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Congenital contractural arachnodactyly represents a broad spectrum of characteristics. The features are quite variable, both within and between families. The classic form is characterized by a Marfan-like appearance (tall and slender with arm span exceeding height), arachnodactyly (long slender fingers and toes), 'crumpled' ears, contractures of major joints from birth (particularly knees, elbows, fingers, toes, and hips), bowed long bones, muscular hypoplasia (underdeveloped muscles), kyphosis/scoliosis, aortic root dilation, and various craniofacial abnormalities (such as micrognathia, high arched palate, scaphocephaly (premature fusion of the sagittal suture of the skull leading to a long, narrow head), brachycephaly (premature fusion of the coronal suture, leading to a short skull), and frontal bossing).
At the most severe end of the spectrum is a rare type with very few reported cases. In addition to the typical skeletal findings (arachnodactyly, joint contractures, scoliosis) and abnormally shaped ears, infants with the severe/lethal form have multiple cardiovascular and gastrointestinal abnormalities.
Congenital contractural arachnodactyly is caused by mutations in the FBN2 gene. The FBN2 gene provides instructions for producing the fibrillin-2 protein. Fibrillin-2 binds to other proteins and molecules to form threadlike filaments called microfibrils. Microfibrils become part of the fibers that provide strength and flexibility to connective tissue. Additionally, microfibrils hold molecules called growth factors and release them at the appropriate time to control the growth and repair of tissues and organs throughout the body. A mutation in the FBN2 gene can reduce the amount and/or quality of fibrillin-2 that is available to form microfibrils. As a result, decreased microfibril formation weakens the elastic fibers and allows growth factors to be released inappropriately, causing tall stature, deformities of the fingers and toes, and other characteristic features of congenital contractural arachnodactyly.