Syndromes Marfan

EGF-like domains were identified in extracellular proteins such as fibrillin-1. EGF-modules contain about 40-45 amino acids including six cysteine residues which normally build S-S disulfide bond bridges. Mutations in the fibrillin-1 gene cause Marfan syndrome and related disorders. 

MARFAN SYNDROME IS DUE TO MUTATIONS IN THE GENE FOR FIBRILLIN, A PROTEIN PRESENT IN MICROFIBRILS... 

Figure 48-2. Probable sequence of events in the causation of the major signs exhibited by patients with Marfan syndrome (MIM 154700).

Fibrihin is located in microfibrils. Mutations in the gene for fibrihin cause Marfan syndrome. 

Scriver CR et al (editors) The Metabolic and Molecular Bases of Inherited Disease, 8th ed. McGraw-Hill, 2001 (This comprehensive four-volume text contains chapters on disorders of collagen biosynthesis and structure, Marfan syndrome, the mucopolysaccharidoses, achondroplasia, Alport syndrome, and craniosynostosis syndromes.)... 

Blindness (several forms) Deafness (several forms) Marfan syndrome Achondroplasia Neurofibromatosis Myotonic dystrophy Tuberous sclerosis All others... 

The name of a physician or researcher, often the first person to describe the disorder (for example, Marfan syndrome, which was named after Dr. Antoine Bemard-Jean Marfan)... 

D. Will not develop Marfan syndrome but will be a carrier of the disease allele... 

Molecular analysis of the fibrillin gene in these family members identified the mutation associated with Marfan syndrome as a single base substitution at the 3 end of exon 2. The result of this substitution was a deletion of the entire exon 2 firom the mRNA, and consequently 41 amino acids from the fibrillin protein. The mutation was most likely a... 

Answer A. Comparison of the RFLP patterns of 11-3 and III-2 indicates that the upper (laiger) fragment is associated vrith the disease-producing allele. This can be confirmed by looking at other affected family members. Because the fetus, IV-1, has inherited this fragment from the mother and the disease is dominant, the fetus will develop Marfan syndrome. 

A 10-year-old girl is diagnosed with Marfan syndrome, an autosomal dominant condition. An extensive review of her pedigree indicates no previous family history of this disorder. The most likely explanation for this pattern is... 

Mitochondrial genes are not known to affect the expression of Marfan syndrome (choice C). 

Marfan syndrome is an excelient example of pleiotropy (choice E), but this principle refers to the fact that a single mutation can affect multiple aspects of the phenotype, so it would not explain the pattern observed in this pedigree. 

Figure 11-6-1. A Three-Generation Family in Which Marfan Syndrome Is Being nransmitted...

While certain behavioral and nonbehavioral diseases are believed to be monogenic, diseases such as Huntington s, cystic fibrosis, Marfan, and Hirschsprung result in the specified disease, and the outward appearance or result (phenotype) of the disease varies between individuals. For instance, for Marfan syndrome, there is a level below which the mutant protein does not exhibit itself in an outward manner. Most of these diseases have modifier genes that cause modifications in the outward demonstration of the disease and play a key role in the clinical symptoms. Further, the particular metabolic pathways are often varied, with several of the steps being important and the importance of each mechanistic pathway may differ with every individual. 

The answer is D. The most likely diagnosis in this case is CPT-II deficiency, although this is apparently a fairly mild case. The patient s muscle weakness and brown urine (myoglobinuria) are characteristic of this disorder. CPT-I deficiency would most likely manifest as liver dysfunction. A secondary form of carnitine deficiency due to exogenous factors such as malnutrition, infection, or dialysis, is unlikely. MCAD ordinarily manifests within the first 3-5 years of life. The patient s normal stature is inconsistent with Marfan syndrome, which is characterized by tall stature and very long bones in the extremities. 

Dominant negative effect, when the mutant protein interferes with function of the normal protein Osteogenesis imperfecta and the collagen 1A gene (COLIAI) Marfan syndrome and the fibrillin-1 gene (FBNI)... 

Marfan syndrome is a connective tissue disorder with manifestations in many organs, but especially the skeleton, blood vessels, eyes, and lungs. 

Marfan syndrome arises from a mutation in the gene encoding fibrillin- 7IFBN... 

The pattern of inheritance of Marfan syndrome is autosomal dominant due to the failure of elastic fibers to assemble properly upon interaction of mutant fibrillin with normal elastin. 

The upper segment is the distance from the top of the head to the top of the pubic symphysis the iower segmen t is the distance from the top of the pubic symphysis to the fioor. The upper segment to lower segment ratio in persons with Marfan syndrome is iow (< 0.9) because the arms and iegs are iong reiative to the torso. 

Characteristic ocuiar features of Marfan syndrome, such as ectopia lentis (upward iens disiocation instead of downward disiocation as in homocystinuria) and myopia, arise from the effects of defective fibriiiin in the eiastic fibers of the iens. 

L3. Liu, W. O., Oefner, P. J., et al. Denaturing HPLC-identified novel FBNl mutations, polymorphisms, and sequence variants in Marfan syndrome and related connective tissue disorders. Genet. Test. 1(4), I il-lAl (1997). 

Function and location of elastin Cause of Marfan syn drome Elastin is a connective tissue protein with rubber-like properties. Elastic fibers composed of elastin and glycoprotein microfibrils, such as fibrillin, are found in the lungs, the walls of large arteries, and elastic ligaments. [Note Mutations in the fibrillin gene are responsible for Marfan syndrome]... 

Fibrillin microfibrils are widely distributed extracellular matrix assemblies that endow elastic and non elastic connective tissues with long-range elasticity. They direct tropoelastin deposition during elastic fibrillogenesis and form an outer mantle for mature elastic fibers. Microfibril arrays are also abundant in dynamic tissues that do not express elastin, such as the ciliary zonules of the eye. Mutations in fibrillin-1—the principal structural component of microfibrils—cause Marfan syndrome, a heritable disease with severe aortic, ocular, and skeletal defects. Isolated fibrillin-rich microfibrils have a complex 56 nm beads-on-a-string appearance the molecular basis of their assembly and... 

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