If a baby is born with birth defects affecting the brain there may be serious long-term implications. Brain birth defects may lead to problems affecting the functioning of the brain or may lead to abnormal development of the brain as the child grows older. This may affect the child's mobility, their intellectual and mental development, communication ability and the development of different senses such as sight and hearing, and some may even be fatal. Most brain birth defects arise from genetic mutations, which can be inherited or may be caused by environmental factors, for example if the mother smoked, drank alcohol or took drugs while pregnant. Genetic defects may also cause a physical malformation of the head. Some of the more common examples of genetic brain birth defects include Tay-Sachs disease and Wilson disease.