The gene that may contribute to intellectual disabilities

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.