Neural tube defect

Neural tube defect (NTDs) are one of the most common birth defects, occurring in approximately one in 1,000^[1] live births in the United States. An NTD is an opening in the spinal cord or brain that occurs very early in human development. In about the 3rd or 4th weeks of pregnancy, specialized cells in the dorsal region begin to fuse and curl up which rolls into a tube (the neural tube) after the baby is conceived. When the neural tube does not close completely, an NTD develops.

Types of NTDs

There are two types of NTDs.Open and Close NTDs. The most common type are called the Open NTDs. Open NTDs occur when the brain and/or spinal cord are exposed at birth through a defect in the skull or vertebrae (back bones). Examples of open NTDs are anencephaly, encephaloceles, hydranencephaly, iniencephaly, schizencephaly,and spina bifida. Rarer types of NTDs are called closed NTDs. Closed NTDs occur when the spinal defect is covered by skin. Common examples of closed NTDs are lipomyelomeningocele, lipomeningocele, and tethered cord.

Anencephaly

Anencephaly(without head) is a neural tube defect that occurs when the head end of the neural tube fails to close, usually during the 23rd and 26th days of pregnancy, resulting in a absence of a major portion of the brain and skull. Infants born with this condition are born with out the main part of the forebrain-the largest part of the cerebrum. Infants born with this condition are usually blind, deaf, and usually unconscious. The lack of a functioning cerebrum will ensure that the infant will never gain consciousness. Infants are either stillborn or usually die within a few hours or days after birth.

Encephaloceles

Encephaloceles are a neural tube defect that characterize by sac-like protrusion of the brain though through the opening in the skull. The defect is caused by the incomplete closure of the cranium during development.

Hydranencephaly

Hydranencephaly is a condition in which the cerebral hemispheres are missing and instead filled with sacs filled with cerebrospinal fluid.

Iniencephaly

This is a rare neural tube defect that result in extreme bending of the head to the spine. The diagnose can be made immediately after birth because the head is bend back and the face looks upward. Usually the neck is absent. The skin of the face connects directly to the chest and the scalp connect to the upper back. The infant usually will not survive more than a few hours.

Causes

Pregnant women taking medication for epilepsy have a higher chance of having a child with a neural tube defect. Research has shown that women with folic acid deficiencies also have a higher chance of having a child with a neural tube defect, but this is only one factor. Taking folic acid does not completely negate the risk of neural tube problems, but it does significantly reduce the risk. Folic acid deficiency leads to hyper-homocysteinemia,which in turn results in neural tube defects.^[2]

Folic acid pathway

Folic acid and vitamin B12 are very important in reducing the occurrences of NTDs. ^[3]

Other Causes

Other potential causes can include folate antimetabolites (such as methotrexate), maternal diabetes, maternal obesity, mycotoxins in contaminated corn meal, arsenic, and hyperthermia in early development^[4].^[5][6]

Prevention

In Canada, mandatory fortification of selected foods with folic acid has been shown to reduce the incidence of neural tube defects by 46%^[7].

Women who could become pregnant are advised to get 400 micrograms of folic acid daily. Women who are pregnant should receive 1.0 mg daily, and women who have previously given birth to a child with a neural tube defect should get 4.0 mg daily.^[8]

Detection

Neural tube defects may be detected by a variety of methods, including some prenatal screening tests and medical imaging. Often, these defects are apparent at birth, but occult defects may be not diagnosed until much later in life. Elevated levels of Alpha-fetoprotein (AFP) are seen in maternal blood or in the amniotic fluid when neural tube defects occur. Some authorities^[who?] recommend that non-pregnant women in child bearing age consume about 400 mcg of folic acid daily, and that pregnant women consume 800 mcg.

Treatment

See also

• Neurulation

References

1. ^ http://www.nichd.nih.gov/health/topics/neural_tube_defects.cfm/ through http://www.nichd.nih.gov.
2. ^ Mosley, B. S., Cleves, M. A., Siega-Riz, A. M., Shaw, G. M., Canfield, M. A., Waller, D. K., et al. (2009). Neural Tube Defects and Maternal Folate Intake Among Pregnancies Conceived After Folic Acid Fortification in the United States. [Article]. American Journal of Epidemiology, 169(1), 9-17.
3. ^ Molloy, A. M., Kirke, P. N., Troendle, J. F., Burke, H., Sutton, M., Brody, L. C., et al. (2009). Maternal Vitamin B-12 Status and Risk of Neural Tube Defects in a Population With High Neural Tube Defect Prevalence and No Folic Acid Fortification. [Article]. Pediatrics, 123(3), 917-923.
4. ^ eMedicine url=http://www.emedicine.com/NEURO/topic244.htm
5. ^ Suarez, L., Brender, J. D., Langlois, P. H., Zhan, F. B., & Moody, K. (2007). Maternal exposures to hazardous waste sites and industrial facilities and risk of neural tube defects in offspring. [Article]. Annals of Epidemiology, 17(10), 772-777.
6. ^ Zhou, F. C., Fang, Y., & Goodlett, C. (2008). Peptidergic agonists of activity-dependent neurotrophic factor protect against prenatal alcohol-induced neural tube defects and serotonin neuron loss. [Article]. Alcoholism-Clinical and Experimental Research, 32(8), 1361-1371.
7. ^ De Wals P, Tairou F, Van Allen MI, et al. (2007). "Reduction in neural-tube defects after folic acid fortification in Canada". N Engl J Med 357 (2): 135–142. doi:10.1056/NEJMoa067103. PMID 17625125. http://content.nejm.org/cgi/content/short/357/2/135?query=TOC. 
8. ^ Recommendations for the Use of Folic Acid... Accessed 22 Nov 2009.

External links

• MedlinePlus

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