European Journal of Human Genetics (2002) 10, 673 – 681 ª 2002 Nature Publishing Group All rights reserved 1018 – 4813/02 $25.00 www.nature.com/ejhg REVIEW Marfan syndrome in the third Millennium Gwenae¨lle Collod-Be´roud1 and Catherine Boileau*,1,2 1INSERM U383, Universite´ Paris V, Hoˆpital Necker-Enfants Malades, 149-161 rue de se`vres, 75743 Paris Cedex 15, France; 2Laboratoire de Biochimie, d’Hormonologie et de Ge´ne´tique Mole´culaire, Hoˆpital Ambroise Pare´ AP-HP, 9 av Charles de Gaulle, 92104 Boulogne Cedex, France The Marfan syndrome (MFS) is a prominent member of heritable disorders of connective tissue with manifestations involving primarily the skeletal, ocular and cardiovascular systems but also and less systematically investigated the lung, skin and integument, and dura. Over the last two decades, a considerable amount of clinical, molecular and protein data had accumulated. In combination with the study of natural and transgenic animal models, this new information provides greater insight into the pathogenic mechanisms underlying not only the pleiotropic manifestations of MFS but also the important degree of clinical variability (age of onset and severity) observed between patients. The following aspects will be described in this review: the structure and function of fibrillin-1; the fibrillin proteins; mutations in the FBN1 gene and pathogenic mechanisms; animal models. Finally, the currently available laboratory diagnostic tests and their limits will be discussed. European Journal of Human Genetics (2002) 10, 673 – 681. doi:10.1038/sj.ejhg.5200876 Keywords: Marfan syndrome; MFS; FBN1; fibrillin-1; review; structure Introduction guish classic Marfan syndrome from many related A hundred years have now elapsed since Dr Antonin disorders. These criteria constitute what is currently referred Marfan1 reported on the case of Gabrielle P thus describing to as the ‘Berlin nosology’.2 Patients are diagnosed based on some of the skeletal features that today define the involvement of the skeletal system and two other systems syndrome that carries his name. Since then, substantial with at least one major manifestation (ectopia lentis, aortic progress has been made with respect to the description of dilation/dissection, or dural ectasia). Patients with an the pleiotropic manifestations of this disease, the under- affected first degree relative are required to have involve- standing of underlying pathophysiological mechanisms ment of at least two other systems with one major and the availability of prevention and treatment of major manifestation preferred but not required. complications. This nosology has been found wanting in many indivi- dual cases, and revised criteria were subsequently Nosology: What is Marfan syndrome today? proposed that constitute the ‘Ghent nosology’.3 This new Marfan syndrome (MFS, OMIM 154700) is an autosomal formulation requires involvement of three systems with dominant connective tissue disorder that has an estimated two major diagnostic manifestations. It provides for major incidence of 1/5000 with probably over 25% of sporadic skeletal manifestations and considers affected first-degree cases. The syndrome involves many systems (skeletal, relatives or molecular data as major diagnostic criteria. ocular, cardiovascular, pulmonary, skin and integument, Finally, development of preventive measures and surgery and dura) but its more prominent manifestations are skele- for aortic aneurysms and dissection have lead to treatment tal, ocular and cardiovascular. In 1986, an international of life-threatening cardiovascular complications associated group of experts agreed upon diagnostic criteria to distin- with the Marfan syndrome and have considerably altered life expectancy for patients. Interestingly, the review of *Correspondence: C Boileau; INSERM U383, CHU Necker-Enfants the medical problems of surviving patients has revealed Malades, Clinique Maurice LAMY, 149-161, rue de se`vres, 75743 Paris possible unidentified pleiotropic manifestations of the Cedex 15, France. Tel: 33 14449 4485; Fax: 33 14783 3206; E-mail: [email protected] Marfan syndrome or manifestations that could be related Received 30 January 2002; revised 16 July 2002; accepted 18 July 2002 to aging of this population. These medical problems Marfan syndrome in the third Millennium GCollod-Be´roud and C Boileau 674 include the onset of arthritis at an early age, varicose veins, mRNA that encodes a 2871 amino acid protein.10,11,13,14 ruptured or herniated discs, and prolapse of the uterus or Three additional alternatively-spliced exons, likely untrans- bladder in women. These medical problems now need to lated, were found upstream of exon 1.15 Conservation of be properly investigated and monitored. nucleotide sequences within this region between human, The continued efforts to redefine diagnostic criteria mouse and porcine suggests that this region of the gene emphasize persistent shortcomings. The phenotype of the may harbour important regulatory elements. This region Marfan syndrome remains incompletely defined. Most is GC-rich, contains a CpG island, and lacks conventional manifestations are age-dependent and are difficult to quan- TATA or CCAAT boxes. tify. The Ghent nosology has been field-tested in The The deduced primary structure reveals a highly repetitive National Institutes of Health.4 Their study shows that protein that contains essentially three repeated modules 19% of patients diagnosed under the Berlin criteria failed (Figure 1): to meet the Ghent standard. Molecular data are important to better characterise this subset and to study its natural . The first repeated module is the EGF-like module that is history. homologous to one found in the Epidermal Growth Fac- tor. These modules contain six cysteine residues that form The Marfan syndrome and FBN1 three intra-domain disulfide bonds. There are 47 of these Scientists, as early as 1931, suggested that the basic defect throughout the fibrillin-1 protein. Among these, 43 con- in Marfan syndrome lay in a defect in the mesoderm.5 In tain a conserved consensus sequence for calcium binding 1955, Victor McKusick considered the syndrome as a promi- and are called cb EGF-like modules. In these domains, the nent member of the new nosologic group he named ‘the residues putatively involved in calcium binding are num- heritable disorders of connective tissue’.6 The Marfan bered sequentially in Figure 2 as in Dietz and Pyeritz.16 syndrome was long considered to be due to a defect either They include the aspartic acid at position 2, glutamic acid in one of the collagens or elastin since abnormalities in at position 5, asparagine at position 10 and tyrosine or their fibres were reported in affected subjects. However, phenylalanine at position 15. protein and gene studies conclusively demonstrated that . The second repeated module, found seven times inter- neither was involved. In 1986, Sakai and co-workers identi- spaced with cb EGF-like in the protein, is called TGF fied a new extracellular matrix protein that they named b1-binding protein-like module (TGF b1-BP-like mod- ‘fibrillin’7 (OMIM 134797). This protein is the major ule) since it is homologous to modules found in the component of microfibrils, structures found in the extracel- Transforming Growth Factor-b1 binding protein. This do- lular matrix either as isolated aggregates or closely main appears to be limited to proteins that localise to associated with elastin fibres. Ultrastructurally, microfibrils matrix fibrils (fibrillins and latent transforming growth display a typical ‘beads-on-a-string’ appearance consisting factor b-binding proteins (LTBPs)). These modules contain of a long series of globules connected by multiple filaments. eight cysteine residues. The fourth TGF-b1-BP-like module In 1990, Hollister et al., using a monoclonal antibody contains the RGD sequence which can interact with cell against fibrillin, reported abnormalities of the microfibrillar receptors.17 No specific function has yet been ascribed system in the Marfan syndrome.8 The following year, the to these modules. However, some evidence suggests that gene encoding fibrillin-1 (FBN1) was cloned and the first these domains mediate specific protein – protein interac- mutations in the gene were identified in Marfan syndrome tions.18 patients.9–11 Interestingly, the year before the FBN1 gene . Finally, the protein contains a third module consisting of was cloned, Kainulainen et al.,12 demonstrated through approximately 65 amino acids, and found twice in the linkage analysis that the gene involved in classic complete protein. These are called ‘hybrid modules’ since they forms of the Marfan syndrome was located on human chro- combine features of the EGF-like and the TGF-b1-BP-like mosome 15 precisely where the FBN1 gene was later modules. This module is also found in LTBPs, which have located. Therefore the identification of the gene defect in a single hybrid domain. Marfan syndrome is a rare example in which both posi- tional and functional cloning strategies converged rapidly Finally the protein contains three unique regions: a proline- to identify a disease gene. rich region that may act as a ‘hinge-like’ region13 and the amino and carboxy terminal domains. The N- and C-term- The FBN1 gene and other members of the fibrillin inal domains of the fibrillins display two prominent family features: the presence of an even number of cysteine resi- The gene encoding type 1 fibrillin (FBN1) lies on the long dues, four in the N-terminal and two in the C-terminal arm of chromosome 15 at 15q15 – q21.1. This very large and the presence of the basic consensus sequence for gene (first estimated at 110 kb, now at over 230 kb (Human processing by furin-types enzymes BXBB (B=basic amino Genome Sequencing Project NT 034890 sequence)) is acid residue, K or R) in each domain. The 4-cysteine highly fragmented into 65 exons, transcribed in a 10 kb domain in the N-terminus of fibrillins is homologous to European Journal of Human Genetics Marfan syndrome in the third Millennium G Collod-Be´roud and C Boileau 675 Figure 1 Schematic representation of the deduced primary structure of fibrillin-1.