The exact cause of neural tube defects like spina bifida remains unknown. However, rather than being attributable to just a single cause, its occurrence is believed to be multifactorial. Spina bifida most likely results from the interaction of dozens of genes with both environmental and nutritional factors at play.
Genetic Risk Factors
The genetic factors implicated in causing spina bifida are complex and continually under investigation. Changes in genes involved in the processing of folic acid and changes in genes that are related to the formation of the neural tube contribute to spina bifida risk. The most conclusive evidence surrounds the gene methylenetetrahydrofolate reductase (MTHFR). The MTHFR gene is responsible for making an enzyme used in the processing of folic acid. MTHFR gene mutations may contribute to a shortage of folate during fetal development, a well-established contributory cause of neural tube defects.
There’s no clear pattern of genetic inheritance of spina bifida. However, a familial risk is present with affected first-degree relatives: a child's parents or siblings with spina bifida. Having an affected parent or sibling confers a two to five percent risk for the child. When two first-degree relatives are affected, the risk is subsequently doubled.
Nutritional Risk Factors
During the early months of pregnancy, a folate or vitamin B9 deficiency significantly increases the risk of spina bifida. It’s highly recommended that the diet of women of childbearing age be rich in folic acid, the synthetic form of folate found in fortified foods and provided in prenatal supplements. The incidence of neural tube defects can be reduced by approximately 70 percent when a pregnant woman's diet is supplemented with folic acid. In addition, in cases where spina bifida does occur, its severity has been shown to be greatly reduced with folic acid dietary supplementation.
Environmental Risk Factors
Environmental risk factors to the fetus that are associated with increased spina bifida incidence include elevated core maternal body temperature, certain medications, and some medical conditions.
Raised maternal core body temperature during the early weeks of pregnancy when the neural tube is being formed may increase the likelihood of spina bifida. Therefore, all pregnant women should avoid saunas and jacuzzis. In cases of fever, they should take pregnancy-safe antipyretics.
Anticonvulsant medications, in particular valproic acid, have been indicated in causing neural tube defects when taken during pregnancy. It is speculated that this is due to the anticonvulsant medications interfering with the body's ability to use folate properly.
Poorly managed diabetes and obesity are two medical conditions associated with spina bifida. Diabetic mothers with uncontrolled blood sugar levels have a higher risk of giving birth to a baby with a neural tube defect. Likewise, obesity that was preexistent to pregnancy is associated with an increased risk of spina bifida.
