Among weaknesses of the connective tissue, Marfan's Syndrome (MfS) occupies a particular position. It is a congenital disorder which goes through a chronic progression with advancing age. It is not curable and affects several organ systems simultaneously, the most prominent being the muscular-skeletal system, the eyes and the cardio-vascular system.

As far as the muscular-skeletal system is concerned, the most marked symptoms are tall and slim stature with extremely flexible joints (dolichostenomelia), very little muscular mass, deformities of the thorax including "keeled or chicken breast" (pectus carinatum) or "hollowed or funnel breast" (pectus excavatum), and deformities of the spine (scoliosis).

In the eyes, the lenses are often shifted upwards (lens subluxation) and are tremulous, an effect described as "iridodonesis".
Charateristic disorders of the cardio-vascular system are extreme flexibility of the heart valves (e.g. prolapse of the mitral valve) right through to insufficiency (incomplete closure of heart valves), vascular dilatation (aneurysm or ectasia)and winding course of blood vessels (elongation, loops). It is particularly the vascular dilatations which bear the danger of an unexpected life-threatening occurence (dissection or rupture).

A number of other organ systems are also effected by Marfan's Syndrome. Thus patients, because of weak connective tissue in the nasal-pharyngeal space may suffer from sleep apnoea, even during childhood, and this can have wide repercussions on their everyday lives (e.g. common complaint of extensive tiredness during the day).