Hypermobility Types of HMS Marfan Syndrome Marfan syndrome: Gene and Inheritance Marfan syndrome is relatively rare, affecting about 1 in every 4000-5000 people. There is usually a family history of the condition affecting at least one parent. However about 1 in 4 cases may be the first in the family. This is because a new (‘spontaneous’) gene defect has occurred during the earliest stages of that persons’ embryonic development. The condition has an ‘autosomal dominant’ pattern of inheritance, which means that a parent with MFS has a 50:50 chance of passing on the faulty gene to each of their children. Although there is a gene test that can help support the diagnosis there are two very important things to be aware of: The finding of a defective gene does not give any indication as to how serious the condition might be. This is because ‘expression’ of the gene varies between individuals, even in the same family. Offspring may only have very mild problems and symptoms, even if a parent has a lot of problems. A negative test does not completely rule out concern. This is because there are so many gene defects that the relevant one may be so rare or brand new that it cannot be found using the tests undertaken. In most cases a diagnosis of MFS will be based on a detailed physical examination and assessment of the medical and family history. (Review date August 2019) If you would like the clinical references for the information used in this article, please contact us via the Information Standards Enquiry from.