If you have Marfan syndrome, will they know it immediately after you are born?

Likely Not. Diagnosing marfan syndrome is based on a long list of specific criteria. Most infants will not exhibit the symptoms immediately after birth. So it is very unlikely to know immediately.
Not if mild features. Marfan syndrome persons can have mild or moderate symptoms, so they can look pretty normal as babies. The physical features of taller height, long arms, long fingers, flat feet, high-arched palate, small lower jaw, chest deformities, abnormal back curves, etc..., become more obvious later as they grow up.

Related Questions

Does being very tall mean you have Marfan syndrome?

Not Necessarily. But it is possible. A visit to the doctor with that question in mind should provide the answer. Read more...
NO,but you could. Marfan is a fairly common fenetic disorder characterized not only by tall stature but also by eye problems, cardiac problems and orthopedic problems.Usual characteristics are a long wingspan, long digits, abnormalities of breastbone and or spine, increased elastcity of skin, strech marks, small jaw, long thin face, arched palate, myopia.Abnormalities in 3 organ systems or + genetic testing needed for dx. Read more...

How dangerous is Marfan syndrome?

Marfan syndrome. affects the body's connective tissue and can cause problems in the eyes, joints, and heart. Marfan syndrome has no cure, but doctors can provide symptomatic management. Read more...