About 2 to 3 percent of people in this country have intellectual disabilities, and in many cases, the cause is unknown. A new study by March of Dimes grantee Scott Soderling at Duke University in Durham, North Carolina, shows how one gene may contribute to intellectual disabilities.
There are probably hundreds of different causes of intellectual disabilities. Some known causes include chromosomal abnormalities, such as Down syndrome, and single-gene disorders, such as fragile X syndrome. Even though scientists have pinpointed the genes that cause several forms of intellectual disabilities, they don’t fully understand how the abnormal genes affect the workings of the brain. “It is impossible to correct something without knowing what the exact underlying problem is,” says Dr. Soderling.
Dr. Soderling set out to determine how a gene called WRP, which has been linked with serious intellectual disabilities, affects brain development. His study showed that WRP regulates how nerve cells in the developing brain form connections called synapses with other nerve cells. Nerve cells in a lab dish enriched with WRP formed many finger-like projections, which the cells need to form connections. Cells lacking WRP made fewer projections, which could lead to fewer synapses.
How does this affect brain function? Nerve cells in the brain communicate with each other by passing electrical signals across synapses. Abnormalities in the number or structure of synapses can interfere with communication between nerve cells and may contribute to intellectual disabilities. Dr. Soderling found that mice lacking the WRP gene fared poorly on tests of learning and memory, suggesting that abnormalities in the human version of the gene could have similar effects. Other genes besides WRP, including the fragile X gene, also may affect synapses.
Special education programs help children with intellectual disabilities reach their full potential. However, there is no effective treatment for these disorders. Dr. Soderling’s study provides hope that this could change. “Because the types of synapses we are studying form their connections right after birth in humans, we think there may be an opportunity for early intervention after birth,” said Dr. Soderling.
Most birth defects cannot be prevented because their causes are not known. However, women can take a number of steps before and during pregnancy to reduce their risk [link to Birth Defects fact sheet]. These steps include taking a multivitamin containing 400 micrograms of folic acid daily starting before pregnancy and in early pregnancy. This helps to prevent serious birth defects of the brain and spinal cord, including spina bifida, and may also help prevent heart defects.
Congenital heart defects are among the most common birth defects, affecting nearly 1 out of 100 babies in the United States. Some heart defects are mild, while others can be life-threatening. Other common birth defects include cleft lip/palate, Down syndrome and spina bifida (open spine), affecting about 1 in 700, 1 in 800 and 1 in 2,500 babies respectively.
Environmental substances that can contribute to birth defects include alcohol, certain drugs/medications and infections. Women who drink heavily during pregnancy are at risk of having a baby with a pattern of mental and physical birth defects called fetal alcohol syndrome. Because even moderate or light drinking may harm a baby, women who are pregnant or planning pregnancy should not drink any alcohol. They also should avoid illegal drugs such as cocaine and Ecstasy, and ask their health care provider about the safety of any prescription and over-the-counter medications they take. Women also can take steps to help prevent certain infections such as toxoplasmosis and cytomegalovirus that can cause birth defects.