Clinical utility gene card for: Marfan syndrome type 1 and related phenotypes [FBN1]

FBN1 gene mutations in 26 Hungarian patients with suspected Marfan syndrome or related fibrillinopathies

Marfan syndrome (MFS) is an autosomal dominant connective tissue disorder mainly affecting the cardiovascular, ocular and musculo-skeletal systems. FBN1 gene mutations lead to MFS and related connective tissue disorders. In this work we described clinical and molecular data of 26 unrelated individuals with suspected MFS who were referred for FBN1 mutation analysis. FBN1 gene sequencing was performed by next generation sequencing and Sanger sequencing methods. We identified 23 causal or potentially causal (including variants of uncertain significance) FBN1 variants, seven of them was novel (˜30%). About 30% of the cases were sporadic. FBN1 mutations were associated with MFS in the majority of the patients, in two cases with severe and early onset manifestation of the syndrome. Missense mutations were detected in 69.6% (16/23), the majority of them were located in one of the cbEGF motifs and ˜70% of them substituted conserved cystein residues. Small deletions/duplications were identified in 13% of the cases (3/23), while splice site variants were detected in 17.4% (4/23). In three unrelated patients a low frequency recurrent silent variant (c.3294C > T (p.Asp1098=) was identified. FBN1 mRNA analysis showed that the mutation does not lead to aberrant splicing, based on available data the mutation was classified as benign.

A Novel Heterozygous Intronic Mutation in the FBN1 Gene Contributes to FBN1 RNA Missplicing Events in the Marfan Syndrome

Marfan syndrome (MFS) is an autosomal dominantly inherited connective tissue disorder, mostly caused by mutations in the fibrillin-1 (FBN1) gene. We, by using targeted next-generation sequence analysis, identified a novel intronic FBN1 mutation (the c.2678-15C>A variant) in a MFS patient with aortic dilatation. The computational predictions showed that the heterozygous c.2678-15C>A intronic variant might influence the splicing process by differentially affecting canonical versus cryptic splice site utilization within intron 22 of the FBN1 gene. RT-PCR and Western blot analyses, using FBN1 minigenes transfected into HeLa and COS-7 cells, revealed that the c.2678-15C>A variant disrupts normal splicing of intron 22 leading to aberrant 13-nt intron 22 inclusion, frameshift, and premature termination codon. Collectively, the results strongly suggest that the c.2678-15C>A variant could lead to haploinsufficiency of the FBN1 functional protein and structural connective tissue fragility in MFS complicated by aorta dilation, a finding that further expands on the genetic basis of aortic pathology.

Non-cardiac manifestations of Marfan syndrome

Because of the widespread distribution of fibrillin 1 in the body, Marfan syndrome (MFS) affects virtually every system. The expression of this single dominantly inherited gene is variable within a family, and between families. There is some genotype-phenotype correlation which is helpful in guiding long-term prognosis, and management. In general gene mutations have been reported in clusters, with those having mainly ocular manifestations occurring in exons 1 to 15 of this 65-exon gene; those causing cardiac problems often involving cysteine replacement in a calcium binding EGF-like sequence; the most severe mutations occurring in exons 25-32, causing neonatal MFS diagnosed at birth, and severe enough to cause death frequently before the age of 2. Other correlations will certainly be found in future. This condition is progressive, and the manifestations unfold according to age. For example, if the lens is going to dislocate this usually occurs by age 10; scoliosis usually presents itself between the ages of 8 and 15; height should be monitored carefully between the onset of puberty and cessation of growth approximately age 17 or 18. Holistic care should be offered by one doctor who oversees the patient's welfare. This should be a paediatrician, paediatric cardiologist, or general practitioner in the case of an affected child. Thereafter, the physician in charge of the most seriously affected system should be aware that other systems need to be managed through a referral network.

Athletes and the Aorta: Normal Adaptations and the Diagnosis and Management of Pathology

OPINION STATEMENT

Over a hundred years ago, physicians first recognized that participation in regular, vigorous training resulted in enlargement of the heart. Since that time, the term "athlete's heart" has entered the medical lexicon as a global expression encompassing the electrical, functional, and morphological adaptations that develop in response to physical training. Exercise-induced adaptations of the aorta, which is also exposed to large hemodynamic stresses during prolonged endurance exercise or resistance training, are less well recognized. Young athletes tend to have slightly larger aortas than their sedentary counterparts; however, this rarely exceeds normal ranges for the general population. A systematic approach is advised when presented with an athlete with aortic enlargement. The size of the aorta needs to be first put in the context of the athlete's age, sex, size, and sporting endeavors; however, even in the largest young athletes, the aortic root rarely exceeds 4 cm in men or 3.4 cm in women. A comprehensive evaluation is advised which includes a detailed family history and a thorough physical examination evaluating for signs of any defined connective tissue disorder associated with aortopathy. Downstream testing is then tailored for the individual and may include further tomographic imaging, opthalmology review, and genetic testing. This should ideally be performed at a specialist center. Management of athletes with an aortopathy includes tailoring athletic activity, medical management with strict impulse control, and, in some cases, prophylactic surgery. The issue of sporting eligibility should be individualized and if disqualification is necessary, this should be undertaken by a sports cardiologist or an expert in aortic disease with experience in dealing with an athletic population.

De Novo Paternal FBN1 Mutation Detected in Embryos Before Implantation

Background

Marfan syndrome (MFS) is an autosomal dominant disease caused by mutations in the Fibrillin (FBN)1 gene and characterized by disorders in the cardiovascular, skeletal, and visual systems. The diversity of mutations and phenotypic heterogeneity of MFS make prenatal molecular diagnoses difficult. In this study, we used pre-implantation genetic diagnosis (PGD) to identify the pathogenic mutation in a male patient with MFS and to determine whether his offspring would be free of the disease.

Material/Methods

The history and pedigree of the proband were analyzed. Mutation analysis was performed on the couple and immediate family members. The couple chose IVF treatment and 4 blastocysts were biopsied. PGD was carried out by targeted high-throughput sequencing of the FBN1 gene in the embryos, along with single-nucleotide polymorphism haplotyping. Sanger sequencing was used to confirm the causative mutation.

Results

c.2647T>C (p.Trp883Arg) was identified as the de novo likely pathogenic mutation in the proband. Whole-genome amplification and sequencing of the 3 embryos revealed that they did not carry the mutation, and 1 blastocyst was transferred back to the uterus. The amniocentesis test result analyzed by Sanger sequencing confirmed the PGD. A premature but healthy infant free of heart malformations was born.

Conclusions

The de novo mutation c.2647T>C (p.Trp883Arg) in FBN1 was identified in a Chinese patient with MFS. Embryos without the mutation were identified by PGD and resulted in a successful pregnancy.

Genetic testing of 248 Chinese aortopathy patients using a panel assay

Inherited aortopathy, which is characterized by a high risk of fatal aortic aneurysms/dissections, can occur secondarily to several syndromes. To identify genetic mutations and help make a precise diagnosis, we designed a gene panel containing 15 genes responsible for inherited aortopathy and tested 248 probands with aortic disease or Marfan syndrome. The results showed that 92 individuals (37.1%) tested positive for a (likely) pathogenic mutation, most of which were FBN1 mutations. We found that patients with a FBN1 truncating or splicing mutation were more prone to developing severe aortic disease or valvular disease. To date, this is the largest reported cohort of Chinese patients with aortic disease who have undergone genetic testing. Therefore, it can serve as a considerable dataset of next generation sequencing data analysis of Chinese population with inherited aortopathy. Additionally, according to the accumulated data, we optimized the analysis pipeline by adding quality control steps and lowering the false positive rate.

Genetic testing in Marfan syndrome

Genetic testing is aiding rapid diagnosis of Marfan syndrome as a basis for management of eye, heart and skeletal disease. The affected patient's mutation can be used as a basis for prenatal or postnatal diagnosis of offspring. Preimplantation genetic diagnosis, the technique of choice, can ensure an unaffected pregnancy.

Plan of Action for Inherited Cardiovascular Diseases: Synthesis of Recommendations and Action Algorithms

The term inherited cardiovascular disease encompasses a group of cardiovascular diseases (cardiomyopathies, channelopathies, certain aortic diseases, and other syndromes) with a number of common characteristics: they have a genetic basis, a familial presentation, a heterogeneous clinical course, and, finally, can all be associated with sudden cardiac death. The present document summarizes some important concepts related to recent advances in sequencing techniques and understanding of the genetic bases of these diseases. We propose diagnostic algorithms and clinical practice recommendations and discuss controversial aspects of current clinical interest. We highlight the role of multidisciplinary referral units in the diagnosis and treatment of these conditions.

Design and rationale of a prospective, collaborative meta-analysis of all randomized controlled trials of angiotensin receptor antagonists in Marfan syndrome, based on individual patient data: A report from the Marfan Treatment Trialists' Collaboration

Rationale

A number of randomized trials are underway, which will address the effects of angiotensin receptor blockers (ARBs) on aortic root enlargement and a range of other end points in patients with Marfan syndrome. If individual participant data from these trials were to be combined, a meta-analysis of the resulting data, totaling approximately 2,300 patients, would allow estimation across a number of trials of the treatment effects both of ARB therapy and of β-blockade.

Such an analysis would also allow estimation of treatment effects in particular subgroups of patients on a range of end points of interest and would allow a more powerful estimate of the effects of these treatments on a composite end point of several clinical outcomes than would be available from any individual trial.

Design

A prospective, collaborative meta-analysis based on individual patient data from all randomized trials in Marfan syndrome of (i) ARBs versus placebo (or open-label control) and (ii) ARBs versus β-blockers will be performed.

A prospective study design, in which the principal hypotheses, trial eligibility criteria, analyses, and methods are specified in advance of the unblinding of the component trials, will help to limit bias owing to data-dependent emphasis on the results of particular trials. The use of individual patient data will allow for analysis of the effects of ARBs in particular patient subgroups and for time-to-event analysis for clinical outcomes.

The meta-analysis protocol summarized in this report was written on behalf of the Marfan Treatment Trialists' Collaboration and finalized in late 2012, without foreknowledge of the results of any component trial, and will be made available online (http://www.ctsu.ox.ac.uk/research/meta-trials).

Current and future pharmacological treatment strategies with regard to aortic disease in Marfan syndrome

INTRODUCTION

Marfan syndrome is a multisystemic connective tissue disorder caused mainly by mutations in the fibrillin-1 gene. The entire cardiovascular system is affected in patients with Marfan syndrome. Aortic root dilatation, aortic valve regurgitation or - the most feared and life-threatening symptom - aortic root dissection are the most common manifestations. Therapeutic strategies, such as prophylactic aortic root surgery and pharmacological therapy, focus on the prevention of aortic dissection. Currently, the standard medicinal treatments targeting aortic dilatation and dissection consist of agents generally used to lower blood pressure and/or the inotropic state of the heart. By these means, the cyclic repetitive forces exerted on the aortic wall are diminished and thus the onset of aortic dilatation is potentially prevented. Although these pharmacological agents may offer some benefit in reduction of aortic aneurysm expansion rate, they do not target the underlying cause of the progressive aortic degradation.

AREAS COVERED

This review discusses the effectiveness of frequently prescribed medications used to prevent and delay aortic complications in Marfan syndrome. New insights on the biochemical pathways leading to aortic disease are also discussed to highlight new targets for pharmacological therapy.

EXPERT OPINION

Recent insights in the transforming growth factor beta signaling pathway and inflammatory mechanisms in a well-established mouse model of Marfan syndrome, have led to studies exploring new pharmacological treatment strategies with doxycycline, statins and angiotensin II receptor blockers. Pharmacological therapy is focused more on prevention than on delay of aortic wall pathology in Marfan syndrome. Of the new pharmacological treatment strategies targeting aortic pathology in Marfan syndrome, angiotensin receptor type 1 blockers are promising candidates, with several clinical trials currently ongoing.