American Journal of Medical Genetics 47:127-135 (1993)

CONFERENCE REPORT THE SECOND INTERNATIONAL SYMPOSIUM ON THE MARFAN SYNDROME

Reed E. Pyeritz and Uta Francke

Center for Medical Genetics, Johns Hopkins University School of Medicine, Baltimore, Maryland (R.E.P.) and Departments of Genetics and Pediatrics and Howard Hughes Medical Institute, Stanford University School of Medicine, Stanford, California (U.F.)

KEY WORDS: eye, skeleton, cardiovascular system, ao r t a , ao r t i c dissection, 13- adrenergic blockade, cardiovascular surgery, f ib r i l l in , microfibrils , e las t ic f ibers , mutation, gene diagnosis, animal models

INTRODUCTION

The First International Symposium on the Marfan Syndrome, held in 1988 [Pyeritz, Am J Med Genet 32:233-238, 19891, was a largely clinical affair; only 17% of the abstracts dealt with laboratory studies, and many of those presented negative results. Similarly, of publications on Marfan syndrome listed in MEDLINE for the years 1988-1989, only 7% reported on or reviewed laboratory investigations. Nonetheless, at the First International Symposium, there was considerable optimism that the basic defect in Marfan syndrome would soon be identified. In addition, by 1988 there was preliminary but increasing evidence that the prognosis for those affected by the Marfan syndrome was improving on account of both medical and surgical therapies. Thus, it was abundantly clear at the end of the First Symposium that a follow-up meeting would be appropriate.

Received for publication March 5, 1993; revision received April 22, 1993.

Address reprint requests to R. E. Pyeritz, Department of Human Genetics, Allegheny Singer Research Institute, 320 East North Avenue, Pittsburgh, PA

0 1993 Wiley-Liss, Inc.

15212-4772

An organizing committee (Appendix) began to work in 1991 with the support of the National Marfan Foundation, and the Second International Symposium was held on 7-9 November 1992 in San Francisco, California, just before the annual meeting of the American Society of Human Genetics. This Symposium was sponsored by the National Marfan Foundation, The Johns Hopkins University School of Medicine, the Department of Genetics, Stanford University School of Medicine, and the National Institute of Arthritis, Musculoskeletal and Skin Diseases.

While the total number of citations in MEDLINE for 1991-1992 dealing with the Marfan syndrome had not changed compared to the period around the First International Symposium, the fraction of articles concerned with laboratory studies had increased considerably, to 26%. The increase was entirely due to investigations into the basic defect. This trend is magnified in the abstracts submitted to the Second International Symposium. The total number of abstracts increased nearly 50%, but the fraction devoted to laboratory studies increased from 17% to 46%.

128 Pyeritz and Francke

PHENOTYPE AND NATURAL HISTORY

Studies continue to expand the scope of pleiotropic manifestations of the Marfan syndrome. Michaels and her colleagues [this issue] emphasized the old observation that some patients have evidence of a clinical myopathy, most often evident in the face, but also in the proximal musculature. Involvement is not clinically apparent in all patients with the classic Marfan phenotype. Formal studies of prevalence, variability, and pathogenesis are clearly warranted. Savolainen and his colleagues [this issue] noted that cardiac muscle might also be affected. They documented subtle evidence of early left ventricular diastolic dys- function in children not due to valvular ab- normalities or medication.

Grahame and Pyeritz [this issue] documented the prevalence of joint hypermobility in children and adults with the Marfan syndrome and found a high prevalence of clinical complaints related to the musculoskeletal system, with most adults experiencing symptoms. Kohlmeier et al. [this issue] documented decreased bone mineral density in adult women with Marfan syndrome. This abnormality was not related to scoliosis or histo of fracture. These

suggest that patients with Marfan syndrome may be predisposed to arthropathies and orthopedic problems later in life, This notion was supported by Sponseller and his co-workers [this issue] who showed in a study of orthopedic problems in consecutive clinic patients that three times as many adults with Marfan syndrome had frequent or daily back pain compared to the general population. The frequency of symptoms was associated with scoliosis, which occurred in 60% of the study population. Another important result of their study was documentation that scoliotic curves of 40" or more did tend to progress during adulthood. Thus, patients with moderate and severe scoliosis should be followed indefinitely by monitoring degree of curvature, neurologic signs and pulmonary function.

two studies on joint 7 axity and bone density

One lesson from all of these studies was that the physician in overall charge of managing a patient with the Marfan

syndrome needs to have broad, routine concerns on both the initial and follow-up evaluations. Increasingly, neurologists and rheumatologists need to be involved with their orthopedic, cardiovascular and ophthalmological colleagues in managing the Marfan syndrome.

Severe aortic regurgitation, aortic dissection, and dissection with rupture remain the major causes of death of adolescents and adults with Marfan syndrome . T h r e e groups working independently confirmed what was long suspected that the risk of suffering a major aor t ic complication was most strongly associated with the diameter of the aortic root. While Roman and her colleagues [this issue] suggested that the rate of change of the aortic diameter was an independent and important predictor of risk, Pyeritz [this issue] and Murgatroyd e t al. [this issue] found otherwise. However, all agreed, that some patients dissect with aortic root dimensions less than 50-55 mm, and that better clinical predictors of this risk are necessary. Pyeritz found that a family history of a relative suffering dissection was the next strongest predictor of a patient's risk after the aortic root dimension. Such p a t i e n t s shou ld have prophylac t ic composite graft repair of the ascending aorta before the aortic diameter reaches 60 mm. The major limitation to surge7 at a smaller diameter remains the technique of t h e o p e r a t i o n i t se l f , a l though improvements continue to be made.

TREATMENT

The utility of chronic B-adrenergic blockade in preventing or delaying cardio- vascular complications continued to be a topic that generated much interest. The only randomized, controlled trial remained that of Pyeritz; final analysis of these data by Shores et al. [this issue] reached two conclusions. First, patients treated with pro ranolol showed a slower rate of

received no medication. Second, treated patients were less likely to die, develop aortic regurgitation or dissection, or need aortic surgery during the course of this

aortic di P atation compared to patients who

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trial compared to the control subjects. The group from Johns Hopkins, therefore, c o n t i n u e d t o r e c o m m e n d s t r o n g l y

ro hylactic use of oral f3-adrenergic Elociade. This viewpoint was supported by Alpert et al. [this issue] who showed that children in adolescence benefitted from atenolol, although their control group was not concurrent or randomized. Rosen et al. [this issue] showed in a nonrandomized, retrospective study that the rate of aortic growth was less in children with Marfan syndrome t r e a t e d with 8-adrenerg ic blockade (primarily atenolol) compared to untreated children. They did not find a similar beneficial effect in adults.

At the First International Symposium, Yin and colleagues [Circulation 79954-862, 19891 demonstrated potentially adverse effects of acute administration of a non- cardioselective f3-adrenergic blocking drug (propranolol) on aortic wall stress. On a reassuring note, Rosen and co-workers [this i s s u e ] s h o w e d t h a t c h r o n i c o r a l administration of a cardioselective B-blocker ( a t e n o l o l ) d id no t i m p a i r a r t e r i a l com liance. Phelps et al. [this issue]

adrenergic blocker in the treatment of Marfan syndrome, atenolol, needs to be a d m i n i s t e r e d a t l e a s t twice dai ly . M o r e o v e r , t h e d o s e n e e d s t o b e individualized for optimal effect.

In children with the Marfan syndrome, the most common cause of death IS severe mitral regurgitation, and this problem also is of major clinical concern in perhaps 20% of adults. Until recently, replacement of the severely regurgitant mitral valve with a prosthetic valve, followed by life-long anticoagulation, was the only option. Treatment of children with warfarin is problematic. In addition, valve replacement is often complicated by the mitral annular dilatation that usually occurs in the Marfan syndrome, which presents problems with seating the prosthesis. In the past decade, various techniques for repairing the mitral apparatus to reduce or eliminate mitral regurgitation have evolved and proven successful in managing mitral valve disease due to a number of diverse causes. The surgical group at Johns Hopkins [Gillinov et al., this issue] reported on their experience

emp K asized that the most commonly used B-

in treating the mitral valve in 33 patients over the past 8 years. EspecialIy noteworthy were the excellent results in 25 patients who underwent valve repair. Most of them underwent an annuloplasty procedure that substantially reduced the valve orifice and was stabilized by a flexible (Duran) ring. Hemodynamic i m p r o v e m e n t was d o c u m e n t e d by intraoperative transesophageal echocard- iography. Follow-up studies over an inter- mediate term suggested that mitral valve repair would be at least as successful as repairs performed for other mitral valve pathology, and eliminate the need for chronic an ticoagul a t ion. Thus, repair should be the first consideration in a Marfan pa t ien t who needs surgical management of mitral regurgitation. This approach will not be possible in some patients who have extensive annular calcification or a large number of ruptured chordae tendineae.

The life-threatening complications of severe aortic regurgitation and acute aortic dissection may occur at any age, but usually after childhood. These problems account for most of the mortality in Marfan syndrome [Murdoch JL et al., N Engl J Med 286:804-808, 19721. Application of the composite graft repair techniques first developed by Bentall [Bentall and De Bono, Thorax 23:338-339, 19681 to the Marfan syndrome has unquestionably improved the average life ex ectancy for all patients treated surgically PGott et al., Ann Thorac Surg 52:38-45, 1991; Svensson et al., Circulation 8O:I-233-242, 19891. The high-quality application and continued technical evolution of composite graft surgery were evidenced from the 6 abstracts representing experiences in the United States, Germany, and China. A long-term, multicenter follow-up study of operated patients is just being organized. As Rosen and colleagues [this issue] emphasized, not all patients who undergo technically successful operations survive 5 years, and the predictors of postoperative complications and death have not been assessed adequately. However, without much doubt, an important predictor of future morbidity and mortality is existence of aortic dissection a t the time of composite graft surgery. In this regard

130 Pyeritz and Francke

there is no consensus yet on how to manage patients after composite graft surgery. Recommendations that could be subjected to rigorous assessment in the future include: restrictions on physical activity; monitoring by echocardiography (either transthoracic or transesophageal), magnetic resonance imaging or other modalities; oral vs parenteral antibiotic

rophylaxis; and chronic administration of f; -adrenergic blockade.

COMPREHENSIVE MANAGEMENT

The Professional Advisory Board of the National Marfan Foundation has pioneered development of uniform standards for a comprehensive "Marfan Syndrome Clinic." Groups of health care professionals that wish to be recognized as a Marfan s ndrome clinic by the National Marfan Joundation must adhere to these criteria. In concise form they are: 1.

2.

3.

4.

5.

of

The clinic - should offer coordinated, mult i -discipl inary evaluat ion and management; The director should be a physician with demonstrated expertise and interest in some clinical aspect of the Marfan syndrome; All of the affiliated specialists should be willin to perform an initial eval-

ab i l i ty of t h e p a t i e n t t o pay professional fees; T h e clinic staff should b e a n educational resource for patients, health professionals, the community and the Foundation; and The clinic should have a strong com- mitment to conducting or at least facilitating scientific investigations of the Marfan syndrome and related disorders.

uation o B a patient regardless of the

Several such clinics reported on some -~ their experiences at ihe Symposium [Gasner et a]., this issue; Gilchrist et al., this issue; Niedermeyer et al., this issue]. They and Lacassie [this issue] emphasized the wide clinical spectrum of patients referred for evaluation of Marfan syndrome and the fact that most patients do not warrant that diagnosis. To assist in diagnosing and classifying patients as

having Marfan syndrome, the phenotypic criteria promulgated 5 years ago by an international committee [Beighton et al., Am J Med Genet 29581-594, 19881 should be revisited and modified on the basis of new information and experience. But there is general consensus that any "diagnostic criteria" will be arbitrary and may not apply in some individual cases because of variable expression, intralocus gene t ic he te rogenei ty and, perhaps, interlocus heterogeneity. Gasner and colleagues [this issue] presented a nascent data base designed to collect and analyze phenotypic information on unselected patients. Whether any system will fulfill the promise of improved nosology remains moo t . T h e r e a l i z a t i o n t h a t any classification scheme based solely on clinical phenotype will be inadequate, emphasized to some the need for a "laboratory diagnostic test for the Marfan syndrome."

THE MARFAN GENE: FIBRILLIN cDNA AND PROTEIN STRUCTURE

Considerable progress has been made in unraveling the underlying molecular pathology of Marfan syndrome. The two laboratories who originally reported partial cDNAs f o r t h e f ib r i l l i n gene on chromosome 15 (FBN1) [Maslen et al., Nature 352:334-337, 1991; Lee et al., Nature 352:330-334, 19911 have continued their cloning efforts. The laboratories of both L. Sakai and F. Ramirez presented nearly complete FBNl cDNA sequences that were largely in agreement. The gene structure presented by Corson et al. [this issue] includes 47 six-cysteine-containing (epidermal growth factor [EGF] precursor- like) repeats and 7 interspersed eight- cysteine (transforming growth factor-01 binding protein [TGFOlBP] like) motifs. In addition, the gene contains one internal proline-rich region, an EGF/TGFJJlBP hybrid region and unique amino and carboxyl terminal regions. The laboratory of F. Ramirez [Pereira et al., this issue] has obtained a very similar structure for FBNl and has further com ared it with the

t FBN2) on chromosome 5 of which they have cloned the 5' half. The overall

ene structure of the P ibrillin-like gene

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organization of the two FBN genes is very similar.

The currently available cDNA sequence is 9.6 kb long, close to the 10 kb transcript size estimated from Northern blot analysis. However, there is some disagreement about the translational start site since the immed- iate 5’ upstream region is extremely GC- rich and devoid of stop codons. Therefore, for the description of mutations, the codon numbering system published by Maslen et al. [1991] has continued to be used with negative numbers given to the mutations in the region 5’ to the beginning of the originally published partial sequence.

T h e laboratory of L. Sakai has continued to study the structure and f u n c t i o n of t h e f ibr i l l in molecu le [Charbonneau and Sakai, this issue]. With an antibody against a synthetic peptide of deduced amino acids from the C-terminus the investigators have been able to isolate the C-terminal peptide of fibrillin and found evidence that it is cross-linked to other specific domains of fibrillin. Since EGF-like repeats in other proteins have been shown to bind calcium, this hypothesis has also been entertained for fibrillin and direct proof of the calcium-binding was obtained by radioactive calcium ligand blotting of purified fibrillin and of proteins from human fibroblasts in culture. It seems that fibrillin binds calcium when disulfide bonds are present. Maslen et al. [this issue] have also studied the calcium-binding properties of fibrillin peptide fragments and have directly shown the presence of 13- hydroxylated asparagine residues that are postulated to be necessary for calcium- binding of EGF-like repeats. The structure of each EGF domain includes disulfide bonds between the more-or-less regularly spaced six cysteine residues; thus, missense mutations tha t remove cysteines a r e predicted to affect protein folding.

SEARCH FOR MUTATIONS IN FBNl

Since the first report by the research group at Johns Hopkins of a mutation in the fibrillin gene on chromosome 15 (FBNl), a substitution of proline for arginine at codon 239 that was present in two

unrelated patients with early onset of severe disease [Dietz e t al., Nature 352:337-339, 1991 1, additional mutations have been found in several laboratories. The R239P mutation has not been seen in any other patients. Mutations that change a cysteine residue within an EGF-like domain are the most frequent missense mutations detected in patients with Marfan syndrome. Dietz et al. [this issue] have identified 4 such mutations: C351S, C765R, C1323S, and C1409S. Tynan et al. [this issue] representing the research group of Francke at Stanford University reported a C219T substitution and Hewett e t al. [this issue] representing the laboratory of Sykes at Oxford Umversity p r e s e n t e d a C 3 2 5 T s u b s t i t u t i o n . Kainulainen et al. from Peltonen’s lab in Helsinki had previously found a C344T substitution also in an EGF-like motif [Kainulainen et al., Proc. Natl. Acad. Sci.

mutation in an 8-cysteine (TGF131BP-like) repeat was reported by Pearson et al. [this issue] in a patient with dislocated lenses, annuloaortic ectasia and aneurysm of the ascending aorta who lacked the typical Marfanoid skeletal changes but had joint contractures.

USA 8915917-5921, 19921. A C691P

Small intragenic deletions of FBNl have also been identified that ranged from a 17 bp deletion a t an intron-exon boundary [Tynan et al., this issue] and a 83 bp pair deletion creating a premature termination signal [Dietz, Pyeritz et al., this issue] to a 366 bp in-frame deletion previously reported by Kainulainen et al. [1992]. Wong et al. [this issue] from the laboratory of Godfrey identified a 123 bp in-frame deletion in the cDNA that is apparently caused by a point mutation in a donor splice site. A most unusual case of exon-skipping was reported by Dietz et al. [this issue] where a nonsense mutation, Y1215X, within an exon led to a 66 nucleotide deletion of the mRNA that constitutes part of an 8-cysteine domain. Not all nonsense mutations ead to mRNA processing defects; however, as truncated pol eptides have been observed

3’ end and leading to premature stop codon [Kainulainen et al., this issue].

repeat as a result o YF mutations located near the

132 Pyeritz and Francke

The FBNl mutations have generally been detected by systematic screening of reverse-transcribed mRNA produced by patients’ fibroblast cultures. The cDNA is then amplified in small overlapping regions and the amplification products are analyzed for nucleotide mismatches by PAGE (SSCP or heteroduplex analysis) or denaturing gradient gel electrophoresis. PCR products with apparent mismatches are sequenced e i the r direct ly o r a f t e r subcloning. Alternatively, all PCR products can be directly sequenced by automated solid-phase sequencing [Karttunen et al., this issue]. The yield of these screening procedures which have been carried out for most or all of the available cDNA sequence has been disappointingly low, with abnormalities having been found in only 10-15% of patients screened. Possible explanations include the obvious limitations of the methods used for detection. Since RT-PCR is not a quantitative procedure and also yields a product from the normal allele, absence of a product from the mutant allele could go unnoticed. For example, large genomic rearrangements such as deletions could be missed, as would mutations that cause either lack of expression of the mutant allele or significantly reduced amounts of the mutant transcript. On the other hand, Dietz et al. [this issue] found a tandem insertion of a tetranucleotide that caused reduction of the mutant transcript to only about 6% of the transcript from the wild type allele. Mutations in introns that cause abnormal splicing and degradation of unstable mRNA would also be missed. Genetic heterogeneity should further be considered as a possible cause even though most linkage studies have shown the Marfan phenotype to be linked to polymorphisms within FBNl or in the vicinity. Possible exceptions are the large French family reported by Boileau et al., [this issue] and one family studied in Helsinki, although in the former case the phenotypes are not classic Marfan syndrome, and confounding f a c t o r s ( i n t r a g e n i c r e c o m b i n a t i o n , nonpaternity, and mistakes in genotyping) have not yet been rigorously excluded in these reports.

Mutation detection methods will also turn up base changes leading to amino acid s u b s t i t u t i o n s t h a t m a y n o t b e

pathogenetically significant. Such a substitution would segreeate with the Marfan phenotype in families if the true muta t ion ( a s yet undetected) were elsewhere in the same allele. The patho- genetic significance of the N1246S [Hewitt et al., this issue], N1229Q [Kainulainen et al., this issue] or G229S [Tynan et al., this issue] mutations has been argued on the basis of the highly conserved nature of the asparagine or glycine residues in these pos i t i ons wi th in EGF- l ike repeats . Additional evidence for significance is provided by the absence of these mutations in large numbers of normal individuals. On the other hand, within Marfan syndrome families the presence of such a mutation in a mildly affected or apparently unaffected relative does not necessarily argue against its pathogenetic significance since reduced penetrance and variable expressivity are known characteristics of the Marfan gene.

ABNORMALITIES IN FIBRILLIN SYNTHESIS AND DEPOSITION

In vitro studies of the biosynthesis, secretion and deposition of fibrillin molecules in cultured dermal fibroblasts can throw further light on the effects of these putative mutations. Aoyama et al. [this issue] reported the results of studies of 50 Marfan patients usi a methodology of pulse-labelling with %S-cysteine and subsequent quantitation of labelled fibrillin protein in cell lysate, tissue culture medium and extracellular matrix deposited in the culture dish using SDS-PAGE, in an extension of methods previously reported by Milewicz et al. [J. Clin. Invest. 89:79- 86, 19921. Abnormalities were found in al- most all samples. Based on the amount of fibrillin production and deposition, patients could be subdivided into 5 distinct phenotypic groups. Fibrillin protein studies were also reported by Ragunath et al. [this issue] from the laboratory of Steinmann in Zurich. They found a truncated fibrillin, produced by the mutant FBNl gene with the 366 bp in-frame deletion [Kainulainen et al., 19921, to be present at about the same amount as the normal product. In contrast, marked reduction of fibrillin deposition in the

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extracellular matrix was seen in a patient with Marfan syndrome diagnosed at birth in whom the DNA defect is yet unknown. Cell and culture medium mixing experiments by Aoyama et al. [this issue] as well as by Ragunath et al. [this issue] showed that the presence of relatively low amounts of mutant fibrillin can significantly disturb the deposition of fibrillin into the extracellular matrix. McGookey Milewicz et al. [this issue] reported a patient with a 175 bp deletion that resulted in a premature stop codon. The mutant truncated protein was detectable in equal amounts intracellularly but its secretion from the cell was delayed.

chromosome 5 has been further confirmed [Velinov et al., this issue]. Gibson et al. [this issue] have identified a new fibrillin- like protein (FLP) in cattle with antibodies against the bovine form of FBN1. The FLP cDNA has a structure similar to that of FBNl and FBN2, from other species, and there is evidence for alternatively spliced forms of FLP. Developmental studies of the expression of FBNl, FBN2 and FLP in bovine fetal aorta and ligamentum nuchae [reported by Mecham et al., this issue] showed a pattern of e x p r e s s i o n t h a t p a r a l l e l s t h a t of tropoelastin and sug ests that fibrillins play a role in elastic fibril f ormation.

ELASTIN-ASSOCIATED MICROFIBRILS ANIMAL MODELS

Since most mutant fibrillin molecules will be incorporated into the elastin- associated microfibrils, it is essential that the aggregation of normal and abnormal fibrillin molecules and their association with o t h e r p r o t e i n s o r glycoproteins b e understood. Gibson [this issue] from the University of Adelaide, Australia, presented an overview of the microfibril-associated proteins, most of which have been isolated in his laboratory. These include GP115 115kD), AMP (32kD), MAGP (20kD), MP78 78kD), and MP25 (25 kD). With antibodies

against MAGP (microfibril-associated glycoprotein) the investigators have been able to show that this protein is present in the beads of the beaded filament structure of the microfibrils. MAGP cDNA has been isolated from bovine and human cDNA libraries, and the human gene has been mapped to lp36.1-p35 by Faraco et al. [this issue]. This gene as well as genes for other microfibril-associated glycoproteins could be candidates for mutations in Marfan families in whom linkage to FBNl has been excluded or in families with connective tissue disorders that are genetically and clinically distinct such as mitral valve prolapse syndrome or annuloaortic ectasia.

Further studies of the bovine model for Marfan syndrome were reported by Potter et al. [this issue] from Washington State University. The skeletal and ocular changes of t h e bovine Marfan-like syndrome have been reported previously [Besser et al., Am 3 Med Genet 37:159-165, 19901. Since that report, 3 cattle have died from aortic rupture, one had dissection of the aorta and pulmonary artery and one had bullous emphysema of the lung. Studies of fibrillin protein showed normal synthesis and secretion but poor incorporation into the extracellular matrix. The probe for the human polymorphic RFLP marker D15S1, which initially localized the Marfan gene by l inkage t o chromosome 15, cross- hybridized with bovine DNA and identified an RFLP that will be used for linkage studies in the cattle family [Pritchett and Potter, this issue].

Bonadio et al. [this issue], from the University of Michigan, reported progress in isolating the mouse FBNl gene. The cDNA sequenced so far shows striking homology to the human sequence and also detected a single mRNA species of 10 kb.

OTHER FIBRILLINS PHENOTYPE-GENOTYPE CORRELATIONS

Additional fibrillin-like genes and proteins may also exist. A previous report of linkage of congenital contractural arachnodactyly (CCA) to the FBN2 gene on

From the new information presented on the molecular and cellular biology of Marfan syndrome, it became abundantly

134 Pyeritz and F'rancke

clear that genotype-phenotype correlations, i.e., the relationship between specific gene mutations and the resulting phenotype at the biochemical, cellular and clinical levels, will be a formidable challenge. The relatively small number of patients (n=20) in whom a FBNl mutation that is likely to be pathogenet ical ly significant has been identified at the DNA level is in striking contrast to the very high proportion of a b n o r m a l i t i e s obse rved i n f ib r i l l i n biosynthesis, secretion or deposition. Since additional proteins contribute to the formation of microfibrils, any abnormalities in deposition could be extrinsic to the fibrillin molecule itself. Therefore, the possibility of genetic heterogeneity cannot be excluded. On the other hand, as predicted by the linkage studies of Kainulainen et al. [Am J Hum Genet 49:662- 667, 19911 that showed linkage to 15q21 markers in a number of families with quite different manifestations of the Marfan syndrome spectrum, it is likely that mutations in the fibrillin gene will be found in patients who do not meet the strict diagnostic criteria.

In order to facilitate progress in this area of research, the formation of a consortium was discussed with Lap-Chee T s u i a n d G a r r y C u t t i n g who, as representatives of the cystic fibrosis consortium, shared their experience with the attendees at the symposium. A Marfan Gene Research consortium was proposed to ensure the timely exchange of information, before publication and on a confidential basis, in order to facilitate collaborations and to prevent unnecessary duplication of effort. The plans are to collect information on patients in whom fibrillin gene mutations have been identified. Information will include the molecular defect, clinical and family history and results of biochemical and cellular studies.

IMPLICATIONS FOR DIAGNOSIS AND GENETIC COUNSELING

At the symposium, a panel consisting of clinical and molecular geneticists addressed the impact of the new molecular and cellular genetic information on the practice of diagnosis and counseling for

Marfan s drome. In families in which

polymor hic intragenic BN1 markers has clearly 1 een established, marker typing can be carried out on relatives pre- or postnatally. While there was uncertainty as to the demand for prenatal diagnosis, postnatal studies for individuals at risk are of value to distinguish those who are likely to carry the mutant gene and will r e u i r e r e g u l a r f o l l o w - u p a n d car 1 iovascular monitoring from those who are not likely to have inherited the gene. In small families in which a likely disease- causing FBNl mutation has been identified, relatives can easily be typed for the presence of this mutation and definitive counseling can be provided.

On the other hand, the panel felt strongly that in small families without a sufficient number of affected individuals to establish linkage of the disease phenotype to FBN1, and in which a FBNl gene m u t a t i o n has no t b e e n ident i f ied, diagnostic studies and counseling based on F B N l inarker typing would not be appropriate at this time because not enough information is yet available regarding genes elsewhere in the genome that could be mutated to cause a Marfan- like phenotype. For an individual with a ques t ionable d i a nosis and without

Marfan syndrome, there is not and will not soon be a DNA-based diagnostic test. Thus, the diagnostic criteria for the disorder remain based on clinical findings. If the fibrillin protein abnormalities turn out to be not only much more sensitive, as they appear to be at this time, but also specific for Marfan syndrome, which has yet to be established, it is possible that a diagnostic test could be developed along the lines of fibrillin synthesis, secretion and deposition studies. However, such a test would require skin biopsies and primary cell cultures and, thus, would be neither fast nor cheap.

FUTURE MEETINGS

$ linkage o r" the disease henotype to highly

relatives clearly a f fected with

The Third International Symposium on the Marfan syndrome is planned to be held in Berlin in September 1994. The Fourth International Symposium in 1996

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would mark the 100th anniversary of the first clinical description of the skeletal features of Marfan syndrome. It would be desirable and fitting to convene in Paris, France, where Antoine B.-J. Marfan lived and worked.

ACKNOWLEDGMENTS

This Symposium was supported by grants f rom t h e Paul and Annet ta Himmelfarb Foundation, the March of Dimes Birth Defects Foundation (4-FY92-0922), the Na t iona l Ins t i tu te of Ar thr i t i s and Musculoskeletal and Skin Diseases (R13 AR41741), and the National Marfan Foundation, for which we are extremely grateful.

APPENDIX ORGANIZING COMMITTEE

Barbara A. Bernhardt, M.S. Johns Hopkins University School of Medicine

Peter H. Byers, M.D. University of Washington School of Medicine

Anne H. Child, M.D. St. George’s Hospital Medical School

Priscilla Ciccariello National Marfan Foundation

Richard Devereux, M.D. The New York Hospital-Cornell Medical Center

Uta Francke, M.D. (Co-chair)

Maurice Godfre , Ph.D.

Stanford University School of Medicine

University o l! Nebraska School of Medicine

Vincent L. Gott, M.D. Johns Hopkins University School of Medicine

Leena Peltonen, M.D., Ph.D. National Public Health Institute of Finland

Reed E. Pyeritz, M.D., Ph.D. (Co-chair) Johns Hopkins University School of Medicine

Beat Steinmann, M.D.

Petros Tsipouras, M.D.

Children’s Hospital of Zurich

University of Connecticut School of Medicine