Spina Bifida and Genetics

What causes spina bifida? The answer can be found early on in embryo development when the nervous system starts to form. A small section of cells along the back of an embryo will create the neural tube. This is a narrow section of nervous tissue that will in the end form the child's nervous system, including the brain and the spinal cord. Sometimes defects occur in this process of embryo maturation creating faults in the neural tube. These are called neural tube defects, and can be devastating for the health and physical development of the child.

Spina bifida can be defined as an incomplete development of the brain, spinal cord, and/or meninges. According to the National Institute of Neurological Disorders and Stroke (2008) spina bifida is the most common neural tube defect in the United States—affecting 1,500 to 2,000 of the more than 4 million babies born in the country each year.

There are three main types of spina bifida;

Occulta - this is the most common, but also the mildest form of the disease - there's a malformation on one or more vertebrae. The malformation is "hidden" since the defect in the spine is covered by a layer of skin. Occulta rarely causes disability in the patient.

Meningocele - causes the meninges to protrude from a spinal opening. Symptoms vary from patient to patient.

Myelomeningocele - the most severe type of disease and it occurs when the spinal cord is exposed through an opening in the spinal canal. Children born with this defect have partial or complete paralysis of the body below the spinal opening. The paralysis may be severe with urinary and bowel dysfunction.

To this day the causes of spina bifida are unknown. It is believed that a combination of genetic and environmental causes are at the root of this birth defect.

There is a body of research on the possible genetic causes of spina bifida. Scientists from The University of Texas Medical School at Houston discovered an association between genes regulating glucose metabolism (the way the body uses its major fuel, glucose) and spina bifida. The study lasted 10 years and involved more than 1,500 DNA samples from parents and children with spina bifida birth defects. The overall goal of this study was to identify variations in genes of glucose metabolism that are important in the process of spine formation. High glucose levels have long been thought of as a contributory factor to the development of spina bifida.

More specifically, DNA sequencing was performed on more than 500 children with spina bifida and on their parents, and a control group. The study found a significant association between Lys481 of HK1 (G allele), Arg109Lys of LEPR (G allele), and Pro196 of GLUT1 (A allele). Three single nucleotide pairs on 3 genes involved with glucose metabolism and obesity may be associated with increased susceptibility to spina bifida development.

Research also indicates that insufficient intake of folic acid—a common B vitamin—by the mother is an important factor in causing spina bifida and other neural tube defects. Prenatal vitamins are often prescribed to pregnant women to prevent spina bifida and other birth defects.

Unfortunately, there is no cure for spina bifida. Damage to nerve tissue cannot be repaired or replaced. Its lost function cannot be restored. Treatment options for people with spina bifida depends on the type and severity of the disorder. Children with the mild form may need no treatment. Some may require surgery when they are older.

National Institute of Neurological Disorders and Stroke (2008) (http://www.ninds.nih.gov/disorders/spina_bifida/detail_spina_bifida.htm)

Christina M. Davidson, Hope Northrup, Terri M. King, Jack M. Fletcher, Irene Townsend, Gayle H. Tyerman, and Kit Sing Au (2008). Genes in Glucose Metabolism and Association With Spina Bifida. Reproductive Sciences, Jan 2008; vol. 15: pp. 51 - 58. (http://rsx.sagepub.com/cgi/content/abstract/15/1/51)