Glesby and Pyeritz (1989) pointed out that more than half of a large number of patients evaluated in the medical genetics clinic at Johns Hopkins for a possible heritable disorder of connective tissue could not be precisely classified. ... Glesby and Pyeritz (1989) pointed out that more than half of a large number of patients evaluated in the medical genetics clinic at Johns Hopkins for a possible heritable disorder of connective tissue could not be precisely classified. As a group, these patients showed many manifestations of the Marfan syndrome (154700), including long limbs, deformity of the thoracic cage, striae atrophicae, mitral valve prolapse, and mild dilatation of the aortic root. Clinical clustering did not emerge when patients were stratified by mitral valve prolapse or aortic dilatation. The clinical phenotype of patients with mitral valve prolapse constituted a continuum, from Marfan syndrome at one extreme to isolated mitral valve prolapse due to myxomatous change of the valve leaflets (see 157700). In the absence of biochemical or DNA markers, the diagnosis of the Marfan syndrome was impossible when a patient had mitral valve prolapse and mild aortic root dilatation but no ectopia lentis or family history of definite Marfan syndrome. Glesby and Pyeritz (1989) suggested that until subclassification based on genetic and biochemical indicators is possible, these patients should be considered as having an overlap heritable connective disorder. They further suggested the acronym 'MASS phenotype' to designate the involvement of the mitral valve, aorta, skeleton, and skin.