobility is a feature common to them all, but it is also a feature that is highly prevalent in the population at large. Symptomatic hypermobile subjects (whose symptoms are attributable to their hypermobility) are said to be suffering from the benign joint hypermobility syndrome, which has many features that overlap with the HDCTs. It is not yet known whether there is a variety of hypermobility (symptomatic or otherwise) that is not part of a connective tissue disorder.

Life expectancy in British Marfan syndrome populations.

A total of 206 patients with Marfan syndrome were ascertained throughout genetic clinics in Wales and Scotland during the period 1970-1990. There were 45 deaths representing 22% of the cohort. Mean age at death was 45.3+/-16.5 years. 50% median cumulative survival in the total cohort (n=206) was 53 years for males and 72 years for females. Multivariate analysis confirmed severity as the best independent indicator of survival. These findings and survival curves will assist in the counselling of British families and individuals with Marfan syndrome.

Abnormal morphology of fibrillin microfibrils in fibroblast cultures from patients with neonatal Marfan syndrome.

The Marfan syndrome (MFS) is a connective tissue disorder manifested by variable and pleiotropic features in the skeletal, ocular, and cardiovascular systems. The average life span in MFS is about 35 years. A group with much more severe cardiovascular disease and a mean life span of approximately 1 year also exists. We refer to this latter group as "neonatal Marfan syndrome" (nMFS). Fibrillin defects are now known to be the cause of MFS and nMFS. Immunofluorescence studies were the first to demonstrate this association. Here we describe immunofluorescence studies in a series of 10 neonates and summarize their salient clinical features. In vitro accumulation of fibrillin reactive fibers was assayed using monoclonal antibodies to fibrillin in hyperconfluent fibroblast cultures. As was previously observed in MFS, fibroblast cultures from nMFS patients showed an apparent decrease in accumulation of immunostainable fibrillin. Significantly, however, the morphology of the immunostained fibrils in the nMFS cultures were abnormal and differed not only from control cultures, but also from those seen in cultures of MFS fibroblasts. The nMFS fibrils appeared short, fragmented, and frayed, characteristics that are not seen in MFS. Both the clinical and fibrillin morphology data provide evidence to suggest a useful subclassification of nMFS in the spectrum of MFS.

A second locus for Marfan syndrome maps to chromosome 3p24.2-p25.

Marfan syndrome (MFS) is an autosomal dominant connective-tissue disorder characterized by skeletal, ocular and cardiovascular defects of highly variable expressivity. The diagnosis relies solely on clinical criteria requiring anomalies in at least two systems. By excluding the chromosome 15 disease locus, fibrillin 1 (FBN1), in a large French family with typical cardiovascular and skeletal anomalies, we raised the issue of genetic heterogeneity in MFS and the implication of a second locus (MFS2). Linkage analyses, performed in this family, have localized MFS2 to a region of 9 centiMorgans between D3S1293 and D3S1283, at 3p24.2-p25. In this region, the highest lod score was found with D3S2336, of 4.89 (theta = 0.05). By LINKMAP analyses, the most probable position for the second locus in MFS was at D3S2335.

Orthopedic aspects of the Marfan phenotype.

Thirty-six patients with the phenotypic features of Marfan's syndrome (arachnodactyly, abnormal ratio of arm span to height, ligamentous laxity, and tall stature) were evaluated and classified into three groups. Group 1 represented definite Marfan's syndrome and included patients with two or more major signs, with additional minor signs as described by McKusick (18 patients). Group 2 represented probable Marfan's syndrome and included patients with one major sign and multiple minor signs (nine patients). Group 3 represented the Marfan phenotype and included patients with multiple minor signs (nine patients). A high incidence of scoliosis occurred in all groups (100% in Group 1 and 89% in Groups 2 and 3 combined). Group 1 patients had longer, multiple, and more progressive spinal curves. Protrusio acetabuli (Type II and III hips) was present in 22 patients (11 in Group 1, six in Group 2, and five in Group 3), with more severe involvement noted in Group 1. Foot deformities of varying types and severity occurred in all groups but were seen most often in Group 1 patients. Patients with the features of Marfan's syndrome (even without major diagnostic criteria) have a high incidence of progressive scoliosis, protrusio acetabuli, and foot deformities.

Beals syndrome: clinical and molecular investigations in a kindred of Indian descent.

Eight members of a 3-generation kindred of Indian descent with congenital contractural arachnodactyly (Beals syndrome) have been appraised. Considerable variation was noted in the clinical features of affected persons, and the previously unreported associated finding of clubbing of the fingers and toes was evident in two individuals. The family was investigated using conventional serum and protein markers, and RFLP probes for type I and II collagen. No linkage in affected members could be demonstrated with type I collagen probes.

Marfanoid children. Etiologic heterogeneity and cardiac findings.

The clinical, cardiac, and echocardiographic test results of 20 children with marfanoid features are reviewed. Fifteen were diagnosed as having Marfan syndrome, two had "possible" Marfan syndrome, and three had other diagnoses. On first evaluation, eight patients with Marfan syndrome (53%) had mitral regurgitation and none had aortic regurgitation. Echocardiography showed aortic root enlargement in 12 (80%) of 15 patients and mitral valve prolapse in 12 (80%) of 15. None had a normal echocardiogram. At follow-up examination, one patient had developed aortic root enlargement, and one patient, mitral valve prolapse. Thus, although aortic root enlargement is usually present in early childhood in patients with Marfan syndrome, it is not considered specific because in this study it also occurred in one child with Alport's syndrome and in one with marfanoid features. Four patients with aortic root enlargement were treated with propranolol and their echocardiograms showed no further increase in the aortic root diameter for several years. We recommend echocardiography in the diagnosis and routine management of children in whom Marfan syndrome is suspected.

Contractural arachnodactyly with mitral regurgitation and iridodonesis.

An infant girl with arachnodactyly, spontaneously resolving contractures, dolichostenomelia, iridodonesis, and mitral and tricuspid incompetence died in cardiac failure. We confirm that congenital contractural arachnodactyly may exhibit serious cardiovascular and ophthalmic complications like Marfan's syndrome. The presence of iridodonesis further obscures the differentiation between classical Marfan's syndrome and congenital contractural arachnodactyly.