lunes, 22 de octubre de 2012

Spina bifida - Genetics Home Reference

Spina bifida - Genetics Home Reference

Spina bifida
Reviewed February 2011

What is spina bifida?

Spina bifida is a condition in which the bones of the spinal column do not close completely around the developing nerves of the spinal cord. As a result, part of the spinal cord may stick out through an opening in the spine, leading to permanent nerve damage. Spina bifida results when a structure called the neural tube fails to close completely during the first few weeks of embryonic development. The neural tube is a layer of cells that ultimately develops into the brain and spinal cord. Because spina bifida is caused by abnormalities of the neural tube, it is classified as a neural tube defect (NTD).
Children born with spina bifida often have a fluid-filled sac on their back covered by skin. If the sac contains part of the spinal cord and its protective covering, the abnormality is known as a myelomeningocele. If it does not, the abnormality is known as a meningocele. The signs and symptoms of these abnormalities range from mild to severe, depending on where the opening in the spinal column is located and how much of the spinal cord is affected. Related problems can include a loss of feeling below the level of the opening, weakness or paralysis of the feet or legs, and problems with bladder and bowel control. Some affected individuals have additional complications, including a buildup of excess fluid around the brain (hydrocephalus) and learning problems. With surgery and other forms of treatment, many people with spina bifida live into adulthood.
There is also a milder form of the condition called spina bifida occulta, in which the spinal column is abnormal but the nerves of the spinal cord do not stick out through an opening in the spine. Spina bifida occulta usually causes no health problems, although rarely it can cause back pain or changes in bladder function.

How common is spina bifida?

Spina bifida is one of the most common types of neural tube defect, affecting an estimated 1 in 2,500 newborns worldwide. The prevalence of spina bifida varies among different geographic regions and ethnic groups. In the United States, this condition occurs more frequently in Hispanics and non-Hispanic whites than in African Americans.

What genes are related to spina bifida?

Spina bifida is a complex condition that is likely caused by the interaction of multiple genetic and environmental factors. Some of these factors have been identified, but many remain unknown.
Changes in dozens of genes may influence the risk of spina bifida. The best-studied of these genes is MTHFR, which provides instructions for making a protein that is involved in processing the B-vitamin folate (also called folic acid or vitamin B9). Changes in other genes related to folate processing and genes involved in the development of the neural tube have also been studied as potential risk factors for spina bifida. However, none of these genes appears to play a major role in causing the condition.
Researchers have also examined environmental factors that could contribute to the risk of spina bifida. A shortage (deficiency) of folate appears to play a significant role. Studies have shown that women who take supplements containing this vitamin before they get pregnant and very early in their pregnancy are significantly less likely to have a baby with spina bifida or a related neural tube defect. Other possible risk factors for spina bifida include diabetes mellitus, obesity, exposure to high heat (such as a fever or use of a hot tub or sauna) in early pregnancy, and the use of certain anti-seizure medications during pregnancy. However, it is unclear how these factors may influence the risk of spina bifida.
Read more about the MTHFR gene.

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