Marfan syndrome is a systemic disorder of connective tissue with autosomal dominant inheritance and a prevalence of at least 1 in 10,000 individuals. Cardinal manifestations involve the ocular, skeletal and cardiovascular systems. While all clinical features impair quality of life, cardiovascular features are uniquely associated with early mortality due to myocardial failure or aortic rupture. Variability in the age of onset, tissue distribution, and severity of manifestations is common both in and among families. Despite major advances in the medical management of Marfan syndrome, the effectiveness of such therapies is compromised by the need for accurate and early diagnosis. It is now known the mutations in the gene on chromosome 15 encoding fibrillin (FBN1), a major glycoprotein component of the extracellular microfibril, can cause Marfan syndrome. Despite this understanding, gaps in knowledge include the molecular basis for clinical variability, the functional significance of various domains and residues of fibrillin, whether MFS truly lacks genetic heterogeneity, and the clinical spectrum that can be associated with fibrillin gene defects. The overall goal of this proposal is to gain insight into the normal and aberrant biology of the fibrillin protein (and of microfibrils) by analyzing the effects of naturally occurring mutations on clinical, cellular, and biochemical phenotypes. This will require comprehensive study of the FBN1 gene in patients with Marfan syndrome and clinically related disorders. Using refined mutation defection techniques and a novel panel of highly informative intragenic microsattelite polymorphisms for haplotype segregation analysis, it will be possible to determine whether FBN1 gene defects are associated with all cases of Marfan syndrome, to what degree allelic and/or genetic heterogeneity account for interfamilial clinical variability, and whether FBN1 gene defects underly divergent phenotypes that appear to manifest primary disruption of the elastic fiber-microfibrillar array system. By similar methods, the genes encoding other constitutive elements of extracellular microfibrils, or proteins known to associate with microfibrils, can be scrutinized as potential disease loci or as the site of sequence variants able to modify the clinical expression of mutant fibrillin alleles. Immunofluorescence and quantitative pulse-chase methods will allow determination of the cellular and protein phenotypes. In addition, much can be learned about the fundamental structural and functional properties of FBN1 domains by the study of wild-type and mutant forms using NMR spectroscopy. Finally, expression studies in cell culture and transgenic mice will allow the examination of the pathobiology of fibrillin in models that mimic the physiologic complexity of the human system. Correlation of mutant genotype to clinical, cellular, and biochemical phenotype will yield insight into the normal functions of specific fibrillin domains and residues, will enhance our understanding of pathogenesis, and should have both diagnostic and prognostic significance.
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