One of the most important events in the life of the theory that mercury poisoning causes autism was the publishing of a paper by several anti-vaccination activists titled “Autism: A Unique Type of Mercury Poisoning”. This paper has numerous problems, including the fact that its authors are not scientific researchers, it was published in a hugely obscure journal, it was not subjected to peer review, and that many of the symptoms of autism and mercury poisoning that are compared as the basis for the paper are either not symptoms of such conditions or are very rare symptoms that do not typify the conditions. This paper can be harshly critiqued through the simple application of logic.

Sharing Symptoms does not Mean Common Causation

While there is some overlap between the symptoms of autism and mercury poisoning (such as sensory processing abnormalities and mental retardation), they are very distinct entities. Flu and cold are often indistinguishable at the beginning of the illness, with symptoms such as a stuffy nose, aches and pains, and fever common in both. Many disorders from scarlet fever to tuberculosis share characteristics like malaise and lethargy. Most disorders resulting from infectious diseases, as well conditions caused by diverse agents like gunshot wounds and spider venom, share common biological symptoms such as immune system activation. That doesn’t mean those disorders or conditions have shared causation. However, shared causation is the operative assumption for many who tie mercury poisoning to autism, as well as the intended conclusion of the authors who wrote the above referenced paper. This is an example of the correlation does not imply causation logical fallacy.

Autism and Mercury Poisoning do not Share Many Core Symptoms

In order to make their case, the authors of the above paper focused very much on symptoms that are not at the core of the disorders, symptoms that vary from individual to individual and are by no means universal or even common in autism or mercury poisoning. When you compare the main symptoms that define the disorders according to the scientific standards, the differences between the conditions becomes clear.

Autism is primarily classified by a triad of symptoms of communication abnormalities, social withdrawal, and stereotypic behaviors. Other very common symptoms include eye contact avoidance, insistence on patterns and routine, and frequent melt downs. According to Environmental Protection Agency, the following are the main symptoms of mercury poisoning:

• Impairment of the peripheral vision
• Disturbances in sensations ("pins and needles" feelings, numbness) usually in the hands feet and sometimes around the mouth
• Lack of coordination of movements, such as writing
• Impairment of speech, hearing, walking;
• Muscle weakness
• Skin rashes
• Mood swing
• Memory loss
• Mental disturbance

If you compare the core symptoms, the areas of overlap are limited. These differences have not been lost on medical researchers. For instance, Karin Nelson, a neurologist from NIH, showed these two disorders were in fact quite different in a journal article. She described how children with mercury poisoning suffer narrowing of their fields of vision, whereas autistic children don’t have visual problems; children with mercury poisoning can become severely psychotic, whereas children with autism, although socially aloof, aren’t psychotic; and, children with mercury poisoning have heads that are smaller than normal, whereas children with autism tend to have heads that are larger than normal.

Autistic Kids Don’t Have Many Symptoms of Mercury Poisoning

Even if autism were to be a symptom of mercury poisoning, this does not explain why autistic kids don’t display other core symptoms of mercury poisoning that are well understood as symptoms. Autistic children don’t display the memory loss, muscle weakness, impairment of peripheral vision, and other symptoms that characterize mercury poisoning. No one that I am aware of has explained why this should be, why (under the thimerosal theory of autism) children exposed to ethyl mercury only develop certain symptoms that are not recognized as core to mercury poisoning (autism) but do not display symptoms that are absolutely core to mercury poisoning (problems walking).