Clinical and linkage study of a large family with simple ectopia lentis linked to FBN1

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

BACKGROUND

Previous studies demonstrated that patients with different FBN1 mutations often present more considerable phenotypic variation compared to different members of the related family carrying a same mutation. The purpose of our study was to identify pathogenic mutation and provide more information about genotype-phenotypic correlations in a large Chinese family with Marfan syndrome.

METHODS

15 related family members from a Chinese 4-generation pedigree with Marfan syndrome underwent physical, ophthalmologic, radiological and cardiovascular examinations. The propositus has De Bakey III aortic dissection and didn't fulfill the revised Ghent criteria for Marfan syndrome. Nine family members have ectopia lentis and their echocardiogram was normal. Five other family members have no evidence of Marfan syndrome. Genomic DNA was isolated from blood leukocytes. The exome sequencing was employed on the propositus, then the Sanger sequencing was conducted for mutation verification in other 14 participants of this family.

RESULTS

The causative mutation in FBN1 discovered in the propositus was a known heterozygous missense mutation, c.1633T>G (p.R545C), in exon 14 (NM 000138). This same mutation was also identified in all 9 ectopia lentis patients and one unaffected 8-year-old girl. However, the same mutation was not discovered in other 4 unaffected family members.

CONCLUSIONS

Our data enhance the information of genotype-phenotype correlation owing to FBN1 mutations. To our current knowledge, we firstly reported that the same FBN1 mutation, c. 1633C>T (Arg545Cys), was detected simultaneously in three different cardinal phenotypes (ectopia lentis, aortic dissection and unaffected) within one family. The unaffected girl with FBN1 mutation may presumably represent a rare case of nonpenetrance.

Molecular pathogenesis and management strategies of ectopia lentis

Ectopia lentis (EL) is a condition that can either herald underlying systemic conditions, or be isolated. The recent expansion in the genetics of these conditions has furthered the understanding of the underlying molecular aetiology. It is becoming apparent that novel genes, and in particular the ADAMTS (a disintegrin and metalloproteinase with thrombospondin motifs) family, are important in ocular development. The common link in these genes seems to be EL. The clinical management of EL is challenging. In particular, the options for addressing surgically induced aphakia in the context of an ectopic capsule are varied. Little evidence exists to direct management of these issues. This review summarises the molecular pathogenesis of EL and conditions associated with it, using the genetic aetiology as a framework. Furthermore, it summarises some of the issues involved in its clinical management.

Improving clinical recognition of Marfan syndrome

BACKGROUND

Marfan syndrome is a potentially fatal disorder with cardiovascular, skeletal, and other manifestations that may also be seen in individuals without Marfan syndrome, making diagnosis difficult. Our goals were (1) to examine the ways in which patients have been recognized as having Marfan syndrome, (2) to examine the prevalence of current diagnostic findings, and (3) to determine which physically evident features are most sensitive and specific for referral to confirm a diagnosis of Marfan syndrome.

METHODS

Between 2005 and 2007, we prospectively studied 183 consecutive patients with identified Marfan syndrome (Marfan group) and 1257 orthopaedic patients and family members (non-Marfan group). For the Marfan group, we recorded age at the time of recognition and the methods by which the syndrome was recognized; we used Ghent criteria to identify physically and radiographically evident features. For the non-Marfan group, we examined for Ghent criteria that could be noted on the basis of a routine history, physical examination, or radiographs. We used means, odds ratios, and frequencies to analyze the diagnostic use of each finding (alpha = 0.05).

RESULTS

According to the Ghent criteria, 27% of patients in the Marfan group (mean age at the time of diagnosis, 7.3 years) had major skeletal involvement whereas 19% had zero or one skeletal feature. The most common physical features were craniofacial characteristics, high-arched palate, positive thumb and wrist signs, and scoliosis. In the non-Marfan group, 83% had one skeletal feature, 13% had two skeletal features, and 4% had three skeletal features or more. The physical features with the highest diagnostic yield were craniofacial characteristics, thumb and wrist signs, pectus excavatum, and severe hindfoot valgus.

CONCLUSIONS

Musculoskeletal clinicians should be aware of the diagnostic features of Marfan syndrome. Patients with three to four physically evident features, or two highly specific features (e.g., thumb and wrist signs, craniofacial features, dural ectasia, or protrusio), should be carefully reexamined and possibly referred for an echocardiogram or a genetics consultation.

LEVEL OF EVIDENCE

Diagnostic Level II. See Instructions to Authors for a complete description of levels of evidence.

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.

Unique phenotype in a Chinese family pedigree: ectopia lentis with varicose great saphenous vein

OBJECTIVE

To report a Chinese family affected with both ectopia lentis and varicose great saphenous vein.

DESIGN

Observational pedigree report.

PARTICIPANTS

The family with a total of 53 members in five generations. In the kindred there were 16 affected adults (including 6 deceased), of which 7 were male and 9 were female.

MAIN OUTCOME MEASURES

Patients in this family showed an autosomal dominant trait of ectopia lentis and varicose great saphenous vein, occurring in four successive generations. The onset ages for lens dislocation were between 38 and 52 years. No cardiovascular abnormality was observed. Four patients underwent intracapsular lens extraction surgery.

CONCLUSIONS

The phenotype of this family showed similarities with Marfan-related disorders. This is a unique phenotype of ectopia lentis with varicose great saphenous vein.

The roles of two novel FBN1 gene mutations in the genotype-phenotype correlations of Marfan syndrome and ectopia lentis patients with marfanoid habitus

Mutations in the fibrillin-1 (FBN1) gene have been identified in patients with Marfan syndrome (MFS) and Marfan-like connective tissue disorders. In this study, two Chinese families were recruited. The patients in family 1 were well characterized with MFS, while those in family 2 displayed Marfan-like disorders such as ectopia lentis (EL) and marfanoid habitus, but did not develop cardiovascular diseases. We aimed to analyze the pathogenic mutations and their relationships with phenotypes in these two Chinese families. All participants underwent complete physical, ophthalmic, and cardiovascular examinations. The 65 exons and flanking intronic sequences of FBN1 were amplified by polymerase chain reaction, and screened for mutations by denaturing high-performance liquid chromatography and sequencing. One hundred and fifteen unrelated controls were analyzed using the same methods to confirm the mutations. In family 1, we identified the mutation p.C499S in the calcium-binding epidermal growth factor (cbEGF)-like domain 3 of FBN1. In family 2, the mutation p.C908Y was identified in an interdomain region of the hybrid motif 2 linked to the cbEGF-like domain 10. It can be concluded that FBN1 mutations involving cysteine substitutions are usually associated with MFS and EL with some MFS features. Moreover, pathology seemed more serious when the mutations disrupted the three disulfide bridges in the cbEGF-like domains, which was more likely to cause typical MFS than if the mutations occurred in the hybrid motifs. Our data preliminarily establish a genotype-phenotype correlation in the diagnostic process of MFS and predominant EL with Marfan-like features.

Ectopia lentis phenotypes and the FBN1 gene

Mutations of the fibrillin-1 (FBN1) gene on chromosome 15 have been described in patients with classical Marfan syndrome (MFS), neonatal MFS, the "MASS" phenotype, autosomal dominant ascending aortic aneurysms, autosomal dominant ectopia lentis (EL), Marfanoid skeletal features [Milewicz et al., 1995: J Clin Invest 95:2373-2378], familial arachnodactyly, Shprintzen-Goldberg syndrome [Hayward et al., 1994: Mol Cell Probes 8:325-327; Furthmayr and Francke, 1997: Semin Thorac Cardiovasc Surg 9:191-205], and severe progressive kyphoscoliosis [Adès et al., 2002: Am J Med Genet 109:261-270]. We report the use of denaturing high performance liquid chromatography (DHPLC) to facilitate the characterization of a previously elusive FBN1 mutation in the large autosomal dominant EL kindred described by Edwards et al. [1994: Am J Med Genet 53:65-71]. This isolated EL kindred remains the largest for which detailed clinical data is available. Nine years on, we present an update of the clinical status of the family. We report a recurrent FBN1 mutation, R240C, in the kindred. This mutation has been reported three times before, once in a family with classic MFS [Loeys et al., 2001: Arch Intern Med 161:2447-2454], once in one member of a multi-generation EL kindred, [Körkkö et al., 2002: J Med Genet 39:34-41], and once in an adult from a familial EL kindred who had EL, and involvement of the integument, without cardiovascular involvement [Comeglio et al., 2002: Br J Ophthalmol 86:1359-1362]. This is the second report of the R240C mutation in association with isolated EL, and supports the existing evidence that the R240C mutation can result in two quite distinct, yet related, phenotypes. It also raises the possibility that R240C may prove to be a relative mutational "hot-spot" for isolated EL. We review the current literature regarding EL (isolated and other) and FBN1 mutations.

The Marfan syndrome

The Marfan syndrome (MFS), initially described just over 100 years ago, was among the first conditions classified as a heritable disorder of connective tissue. MFS lies at one end of a phenotypic continuum, with people in the general population who have one or another of the features of MFS at the other end, and those with a variety of other conditions in between. Diagnosis of MFS and these other conditions remains based on clinical features. Mutations in FBN1, the gene that encodes fibrillin-1, are responsible for MFS and (in a few patients) other disorders in the continuum. In addition to skeletal, ocular, and cardiovascular features, patients with MFS have involvement of the skin, integument, lungs, and muscle tissue. Over the past 30 years, evolution of aggressive medical and surgical management of the cardiovascular problems, especially mitral valve prolapse, aortic dilatation, and aortic dissection, has resulted in considerable improvement in life expectancy.

The molecular genetics of Marfan syndrome and related microfibrillopathies

Mutations in the gene for fibrillin-1 (FBN1) have been shown to cause Marfan syndrome, an autosomal dominant disorder of connective tissue characterised by pleiotropic manifestations involving primarily the ocular, skeletal, and cardiovascular systems. Fibrillin-1 is a major component of the 10-12 nm microfibrils, which are thought to play a role in tropoelastin deposition and elastic fibre formation in addition to possessing an anchoring function in some tissues. Fibrillin-1 mutations have also been found in patients who do not fulfil clinical criteria for the diagnosis of Marfan syndrome, but have related disorders of connective tissue, such as isolated ectopia lentis, familial aortic aneurysm, and Marfan-like skeletal abnormalities, so that Marfan syndrome may be regarded as one of a range of type 1 fibrillinopathies. There appear to be no particular hot spots since mutations are found throughout the entire fibrillin-1 gene. However, a clustering of mutations associated with the most severe form of Marfan syndrome, neonatal Marfan syndrome, has been noted in a region encompassing exons 24 to 32. The gene for fibrillin-2 (FBN2) is highly homologous to FBN1, and mutations in FBN2 have been shown to cause a phenotypically related disorder termed congenital contractural arachnodactyly. Since mutations in the fibrillin genes are likely to affect the global function of the microfibrils, the term microfibrillopathy may be the most appropriate to designate the spectrum of disease associated with dysfunction of these molecules. The understanding of the global and the molecular functions of the fibrillin containing microfibrils is still incomplete and, correspondingly, no comprehensive theory of the pathogenesis of Marfan syndrome has emerged to date. Many, but not all, fibrillin-1 gene mutations are expected to exert a dominant negative effect, whereby mutant fibrillin monomers impair the global function of the microfibrils. In this paper we review the molecular physiology and pathophysiology of Marfan syndrome and related microfibrillopathies.

The genetic basis of aortic disease. Marfan syndrome and beyond

The Marfan syndrome and related disorders are systemic disorders of connective tissue. Proximal aorta is usually dilated. The molecular basis of Marfan syndrome has been elucidated, thus allowing prenatal diagnosis. Life expectancy has markedly improved due to the widespread use of beta-adrenergic receptor inhibitors and improved surgical management of the aortic disease.

Summary of ocular genetic disorders and inherited systemic conditions with eye findings

Of the close to 10,000 known inherited disorders that affect humankind, a disproportionately high number affect the eye. The total number of genes responsible for the normal structure, function, and differentiation of the eye is unknown, but the list of these genes is rapidly and constantly growing. The objective of this paper is to provide a current list of mapped and/or cloned human eye genes that are responsible for inherited diseases of the eye. The ophthalmologist should be aware of recent advances in molecular technology which have resulted in significant progress towards the identification of these genes. The implications of this new knowledge will be discussed herein.