In the 1950s many psychoanalysts who followed the Freudian belief system argued that the condition of autism resulted from parental withdrawal from the infant. The mother is blamed primarily for the child's condition. The name they chose for these dysfunctional mothers was “refrigerator mothers,” due to their cold-hearted nature. These women were told that they needed to pay more attention to their children or that they were disciplining them too harshly. However, there are some theories that have been examined in recent years. Such as family genetics which is passed down from a parent to the child and there could also be environmental reasons. No one knows exactly how the environment caused ADS; some theorize that vaccines are responsible for the sudden onset of ADS. In fact, the measles vaccine is said to cause autism by damaging the stomach lining. Thimerosal is a preservative found in vaccines, contains mercury and has been linked to this disease. It has also been theorized that receiving too many vaccines at one time damages the immune system thus causing autism. Familial genetics research studies have been conducted to identify how many genes are associated with ADS. These studies have revealed irregularities in certain parts of the brain in people suspected of having ADS. There has also been a link to low levels of serotonin or other neurotransmitters in the brain needed to maintain them