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All About Arachnodactyly: The Strange Sign of Spider Fingers

written by: Leigh A. Zaykoski•edited by: Leigh A. Zaykoski•updated: 3/31/2010

Some rare genetic disorders cause arachnodactyly, also known as spider fingers. Learn about this symptom of rare genetic diseases and what you can expect.

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    Description

    Arachnodactyly presents as long, slender, and curved fingers that resemble the legs of a spider, hence the more common name of “spider fingers." While slender, long fingers may be normal, they can also signal an underlying genetic disorder.

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    Causes

    Homocysteinuria

    Homocystinuria causes an inability to process amino acids properly. This genetic disorder has several forms, with the most common form resulting from a lack of the enzyme cystathionine beta-synthase. This form of the condition causes dislocation of the lens of the eye, skeletal abnormalities and an increased risk of blood clots. In some cases, children with this form of the disorder have learning difficulties and developmental delays. Other forms of homocystinuria result from a lack of other enzymes needed to process amino acids. These forms of the disorder cause seizures, movement problems, megaloblastic anemia and learning disabilities.

    Homocystinuria results from mutations in the MTHFR, CBS, MTRR, and MTR genes. The CBS gene mutation disrupts the function of cystathionine beta-synthase in the body. This causes homocysteine levels to increase. The body excretes the excess in the urine, leading to elevated urine levels of homocysteine. The MTHFR, MTRR, and MTR genes help the body convert homocysteine to methionine. When mutations occur in these genes, the enzymes do not function properly. This results in elevated homocysteine levels.

    Marfan Syndrome

    Marfan syndrome is a connective tissue disorder that affects many parts of the body. Since connective tissues support the cartilage, ligaments, tendons and walls of the blood vessels, this disorder causes several problems. This condition results in an abnormal makeup of connective tissue, which means many structures do not have the stiffness necessary for proper function. Two of the most serious problems associated with Marfan syndrome are cardiac valve and blood vessel problems.

    When the connective tissues in the heart are not strong enough, blood can leak backward through the aortic and mitral valves. This makes the heart work harder and can lead to enlargement of the heart muscle. Marfan syndrome also causes the walls of the major arteries to weaken. When the aorta weakens, it dilates, weakening the inner wall of the aorta. This increases the risk of an aortic tear, which allows blood to leak through the tear and separate the walls of an aorta. Marfan syndrome also increases the risk for an aortic aneurysm.

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    Seeking Medical Care

    When you visit your child’s doctor to discuss arachnodactyly, you should be prepared to answer several questions. The National Institutes of Health reports that your doctor will ask you when you first noticed the shape of your child’s fingers, whether any other symptoms are present and if there is a family history of genetic disorders. If your doctor suspects a hereditary disorder, he may order diagnostic tests to find out if one exists. The treatment plan for your child will depend on the underlying cause of the arachnodactyly.

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    References

    National Institutes of Health: Arachnodactyly

    Genetics Home Reference: Homocysteinuria

    American Heart Association: Marfan Syndrome