[Marfan syndrome].

Marfan's syndrome is a monogenetic disease with an autosomal dominant transmission generally accompanied by type I fibrillin abnormality. This widely-distributed molecule participates in the structure of connective tissues so that any aberration may result in disease of many systems: skeletal morphology, dislocation of the lens, neurological or cutaneous signs and dilatation of the aorta predisposing to dissection, mitral valve prolapse being a common association. The diagnosis, clinical because of the size of the culprit gene and the multiplicity of the possible mutations, is sometimes difficult, and diagnostic criteria have been proposed. It is important to make the diagnosis because treatment is based on the restriction of violent exercise, betablocker therapy and regular echocardiographic monitoring of the ascending aorta, the region at highest risk of dilatation and dissection. A family enquiry is essential to make the diagnosis before the onset of complications in pauci-symptomatic patients (great intra-familial variability). Pregnancy poses special problems in these patients.