Could the doctor have detected marfan's syndrome via the echocardiogram?

Sometimes yes: A cardiologist can suspect Marfan syndrome if a person has heart structural abnormalities sometimes seen in Marfan syndrome, combined with other bodily features suggesting Marfan syndrome, and/or combined with a family history of relatives having Marfan syndrome signs and symptoms.

Not specifically: Though certain cardiac abnormalities such as aortic root disease and mitral valve prolapse occur in patients with marfan's syndrome, the abnormalities are not completely diagnostic if found on echocardiogram. Marfan's diagnosis starts with characteristic body features.