Spina bifida is a birth defect where a baby’s spine and spinal cord do not form properly during early pregnancy. It is a type of neural tube defect, which are conditions affecting the brain and spinal cord, resulting from the incomplete closure of the neural tube—the embryonic structure that forms the brain and spinal cord. This typically develops within the first 28 days after conception. The severity of spina bifida can vary significantly, ranging from mild, hidden forms to more severe types that involve the protrusion of spinal nerves. Its causes are complex, involving an interplay of various factors.
Understanding the Genetic Connection
Spina bifida is not typically inherited in a simple, predictable pattern like some single-gene disorders, but genetics do play a role in a person’s risk. It is considered a multifactorial condition, meaning that both genetic predispositions and environmental factors contribute to its development. While most cases occur sporadically, having a first-degree relative with spina bifida can increase the risk. However, the majority of babies born with spina bifida do not have parents with a known family history of the defect.
The genetic component is estimated to contribute around 60-70% to the risk of spina bifida. The inheritance pattern is often described as involving “liability genes,” where a combination of multiple genetic variations increases susceptibility. This complex genetic background means that no single gene is solely responsible for causing spina bifida in most instances.
How Genes Contribute to Spina Bifida
The genetic influence on spina bifida involves multiple genes, each contributing a small part to the overall risk. Researchers have identified variations in dozens of genes that may affect an individual’s susceptibility. A prominent example is the MTHFR gene, which provides instructions for a protein involved in processing folate, a B vitamin. Variations in this gene can impair the body’s ability to metabolize folate effectively, thereby increasing the risk of neural tube defects.
Other genes linked to spina bifida include those involved in the development of the neural tube itself. Genes such as VANGL1, VANGL2, FUZ, CELSR1, and TBXT have been associated with the condition, with studies indicating their potential role in neural tube closure. These genetic variants can affect cellular signaling pathways and processes critical for proper embryonic development. The current understanding points towards an “omnigenic model,” suggesting that spina bifida arises from a series of genetic variants.
Beyond Genetics: Other Influences
Beyond genetic factors, several environmental influences play a significant role in the development of spina bifida, reinforcing its multifactorial nature. The most widely recognized environmental factor is insufficient maternal folic acid intake before and during early pregnancy. Folic acid, a synthetic form of folate (vitamin B9), is essential for healthy cell division and neural tube formation. A deficiency can significantly increase the risk of spina bifida and other neural tube defects.
Certain medications taken during pregnancy can also increase the risk. Anti-seizure drugs like valproic acid, carbamazepine, and topiramate have been linked to a higher incidence of spina bifida, potentially by interfering with folate utilization. Additionally, maternal health conditions such as uncontrolled diabetes before pregnancy and obesity are recognized risk factors. Increased body temperature in early pregnancy, from fever or sources like hot tubs, has also been suggested as a potential influence.
Steps for Risk Reduction
Preventive measures primarily focus on ensuring adequate folic acid intake for individuals who could become pregnant. The U.S. Public Health Service recommends that all individuals capable of becoming pregnant consume 400 micrograms (0.4 mg) of folic acid daily. This supplementation should begin at least one month before conception and continue through the first three months of pregnancy, as the neural tube closes very early in development. Studies indicate that consistent folic acid supplementation can reduce the risk of neural tube defects by up to 70%.
For individuals with a higher risk, such as those with a family history of neural tube defects or a previous pregnancy affected by spina bifida, a higher dose of 4000 micrograms (4.0 mg) of folic acid per day is often recommended, requiring a prescription. A balanced diet rich in natural folate, found in foods like leafy green vegetables, citrus fruits, and fortified cereals, supports overall health, though supplements are crucial for meeting prevention guidelines. Managing pre-existing health conditions, such as diabetes and obesity, before and during pregnancy can also help reduce risks. Genetic counseling offers a valuable resource for individuals with a family history of neural tube defects, providing information on recurrence risks, genetic testing options, and preventive strategies.