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Mass Phenotype
MASS stands for: mitral valve prolapse, aortic root diameter at upper limits of normal for body size, stretch marks of the skin, and Skeletal features. It is caused by a mutation in the gene called fibrillin-1 that tells the body how to make an important protein found in connective tissue. Someone with MASS phenotype has a 50 percent chance of passing the gene along to each child. MASS Phenotype affects different people in different ways. People with features of MASS Phenotype should see a doctor who knows about connective tissue disorders for an accurate diagnosis; often this will be a medical geneticist. It is very important that people with MASS Phenotype get an early and correct diagnosis so they can get the right treatment.

Mitral valve prolapse may be present in MASS phenotype. This is when the flaps of one of the heart’s valves (the mitral valve, which regulates blood flow on the left side of the heart) are “floppy” and don’t close tightly. Aortic root diameter may be at the upper limits of normal for body size, but unlike Marfan syndrome there is not progression to aneurysm or predisposition to dissection. Skin may show stretch marks unrelated to weight gain or loss (striae). Skeletal features, including curvature of the spine (scoliosis), chest wall deformities, and joint hypermobility, may be present. People with MASS Phenotype have myopia, also known as nearsightedness.

Similarities and differences between Mass phenotype and Marfan syndrome
MASS Phenotype is a connective tissue disorder that is similar to Marfan syndrome.

MASS syndrome and Marfan syndrome are overlapping connective tissue disorders. Both can be caused by mutations in the gene encoding a protein called fibrillin. These conditions share many of the same signs and symptoms including long limbs and fingers, chest wall abnormalities (indented chest bone or protruding chest bone), flat feet, scoliosis, mitral valve prolapse, loose or hypextensible joints, highly arched roof of the mouth, and mild dilatation of the aortic root.

Individuals with Marfan syndrome have progressive aortic enlargement or lens dislocation. Unlike Marfan syndrome, skin involvement in MASS syndrome is typically limited to stretch marks (striae distensae). Also, the skeletal symptoms of MASS syndrome are generally mild.