A FBN1 mutation association with different phenotypes of Marfan syndrome in a Chinese family

Causative role of a novel intronic indel variant in FBN1 and maternal germinal mosaicism in Marfan syndrome

BACKGROUND

Marfan syndrome (MFS) is an autosomal dominant connective tissue disease with wide clinical heterogeneity, and mainly caused by pathogenic variants in fibrillin-1 (FBN1).

METHODS

A Chinese 4-generation MFS pedigree with 16 family members was recruited and exome sequencing (ES) was performed in the proband. Transcript analysis (patient RNA and minigene assays) and in silico structural analysis were used to determine the pathogenicity of the variant. In addition, germline mosaicism in family member (Ι:1) was assessed using quantitative fluorescent polymerase chain reaction (QF-PCR) and short tandem repeat PCR (STR) analyses.

RESULTS

Two cis-compound benign intronic variants of FBN1 (c.3464-4 A > G and c.3464-5G > A) were identified in the proband by ES. As a compound variant, c.3464-5_3464-4delGAinsAG was found to be pathogenic and co-segregated with MFS. RNA studies indicated that aberrant transcripts were found only in patients and mutant-type clones. The variant c.3464-5_3464-4delGAinsAG caused erroneous integration of a 3 bp sequence into intron 28 and resulted in the insertion of one amino acid in the protein sequence (p.Ile1154_Asp1155insAla). Structural analyses suggested that p.Ile1154_Asp1155insAla affected the protein's secondary structure by interfering with one disulfide bond between Cys1140 and Cys1153 and causing the extension of an anti-parallel β sheet in the calcium-binding epidermal growth factor-like (cbEGF)13 domain. In addition, the asymptomatic family member Ι:1 was deduced to be a gonadal mosaic as assessed by inconsistent results of sequencing and STR analysis.

CONCLUSIONS

To our knowledge, FBN1 c.3464-5_3464-4delGAinsAG is the first identified pathogenic intronic indel variant affecting non-canonical splice sites in this gene. Our study reinforces the importance of assessing the pathogenic role of intronic variants at the mRNA level, with structural analysis, and the occurrence of mosaicism.

Clinical and genetic findings in Chinese families with congenital ectopia lentis

BACKGROUND

Congenital ectopia lentis (EL) refers to the congenital dysplasia or weakness of the lens suspensory ligament, resulting in an abnormal position of the crystalline lens, which can appear as isolated EL or as an ocular manifestation of a syndrome, such as the Marfan syndrome. The fibrillin-1 protein encoded by the FBN1 gene is an essential component of the lens zonules. Mutations in FBN1 are the leading causes of congenital EL and Marfan syndrome. Owing to the complexity and individual heterogeneity of FBN1 gene mutations, the correlation between FBN1 mutation characteristics and various clinical phenotypes remains unclear.

METHODS

This study describes the clinical characteristics and identifies possible causative genes in eight families with Marfan syndrome or isolated EL using Sanger and whole-exome sequencing.

RESULTS

Eight FBN1 mutations were identified in these families, of which three (c.5065G > C, c.1600 T > A, and c.2210G > C) are reported for the first time. Based on in silico analyses, we hypothesized that these mutations may be pathogenic by affecting the fibrillin-1 protein structure and function.

CONCLUSION

These findings expand the number of known mutations involved in EL and provide a reference for the research on their genotype and phenotype associations.

Exome Sequencing Identifies Genetic Variants Associated with Extreme Manifestations of the Cardiovascular Phenotype in Marfan Syndrome

Marfan Syndrome (MFS) is an autosomal dominant condition caused by variants in the fibrillin-1 (FBN1) gene. Cardinal features of MFS include ectopia lentis (EL), musculoskeletal features and aortic root aneurysm and dissection. Although dissection of the ascending aorta is the main cause of mortality in MFS, the clinical course differs considerably in age of onset and severity, even among individuals who share the same causative variant, suggesting the existence of additional genetic variants that modify the severity of the cardiovascular phenotype in MFS. We recruited MFS patients and classified them into severe (n = 8) or mild aortic phenotype (n = 14) according to age of presentation of the first aorta-related incident. We used Exome Sequencing to identify the genetic variants associated with the severity of aortic manifestations and we performed linkage analysis where suitable. We found five genes associated with severe aortic phenotype and three genes that could be protective for this phenotype in MFS. These genes regulate components of the extracellular matrix, TGFβ pathway and other signaling pathways that are involved in the maintenance of the ECM or angiogenesis. Further studies will be required to understand the functional effect of these variants and explore novel, personalized risk management and, potentially, therapies for these patients.

Long-term outcomes after aortic root replacement for patients with Marfan syndrome

Background

A diversity of surgical strategies are used to treat Marfan syndrome patients with aortic disease. We sought to evaluate the long-term efficiency of aortic root replacement (ARR) for patients with Marfan syndrome.

Methods

Data were collected from 131 patients with Marfan syndrome and aortic disease who underwent ARR in our center. We retrospectively analyzed the long-term outcomes of these patients, among whom 68 had been diagnosed with aortic aneurysm (AA) and had undergone ARR. The remaining 63 patients had aortic dissection (AD); of these, 35 underwent ARR for limited ascending AD, while the others underwent ARR and total arch replacement combined with frozen elephant trunk (FET). Risk factors for survival and reoperation were identified.

Results

The operative mortality rate was 4.58%. Age >40 years was the sole risk factor for operative mortality. During follow-up, 12 deaths occurred. Patients aged <25 years and female patients were more prone to late death than were other patients. Indications for reoperation were noted in 22 patients, and the risk factors were age <30 years and female sex. At 5 years, the survival rate was 92.96%, and the freedom from reoperation rate was 88.36%. At 10 years, the survival rate was 85.25%, and the freedom from reoperation rate was 71.75%. The survival and freedom from reoperation rates were significantly higher in patients with AD than in those with AA. Specifically, chronic AD was a greater risk factor for late survival than was acute AD in patients with Marfan syndrome.

Conclusions

For patients with Marfan syndrome and aortic disease, ARR can be safely performed and results in low operative mortality and favorable long-term survival. Young and female patients have a higher risk for late death and reoperation. To prevent AD, surgical intervention should be promptly implemented following the diagnosis of aortic sinus dilation.

The Role of Inflammation and Myeloperoxidase-Related Oxidative Stress in the Pathogenesis of Genetically Triggered Thoracic Aortic Aneurysms

Genetically triggered thoracic aortic aneurysms (TAAs) are usually considered to exhibit minimal levels of inflammation. However, emerging data demonstrate that specific features of an inflammatory response can be observed in TAA, and that the extent of the inflammatory response can be correlated with the severity, in both mouse models and in human studies. Myeloperoxidase (MPO) is a key mediator of the inflammatory response, via production of specific oxidative species, e.g., the hypohalous acids. Specific tissue modifications, mediated by hypohalous acids, have been documented in multiple cardiovascular pathologies, including atherosclerosis associated with coronary artery disease, abdominal aortic, and cerebral aneurysms. Similarly, data are now emerging that show the capacity of MPO-derived oxidative species to regulate mechanisms important in TAA pathogenesis, including alterations in extracellular matrix homeostasis, activation of matrix metalloproteinases, induction of endothelial dysfunction and vascular smooth muscle cell phenotypic switching, and activation of ERK1/2 signaling. The weight of evidence supports a role for inflammation in exacerbating the severity of TAA progression, expanding our understanding of the pathogenesis of TAA, identifying potential biomarkers for early detection of TAA, monitoring severity and progression, and for defining potential novel therapeutic targets.

Two Novel Pathogenic FBN1 Variations and Their Phenotypic Relationship of Marfan Syndrome

Marfan syndrome is an autosomal dominant disease affecting connective tissue involving the ocular, skeletal systems with a prevalence of 1/5,000 to 1/10,000 cases. Especially cardiovascular system disorders (aortic root dilatation and enlargement of the pulmonary artery) may be life-threatening. We report here the genetic analysis results of three unrelated cases clinically diagnosed as Marfan syndrome. Deoxyribonucleic acid (DNA) was isolated from EDTA (ethylenediaminetetraacetic acid)-blood samples of the patients. A next-generation sequencing panel containing 15 genes including FBN1 was used to determine the underlying pathogenic variants of Marfan syndrome. Three different variations, NM_000138.4( FBN1 ):c.229G > A(p.Gly77Arg), NM_000138.4( FBN1 ):c.165–2A > G (novel), NM_000138.4( FBN1 ):c.399delC (p.Cys134ValfsTer8) (novel) were determined in our three cases referred with a prediagnosis of Marfan syndrome. Our study has confirmed the utility of molecular testing in Marfan syndrome to support clinical diagnosis. With an accurate diagnosis and genetic counseling for prognosis of patients and family testing, the prenatal diagnosis will be possible.

Mutation analysis of FBN1 gene in two Chinese families with congenital ectopia lentis in northern China

AIM

To summarize the phenotypes and identify the underlying genetic cause of the fibrillin-1 (FBN1) gene responsible for congenital ectopia lentis (EL) in two Chinese families in northern China.

METHODS

A detailed family history and clinical data from all participants were collected by clinical examination. The candidate genes were captured and sequenced by targeted next-generation sequencing, and the results were confirmed by Sanger sequencing. Haplotyping was used to confirm the mutation sequence. Real-time PCR was used to determine the FBN1 messenger ribonucleic acid (mRNA) levels in patients with EL and in unaffected family members.

RESULTS

The probands and other patients in the two families were affected with congenital isolated EL. A heterozygous FBN1 mutation in exon 21 (c.2420_IVS20-8 delTCTGAAACAinsCGAAAG) was identified in FAMILY-1. A heterozygous FBN1 mutation in exon 14 (c.1633C>T, p.R545C) was identified in FAMILY-2. Each mutation co-segregated with the affected individuals in the family and did not exist in unaffected family members and 200 unrelated normal controls.

CONCLUSION

The insertion-deletion mutation (c.2420 IVS20-8delTCTGAAACA insCGAAAG) in the FBN1 gene is first identified in isolated EL. The mutation (c.1633C>T) in the FBN1 gene was a known mutation in EL patient. The variable phenotypes among the patients expand the phenotypic spectrum of EL in a different ethnic background.

Stickler syndrome: exploring prophylaxis for retinal detachment

PURPOSE OF REVIEW

The literature regarding prophylactic treatment of rhegmatogenous retinal detachment in Stickler syndrome remains controversial. We review major published clinical studies and offer a critical analysis of this subject.

SUMMARY

Stickler syndrome is a systemic collagenopathy affecting multiple organ systems including the eye, ear, and skeleton. Stickler syndrome is probably the most common cause of genetically determined pediatric rhegmatogenous retinal detachment. Congenital developmental anomalies constitute over half rhegmatogenous detachments (RRD) in patients less than 10 years. The majority are caused by hereditary vitreoretinopathies associated with Stickler syndrome. Sixty percent of patients with Stickler syndrome develop RRD's over their lifetime with possible severe visual loss and subsequent lifelong morbidity. In view of these complications, some have emphasized the importance of prophylactic laser treatment to the retina of patients with Stickler syndrome to reduce the occurrence of and/or prevent future rhegmatogenous retinal detachment, but there appears to be insufficient data to support the absolute benefit of such prophylactic treatment. Guidelines regarding the age at prophylactic treatment as well as type and frequency of intervention are scarce and would benefit from additional clinical investigations.

Epigenetic influences on genetically triggered thoracic aortic aneurysm

Genetically triggered thoracic aortic aneurysms (TAAs) account for 30% of all TAAs and can result in early morbidity and mortality in affected individuals. Epigenetic factors are now recognised to influence the phenotype of many genetically triggered conditions and have become an area of interest because of the potential for therapeutic manipulation. Major epigenetic modulators include DNA methylation, histone modification and non-coding RNA. This review examines epigenetic modulators that have been significantly associated with genetically triggered TAAs and their potential utility for translation to clinical practice.

A novel FBN2 mutation cosegregates with congenital contractural arachnodactyly in a five-generation Chinese family

We identified a novel heterozygous mutation (c.4177T>G and p.Cys1393Gly) in FBN2 that cosegregated with congenital contractural arachnodactyly (CCA) in a five-generation Chinese family. This mutation may cause the loss of the disulfide bond between Cys 1393 and Cys 1378 residues of fibrillin-2. Our study expands the genetic profile of CCA.