Spina bifida is a birth defect affecting the spinal cord, occurring when the neural tube, which forms the early brain and spinal cord, does not close completely during early pregnancy. This condition can lead to varying degrees of physical and intellectual disabilities, depending on the defect’s severity and location. While genetics contribute, spina bifida is a complex condition influenced by multiple interacting factors, including environmental influences. This interplay of genetic predisposition and external elements determines an individual’s susceptibility.
Genetic Factors in Spina Bifida
Spina bifida does not typically follow a simple inheritance pattern where a single gene dictates the trait. Instead, it is considered a multifactorial or polygenic condition, meaning that multiple genes interact with each other and environmental factors to increase susceptibility. Researchers have identified several genes that may play a role in neural tube development, though no single gene has been pinpointed as the sole cause. These genes are thought to influence processes like folate metabolism and cell signaling pathways, which are important for proper spinal cord formation.
The genetic contribution means that families with one child affected by spina bifida have a slightly increased chance of having another child with the condition compared to the general population. While the general population risk is about 0.05% to 0.1% (or 0.5 to 1 per 1,000 births), the recurrence risk for a second child can range from approximately 2% to 5%. This elevated risk highlights a genetic predisposition, but it also underscores that genetics alone do not guarantee the condition’s recurrence. Environmental factors also play a role.
Environmental Factors and Risk Reduction
Folic acid deficiency is the most significant environmental risk factor identified for spina bifida and other neural tube defects. Folic acid, a B vitamin, is necessary for the rapid cell division and tissue development that occurs in the earliest stages of pregnancy. It plays a direct role in the formation and closure of the neural tube, which typically happens within the first 28 days after conception, often before a woman knows she is pregnant. Adequate folic acid levels help ensure this developmental process proceeds without complications.
Health organizations recommend that all women of childbearing age consume 400 micrograms (mcg) of folic acid daily. This supplementation should begin at least one month before conception and continue through the first three months of pregnancy. For women who have previously had a pregnancy affected by a neural tube defect, a higher dose of 4,000 mcg (4 milligrams) per day is often recommended, starting one month before conception and continuing through the first trimester. While folic acid supplementation can reduce the risk by up to 70%, it cannot eliminate it entirely, indicating the presence of other contributing factors.
Beyond folic acid, other environmental factors can influence the risk of spina bifida. Certain medications, such as some anti-seizure drugs, have been associated with an increased risk if taken during early pregnancy. Pre-existing medical conditions in the mother, such as uncontrolled diabetes or obesity, have also been linked to a higher incidence of neural tube defects. Managing these health conditions and discussing all medications with a healthcare provider before and during pregnancy can contribute to risk reduction.
Recognizing Types of Spina Bifida
Spina bifida presents in various forms, differing in severity and the extent of spinal cord involvement.
Myelomeningocele
Myelomeningocele is the most common and severe type of spina bifida. In this form, a sac containing parts of the spinal cord, nerves, and cerebrospinal fluid protrudes through an opening in the back. This exposure and damage to the spinal cord and nerves often lead to varying degrees of paralysis below the level of the defect, as well as bladder and bowel control issues and sometimes hydrocephalus.
Meningocele
Meningocele is a less common and less severe type of spina bifida. With meningocele, a sac of fluid protrudes through an opening in the back, but it contains only meninges, the protective membranes surrounding the spinal cord, and no nerve tissue. Because the spinal cord itself is not directly involved or damaged, individuals with meningocele often experience minimal to no nerve damage or disability. The primary concern is usually the surgical closure of the sac to prevent infection.
Spina Bifida Occulta
Spina Bifida Occulta represents the mildest form of the condition and is often asymptomatic, meaning many individuals may not even know they have it. In spina bifida occulta, there is a small gap in one or more vertebrae, but the spinal cord and its membranes do not protrude through the opening. The defect is covered by skin, sometimes marked by a dimple, a tuft of hair, or a discoloration on the lower back. It is often discovered incidentally during imaging for other medical reasons and rarely causes significant problems.