What is Neural Tube Disorders?
Neural tube defects (NTDs) are congenital abnormalities (i.e., present at birth) that affect the brain and spinal cord. They are the most common severe abnormalities of the central nervous system, next to cardiovascular defects, and can lead to serious health issues and sometimes even death. The brain and spinal cord develop from the ectoderm, which is one of the three primary layers of cells in an embryo. They form through a process called neurulation, which begins only 3 to 4 weeks after conception. This process involves the folding of neural plates, a critical part of an embryo’s development into a complex organism.
If neurulation doesn’t go as planned, neural tube defects can occur. Neurulation actually involves two stages – primary and secondary. Primary neurulation is the folding and lengthening of neural plates, which eventually form the brain and spinal cord. Secondary neurulation then forms the lower part of the spinal cord.
The growth factor FGF assists in the formation of the neural plate, which is a precursor to the nervous system. Additionally, retinoic acid, a form of Vitamin A, also aids this process by regulating the expression of certain genes.
Depending on where the failure in closing occurred, neural tube defects can be present anywhere in the nervous system, from the brain to the end of the spinal cord. Open NTDs occur when there’s a failure during primary neurulation, and oftentimes lead to issues such as fluid on the brain (hydrocephalus) and certain malformations. On the other hand, closed NTDs, which result from issues in secondary neurulation, typically only affect the spinal cord and do not expose any neural tissue.
The most common types of NTDs include: Spina bifida occulta, where the spinal cord and its protective covering, the meninges, stay intact; Spina bifida cystica, which involves the herniation, or protrusion, of meninges, and sometimes the spinal cord too; Myeloschisis, where neural tissue is exposed without any covering; Anencephaly, where the brain and skull are severely malformed due to the failure of rostral neuropore closure, a critical part of brain development.
What Causes Neural Tube Disorders?
Neural tube defects, or problems in the brain and spinal cord’s development, can be influenced by a mix of genetic influences and environmental factors. Many things can play a part in these defects, like a person’s weight, whether they have diabetes, how their immune system functions, use of certain drugs, their socioeconomic status, where they live, and their ethnic background. It’s important to note that we don’t fully understand how location and ethnicity factor into these conditions yet, but we do know that these defects can vary from place to place.
People with lower incomes might not have easy access to folic acid supplements during pregnancy, and these important supplements are known to help prevent neural tube defects.
Several other factors could also contribute to neural tube defects. Certain conditions in the womb, such as amniotic bands (fibrous string-like tissue), can disrupt the tube’s development. Some medications and high temperatures during pregnancy could also be potential risk factors.
Finally, the physical and chemical environment around a person could also contribute to these defects. Factors like radiation exposure, stress, high levels of vitamin A, infections like rubella, toxoplasmosis, and cytomegalovirus, and even toxic waste from landfills located within about 2 miles, all have the potential to increase the risk of neural tube defects to some extent.
Risk Factors and Frequency for Neural Tube Disorders
Neural tube defects (NTD) rates vary among different ethnicities, geographical locations, gender, and countries. It’s been observed that Whites have a higher prevalence compared to Blacks, and women compared to men. Southeast Asia reports a higher rate of these defects compared to western countries, which could be due to the lower economic status in the east affecting access to multivitamins like folic acid. Even within a single country, the rates can vary significantly, which is seen in countries with diverse lifestyles and economic statuses.
- According to data from January 1990 to July 2014, the eastern Mediterranean region showed a lot of variability, with Pakistan ranging from 38.6 to 124.1 cases per 10,000 births.
- In the African region, rates range from 5.2 to 75.4 per 10,000 births.
- In Europe, it ranges from 1.3 to 35.9 per 10,000 births.
- In the Americas, it’s from 1.4 to 27.9 cases per 10,000 births.
These variations from place to place are thought to be due to differences in healthcare facilities, although the exact mechanism is still unknown. NTDs have been found to be more common in twins and especially identical twins compared to single births. Different types of these defects also vary, with a study in Los Angeles showing a higher rate of anencephaly and exencephaly compared to spina bifida. It has also been noted that the chances of stillbirth are higher in female offspring, whereas the chances of miscarriage are higher in males. Overall, Neural tube defects occur in 1 to 2 out of every 1000 births.
Signs and Symptoms of Neural Tube Disorders
Neural Tube Defects (NTDs) are health conditions that can affect women of childbearing age. These women often come from lower socioeconomic backgrounds and may lack proper folic acid supplementation during their pregnancy. Other factors may include a family history of NTDs, experiencing weakness or fatigue, having anemia, diabetes, or using epilepsy medication.
Healthcare professionals can diagnose NTDs both before and after the baby is born, usually via ultrasound screenings. Some NTDs can even be discovered later in childhood or adulthood. NTDs often include anencephaly, which is a severe condition that can be diagnosed more easily before birth. Alongside NTDs, patients may also experience urinary problems, neurological weakness, and heart-related complaints.
The physical signs of NTDs vary depending on the size and type of the defect. Open NTDs are usually easy to spot, while closed ones may require more effort to detect. A newborn with an NTD might also have a low birth weight or other physical anomalies such as a cleft palate, undescended testis, or a deformity of the foot known as talipes. Around a third of NTD cases coincide with these additional physical anomalies.
A larger than normal head size due to fluid buildup can also indicate NTDs. So can closed spinal defects associated with certain conditions like lipomyelocele and lipomeningomyelocele, or rare features like a dorsal enteric fistula, anal imperforation, cardiac and kidney abnormalities, a tuft of hair, and spinal curvature. In some cases, a sac-like structure filled with spinal fluid may be present. Cognitive impairment and delayed walking may also be signs of NTDs. In addition, mothers of children with NTDs may appear pale and anemic.
Testing for Neural Tube Disorders
Ultrasound is a commonly used tool in prenatal screening. It can provide clear details about the size and location of any neural tube defects and issues with the spine in an unborn baby. The accuracy of the diagnosis using ultrasound largely depends on how far along the pregnancy is, and a careful examination of any anomalies.
Alpha-fetoprotein is a protein produced by the baby’s yolk sac, liver, and digestive system. Initially, this protein is found in higher levels in the amniotic fluid and fetal plasma than in the mother’s blood. However, as the pregnancy progresses and the placenta becomes more permeable, the alpha-fetoprotein can cross over to the mother’s blood. So, the concentration of alpha-fetoprotein in the mother’s blood increases while decreasing in the amniotic fluid and fetal plasma. Elevated levels of alpha-fetoprotein can be a sign of neural tube defects. If this protein is detected in high levels, the level of another enzyme, acetylcholinesterase, is also checked. Despite alpha-fetoprotein’s crucial role in screening for neural tube defects, this approach is not cost-effective.
Magnetic Resonance Imaging (MRI) is another imaging tool that is used when the ultrasound results are not clear enough to make an accurate assessment of the baby’s condition. Although MRI is helpful in diagnosing neural tube defects, some studies in chicks have suggested that exposure to MRI might increase the incidence of these disorders.
Chromosomal Microarray is a genetic testing method used to assess the link between genetic mutation and neural tube defects. This is because it’s known that neural tube disorders can be linked to genetic abnormalities.
In many instances, neural tube defects can co-exist with other abnormalities such as heart defects, cleft palate, urinary tract infections, and coloboma, which is an eye condition.
Checking the level of folic acid in the mother’s blood before or during pregnancy can help identify potential causes of neural tube defects.
Treatment Options for Neural Tube Disorders
Taking folic acid supplements before and during pregnancy can significantly reduce the risk (by 50% to 70%) of developing neural tube disorders in babies. These disorders affect the baby’s brain and spine. It is advised that women who wish to become pregnant take 0.4 to 0.8 mg of folic acid every day. However, if a woman has had a baby with a neural tube disorder before or has a family history of this, then a larger dose of 4 mg of folic acid is recommended from a month before conception until three months into the pregnancy. It’s generally a good idea to start taking folic acid 5 to 6 months before becoming pregnant to best prevent these disorders.
If a baby has myelomeningocele, a type of spina bifida where the spinal cord sticks out through an opening in the spine, it can be treated through surgery while still in the womb. This surgery helps stop any leakage of spinal fluid, preventing further complications like herniation of the cerebellum and the build-up of fluid in the brain known as hydrocephalus. If the surgery isn’t carried out before the baby is born, it should ideally be done within 72 hours after birth. Several studies have shown that babies who have this surgery before they are born may have better mobility and cognitive abilities. There is also data suggesting that having this surgery before birth may improve bladder function.
If a baby is born with hydrocephalus, a condition where there is too much fluid in the brain, it can be treated by implanting a device known as a ventriculoperitoneal shunt. This shunt helps drain the fluid from the brain to the belly area.
Fever-reducing medications, also known as antipyretics, can help lower the chances of a baby developing neural tube disorders.
Upon a doctor’s confirmation that a baby is likely to be born with a neural tube disorder, the mother and family should receive information about what the disorder is, how it can be managed, the possible outcomes, and how various healthcare professionals can support them through this period.
Managing diabetes during pregnancy is important as it can reduce the chances of a baby developing neural tube disorders.
If babies are born with neural tube defects and have not been diagnosed before birth, doctors will check for any leakage of spinal fluid, infections, or any other sign of the disorder and give appropriate treatment. The babies should be examined with clean procedures using non-latex gloves to reduce the risk of allergies. Antibiotics may also be given to prevent infections. Closing the neural tube surgically after birth may be complex and needs careful planning to reduce the risk of complications.
What else can Neural Tube Disorders be?
Neural tube disorders can be categorized based on their location, outer covering, and what’s inside them. It’s crucial to distinguish these types for the right treatment approach. Neural tube defects can either start in the spinal cord or the brain, and could be either open or closed. The open types include myelomeningocele, hemimyelocele and lipomyelomeningocele. Closed types, on the other hand, could be meningocele, lipomyelocele, and others. There’s also a condition called anencephaly.
Here’s more on some other conditions related to neural tube disorders:
- Iniencephaly: This is a rare, fatal condition linked with abnormalities like spina bifida, heart defects, cleft palate, and abnormal kidneys. You can typically tell this apart from neural tube defects by the involvement of the thoracic spine, missing ribs, and kyphosis (a type of curve in the spine).
- Meckel-Gruber Syndrome: This is a condition that runs in families, and involves a group of disorders related to dysfunctional tiny hair-like structures called cilia. Neural tube defects are part of this syndrome, along with issues in other parts of the body where cilia play a key role. This includes the respiratory tract, certain reproductive and urinary ducts, and brain ventricles. If you notice symptoms like respiratory disease, infertility, polycystic kidney disease and increased fluid in the brain (hydrocephalus), this can help differentiate this syndrome from regular neural tube disorders.
- Tethered Cord Syndrome: This occurs when the spinal cord is abnormally stretched, usually due to benign growths like a lipoma or a dermoid cyst.
- Viral and Neonatal Meningitis: These can cause premature births, and symptoms like neck stiffness and fever, which may be mistaken for meningitis in patients with neural tube defects.
- Lipomyelomeningocele: This is a type of growth made of fatty tissue that attaches to surrounding soft tissue, leading to the spinal cord being pulled down, which affects neurological functions. Its presence, especially in the upper spine and neck region, can cause confusion with other neural tube defects.
- Myelocystocele: This is a type of closed neural tube defect that looks similar to a myelomeningocele, especially when it’s complicated by the presence of water in the scrotum (hydrocele).
- Neurenteric Cyst: This develops due to an abnormal connection between two early embryonic cell layers and can sometimes be found in the brain and spinal cord, superficially looking like neural tube defects.
- Persistence of Terminal Ventricle: This rare condition appears as a cavity at the lower end of the spinal cord, and can be seen on radiological tests.
Overall, each of these conditions and syndromes can mimic neural tube defects, so it’s essential for these to be ruled out in the diagnosis process.
What to expect with Neural Tube Disorders
Advancements in prenatal screening have vastly improved how we handle neural tube defects – abnormalities that affects the brain and spine in growing babies. These advancements help doctors diagnose and intervene earlier, which has greatly minimized complications after birth and extended lifespans.
One key detail that impacts how severe these defects can be is the “level of disorder” and how much space it covers. Basically, if the problem is located higher up in the spine, and if it affects a larger area, the issues tend to be more serious. This can lead to the person being unable to walk on their own, difficulties with swallowing, and more use of a wheelchair.
Studies show that fixing the problem before birth typically results in better outcomes in terms of the person’s ability to walk, their cognitive functions, and other nervous system functions compared to if the operation happened after birth.
It’s important to note that if the person has other birth defects along with a neural tube defect, their odds of survival and risk of complications can increase.
Possible Complications When Diagnosed with Neural Tube Disorders
One of the severe complications of Neural Tube Defects (NTDs) includes stillbirths and premature labor that can lead to abortion.
- Polyhydramnios: This condition typically happens in babies with anencephaly as they can’t swallow the amniotic fluid, causing it to accumulate. It occurs in people with neural tube disorders and can slow down mental development. An estimated 27% of pregnancies with anencephaly develop this condition, and it generally develops in the second and third trimesters in about 50% of patients.
- Arnold-Chiari Malformation: It’s a disease that causes part of the brain (cerebellum) to fall into the area where the spinal cord enters the skull (foramen magnum) because of unusual spinal cord development due to spina bifida.
- Hydrocephalus: Brain malformation can lead to hydrocephalus, a condition where excess fluid builds up in the ventricles (cavities) of the brain. It’s related to a type of neural tube defect known as encephalocele.
- Meningitis: Children with NTDs are susceptible to meningitis, an infection of the membranes surrounding the brain and spinal cord, due to ongoing leakage of cerebrospinal fluid.
- Cognitive disability: Normal pressure, concentration and makeup of cerebrospinal fluid are essential for appropriate brain development, particularly the cerebral cortex. Patients with NTDs often have less cortical development, contributing to cognitive disability.
- Spinal fistula: In some instances, a spinal fistula, which is an abnormal connection involving the spine, can form, leading to continuous cerebrospinal fluid discharge.
- Complications from fetal surgery: Premature delivery, maternal complications, and fluid build-up in the lungs may occur. Different types of fetal surgeries carry unique risks. For example, preterm birth and a torn placenta are more common with minimally invasive surgery (percutaneous fetoscopic surgery), whereas a weakened uterine wall is more common with open surgery.
Preventing Neural Tube Disorders
Neural tube defects (NTDs), which are birth defects that can affect the brain, spine, or spinal cord in newborns, can be prevented in most situations. A community’s lack of involvement in promoting awareness of comprehensive health care, proper diet, prenatal testing, and cleanliness can result in these defects and other birth deformities. Consuming the right amount of a vitamin known as folic acid can reduce the chances of having babies with NTDs. Other supplements like methionine and inositol can also help reduce the odds if folic is not enough.
It’s also necessary for women who are taking medicines to control seizures to try to reduce their dosage as much as possible. These women may need to take a higher amount of folic acid to compensate for the interference of their seizure medicine. Blood tests, usually done around the fourth month of pregnancy, are highly recommended. With the help of an Ultrasound, doctors should vigilantly monitor all pregnant women, especially those who have reasons for concern, a family history or live in areas where these deformities are common.
If a problem is detected, prenatal surgery can often correct it and lead to good outcomes. The whole process would involve genetic counseling which means, healthcare professionals will explain to the family the nature and progression of the disease, potential complications, treatment procedures and the possible outcome. The process does not stop there; a regular follow-up over time is crucial regardless of initial treatment.
