Recurrent FBN1 mutation (R62C) in a Chinese family with isolated ectopia lentis

Rare Variants and Polymorphisms of FBN1 Gene May Increase the Risk of Non-Syndromic Aortic Dissection

Aortic dissection (AD) is a cardiovascular disease characterized by high mortality and poor prognosis. Although FBN1 is associated with syndromic AD, its association with non-syndromic AD remains unclear. In this study, DNA samples from 90 Chinese individuals with non-syndromic AD (60 Stanford A, 30 Stanford B types) were analyzed to determine the relationship between diverse genotypes of the FBN1 gene and non-syndromic AD. Eleven pathogenic/likely pathogenic variants (1 novel) were identified in 12.2% of patients with non-syndromic AD. Patients with positive variants suffered from AD at a younger age than those in the negative variant group. Among the six positive missense mutations associated with cysteine residue hosts, four (66.7%) were Stanford A AD, whereas two (33.3%) were Stanford B AD. Three (100%) positive splicing/truncation variant hosts were Stanford A AD. The splicing/truncation variants and missense variants involving cysteine residues in the FBN1 gene increased the risk of Stanford A AD. Ten common SNPs that increased susceptibility to AD were identified. In particular, five SNPs were detected significantly in Stanford A AD, whereas another four SNPs were significantly detected in Stanford B AD. These significant variants can function as biomarkers for the identification of patients at risk for AD. Our findings have the potential to broaden the database of positive mutations and common SNPs of FBN1 in non-syndromic AD among the Chinese population.

Fibrillin-1 gene mutations in a Chinese cohort with congenital ectopia lentis: spectrum and genotype-phenotype analysis

AIMS

To identify the mutation spectrum and genotype-phenotype correlations of fibrillin-1 (FBN1) mutations in a Chinese cohort with congenital ectopia lentis (EL).

METHODS

Patients clinically suspected of congenital zonulopathy were screened using panel-based next-generation sequencing followed by multiplex ligation-dependent probe amplification. All the probands were subjected to thorough ocular examinations. Molecular and clinical data were integrated in pursuit of genotype-phenotype correlation.

RESULTS

A total of 131 probands of FBN1 mutations from unrelated families were recruited. Around 65% of the probands were children younger than 9 years old. Overall, 110 distinct FBN1 mutations were identified, including 39 novel ones. The most at-risk regions were exons 13, 2, 6, 15, 24 and 33 in descending order of mutation frequency. The most prevalent mutation was c.184C>T (seven, 5.34%) in the coding sequence and c.5788+5G>A (three, 2.29%) in introns. Missense mutations were the most frequent type (103, 78.63%); half of which were distributed in the N-terminal regions (53, 51.46%). The majority of missense mutations were detected in one of the calcium-binding epidermal growth factor-like domains (62, 60.19%), and 39 (62.90%) of them were substitutions of conserved cysteine residues. Microspherophakia (MSP) was found in 15 patients (11.45%). Mutations in the middle region (exons 22-42), especially exon 26, had higher risks of combined MSP (OR, 5.51 (95% CI 1.364 to 22.274), p=0.017).

CONCLUSIONS

This study extended the knowledge of the FBN1 mutation spectrum and provided novel insights into its clinical correlation regarding EL and MSP in the Chinese population.

Genotype variant screening and phenotypic analysis of FBN1 in Chinese patients with isolated ectopia lentis

Isolated ectopia lentis (IEL) can lead to blindness as result of severe complications, such as retinal detachment and secondary glaucoma. Pathogenic variants in the fibrillin 1 (FBN1) gene are a common cause of IEL. The aim of the present study was to investigate the frequency of pathogenic FBN1 variants in twelve probands with IEL and to evaluate their associated phenotypes. Systemic clinical examination of the twelve probands indicated that all had bilateral EL with a median age at diagnosis of three years. High myopia was the most common feature among the probands (83.3%; 10/12 cases). No extraocular symptoms (either cardiovascular or skeletal) were observed among these patients. Genomic DNA was extracted from peripheral blood leukocytes from all patients for targeted exome sequencing. Seven heterozygous missense variants in FBN1 were identified by bioinformatics analysis and further verified using Sanger sequencing. The seven variants were all classified as pathogenic after segregation analysis on available family members according to the American College of Medical Genetics and Genomics standards and guidelines. Of the seven variants, three were novel, namely c.2179T>C, c.2496T>G and c.3346G>C. The remaining four, namely c.184C>T, c.367T>C, c.1879C>T and c.4096G>A have been reported in previous studies. The seven pathogenic variants were identified in 8/12 (66.7%) probands with IEL. These results expand the variant spectrum of the FBN1 gene as well as the understanding of the molecular pathogenesis of IEL.

Novel p.G1344E mutation in FBN1 is associated with ectopia lentis

Background

Ectopia lentis refers to dislocation or subluxation of the crystalline lens. Fibrillin-1, encoded by FBN1, is an important microfibrillar structural component that is specifically required for the suspensory ligament of the lens. FBN1 mutations may cause abnormal structure of microfibrils and has been associated with a broad spectrum of clinical phenotypes. In this study, we characterised a Chinese dominant family with late-onset isolated ectopia lentis caused by a novel missense FBN1 mutation.

Methods

Eight family members, including four patients with suspected isolated ectopia lentis, were recruited from Shanghai. Clinical data and family history of the proband and other affected family members were collected. Ophthalmic examination, systemic examination and echocardiography were performed. Whole exome sequencing and Sanger sequencing were used to detect potential pathogenic variants.

Results

A novel heterozygous missense mutation c.4031 G>A/p.Gly1344Glu in exon 33 of FBN1 was identified. This mutation was detected in all affected family members and led to specific ocular system phenotypes (ectopia lentis, microspherophakia and secondary glaucoma) with minor skeletal involvement (hallux valgus).

Conclusion

The novel c.4031G>A mutation in FBN1 is a likely pathogenic mutation for isolated ectopia lentis. Our study expands the spectrum of FBN1 mutations and contributes to better comprehension of genotype-phenotype correlations of ectopia lentis disease.

Ophthalmic findings in a family with early-onset isolated ectopia lentis and the p.Arg62Cys mutation of the fibrillin-1 gene (FBN1)

PURPOSE

The purpose of this paper is to describe ophthalmic findings in a family with isolated ectopia lentis (EL) caused by a specific FBN1 mutation.

METHODS

Detailed family histories and clinical data were recorded for six isolated EL patients of 11 family members. The ophthalmological and systematic examinations were performed on patients and unaffected members of the investigated family. The detailed ocular examinations included visual acuity, anterior chamber depth, pupil size, lens location, optometry, central corneal thickness, keratometry, slitlamp examination, fundus examination, axial length, ocular B-ultrasound, gonioscope checking, ultrasound biomicroscopy (UBM) and intraocular pressure (IOP; Goldmann applanation tonometer). Systematic examinations included the measurement of echocardiogram, height, arm span, skull, face, jaw, tooth, breast bone, spinal column, and skin. Genomic DNA was extracted using the phenol-chloroform extraction method for all subjects, and sequencing was carried out on an ABI Prism 3730 Genetic Analyzer.

RESULTS

A heterozygous mutation, c.184C>T (p.Arg62Cys) in exon 2 of FBN1 was identified in all affected members but was not found in any unaffected member of the family. Our study presented detailed clinical manifestations, including some novel ophthalmic findings, such as pupillary abnormality, different types of glaucoma, and progressive hyperopia.

CONCLUSIONS

Ophthalmic findings and the p.Arg62Cys mutation of FBN1 gene were reported in a family with early-onset isolated ectopia lentis.

Exon 47 skipping of fibrillin-1 leads preferentially to cardiovascular defects in patients with thoracic aortic aneurysms and dissections

Excessive activation of the transforming growth factor beta signaling pathway and disorganized cellular skeleton caused by genetic mutations are known to be responsible for the inherited thoracic aortic aneurysms and dissections (TAAD), a life-threatening vascular disease. To investigate the genotype-phenotype correlation, we screened genetic mutations of fibrillin-1 (FBN1), transforming growth factor-β receptor-1 (TGFBR1) and transforming growth factor-β receptor-2 (TGFBR2) for TAAD in 7 affected families and 22 sporadic patients. Of 19 potential mutations identified in FBN1, 11 appeared novel while the others were recurrent. Two mutations were detected in TGFBR2. Eight patients carried no mutation in either of these genes. Characterization of FBN1 c.5917+6T>C in transfected HEK293 cells demonstrated that it caused skipping of exon 47, leading to the loss of the 33th calcium binding epidermal growth factor-like domain associated with Marfan syndrome. Compared with exon 46, skipping of 47 did not cause patients ectopia lentis in all carriers. To correlate genotypes with phenotypes in different human ancestries, we reviewed the published mutational studies on FBN1 and found that the probability of cardiovascular defects were significantly increased in Chinese patients with premature termination codon or splicing mutations than those with missense mutations (91.7 % vs 54.2 %, P = 0.0307) or with noncysteine-involved point mutations than those with cysteine-involved mutations (88.9 % vs 33.3 %, P = 0.0131). Thus, we conclude that exon 47 skipping of FBN1 leads preferentially to cardiovascular defects and human ancestries influence genotype-phenotype correlation in TAAD.

Ectopia lentis in a consanguineous pakistani family and a novel locus on chromosome 8q

OBJECTIVE

To investigate the genetic basis and molecular characteristics of the isolated form of ectopia lentis.

METHODS

We ascertained a consanguineous Pakistani family with multiple individuals with ectopia lentis. All affected as well as unaffected members with isolated ectopia lentis underwent detailed ophthalmologic and medical examination. Blood samples were collected and DNA was extracted. A genome-wide scan was completed with 382 polymorphic microsatellite markers, and logarithm of odds (LOD) scores were calculated.

RESULTS

Maximum 2-point LOD scores of 5.68 and 2.88 at theta = 0 were obtained for markers D8S285 and D8S260, respectively, during the genome-wide scan. Additional microsatellite markers refined the disease locus to a 16.96-cM (14.07-Mb) interval flanked by D8S1737 proximally and D8S1117 distally.

CONCLUSIONS

We report on a new locus for nonsyndromic autosomal recessive ectopia lentis on chromosome 8q11.23-q13.2 in a consanguineous Pakistani family. Clinical Relevance Identification of genetic loci and genes involved in ectopia lentis will enhance our understanding of the disease at a molecular level, leading to better genetic counseling and family screening and possible future development of better treatment.