What are they?
Neural tube defects (NTDs) are a group of disorders that arise early in fetal development and can cause life-long complications of varying severity. During the first 3-4 weeks of development, specific cells in an embryo curl up and their edges fuse together to form a narrow tube that becomes the foundation of the spinal cord, brain, and the bone and tissues that surround it. This neural tube fusing process usually is complete by 28 days of gestation – before many women even know that they are pregnant. If the tube does not close properly along its entire length, then a NTD will form at the open location.
Normally, the spinal cord and brain are surrounded and cushioned by cerebrospinal fluid (CSF) and are protected by outer layers of tissue called the meninges. The brain is further protected by the skull, and the spinal cord is protected by the vertebrae, which form a flexible protective armour of bone. When someone has a NTD, there are one or more gaps in the brain or spinal cord’s protection. This can affect the brain’s development and can leave the spinal cord vulnerable to damage. Because the spinal cord contains the nerves that control body movement, any damage that occurs can paralyse or weaken associated muscles and organs. The type of NTD that develops, its severity, its affect on fetal development, and its potential for future complications will depend upon where the opening is and what tissues are involved.
The cause of NTDs is not known. Scientists believe that there are genetic, environmental, and nutritional components. The parents of about 95% of babies born with NTDs do not have a family history of these disorders. Some seizure medications, such as valproic acid and carbamazepine, have been associated with an increased risk, as have certain diseases in the mother, such as diabetes. Risk can be reduced but not eliminated by ensuring that the mother has adequate folate/folic acid at the time of conception (for more on this see Treatment).
Spina bifida, also called spinal dysraphism, is the most common type of NTD. According to the Australian Spina Bifida and Hydrocephalus Association, spina bifida affects about 1 in 1600 pregnancies in Australia. It occurs when the neural tube does not close completely somewhere along the spine. Symptoms vary from person to person and can change over time. They tend to occur below the defect and may range from few or none, to partial or total lower body weakness, loss of feeling, or paralysis. Complications will also vary. About 80%-90% of people with severe spina bifida will have hydrocephalus and 90% of these will need surgery to insert a shunt shortly after birth. Many children who have hydrocephalus will have some learning disabilities. Physical complications may include Chiari malformation or hydrocephalus (see Types) gastrointestinal disorders, urinary and bowel dysfunction, obesity, depression, tendonitis, and an increased tendency towards latex allergies.