Neural Tube Defects from Even One Gene
Background: Neural tube defects (NTDs) are common birth defects of the brain and spinal cord that include anencephaly and spina bifida (meningomyelocele). Deficiency of the vitamin folic acid raises the risk of NTDs, as does mutation of a gene for an enzyme that processes folic acid. The mutation is called the C677T variant, or T for short.
Summary: People with two copies of the T mutation are two and a half times as likely to have a NTD as people with two copies of the normal gene. Now it has been found that people with just one copy of the T gene are also at increased risk for an NTD. They are one and a half times more likely to have a NTD than people with two copies of the normal gene.
Comments: NTDs provide a model of how the environment and genetics can interact to cause birth defects. The environmental factor is a lack of folic acid. It can be added to the diet. The gene has to do with the metabolism of folic acid.
It was thought that there had to be two mutant copies of the gene to raise the NTD risk. Now it is clear that even one copy of the mutant gene can raise the NTD risk. Even one gene can spell trouble.