Re: Marfan Syndrome-what are the possible genotypes of the parents and is Marfan Syndrom dominant or recessive

Answer 1

Basically it only takes mutation in one allele to cause Marfan's. Why? Because it's autosomal dominant, specifically dominant negative. What does this mean? It means that in the heterozygous state, you are making 1/2 normal fibrillin-1, and 1/2 mutant fibrillin-1. However, normal fibrillin-1 and mutant fibrillin-1 are interacting, and the mutant is making even the normal fibrillin not functional. Dominant negatives are the result of either proteins with many subunits, or even more commonly, collagen triple helix formation (a condition called osteogenesis imperfecta). The serious problem with Marfan's is that fibrillin is not properly functioning in the aorta, and it ruptures.

Answer 2

"Marfan syndrome is an autosomal dominant disorder that has been linked to the FBN1 gene on chromosome 15. FBN1 codes for a protein called fibrillin-1, which is essential for the formation of elastic fibers found in connective tissue. Marfan syndrome is also an example of a dominant negative mutation."

This and more on Wikipedia, the free, online encyclopedia:
http://en.wikipedia.org/wiki/Marfan_Syndrome

Hope this helps!

Answer 3

Adding to the above, for a child to have Marfan's disease, one parent has to have it (the gene cannot be "silent" since it's not recessive).

At least speaking in strictly genetic terms.

However, 2-10% of cases (depending on whom you ask) of Marfan's disease are caused by random mutations sometime during embryo development. The parental genes would have had nothing to do with it, in this case -- Two parents who do not show signs of Marfan's may have a child that does. This, of course, is extremely rare.