Many advocates of a vaccine / autism link often attempt to characterize the world as a very simple place, a place where autism is caused solely or largely by vaccines. Probably the most famous paper on autism was written in 2001 by a series of individuals intensely dedicated to the belief vaccines cause autism, including Sallie Bernard and Lyn Redwood. The name of the paper: Autism, a Unique Form of Mercury Poisoning - very simple, and very persuasive to the average person looking for a simple explanation for autism, which is what most people would prefer. This paper changed the minds of probably millions of people worldwide in part because of its simplicity, despite the fact that it was massively flawed in many ways (from the lack of qualification of its authors, to the journal in which it was published, to the lack of peer review, to the speciousness of its claims).

Unfortunately, the world is not that simple – if it were, eliminating autism would be pretty easy. On the contrary, lots of wildly unrelated and divergent factors can cause autism / contribute to its causation / make autism more likely to develop in certain individuals, none of which involve mercury poisoning as far as I am aware. These include:

• Chromosomal abnormalities including fragile X syndrome, Down syndrome, Rett syndrome, Angelman syndrome, Prader-Willi syndrome, Smith-Lemli-Opitz syndrome, tuberous sclerosis, Cornelia de Lange syndrome, epilepsy, cerebral palsy, neurofibromatosis, Duchenne muscular dystrophy, Aarskog syndrome, Hypomelanosis of Ito, Joubert syndrome, Moebius syndrome and Williams syndrome;

• Metabolic disorders including phenylketonuria and various mitochondrial disorders that likely result in lactic acidosis;

• Exposure to various environmental toxins / substances prenatally including alcohol, thalidomide, valproic acid, and misoprostol;

• Maternal exposure during pregnancy to various infectious agents including rubella, encephalitis, and influenza;

• Fetal exposure to various maternal life stressors, particularly during weeks 24 to 30 of gestation;

• Various parental characteristics such advanced paternal age.

As evidenced above, both genetics and environment contribute to autism. Also, autism causation can be simple, or it can be complex. Single vector genetic abnormalities (changes in a single gene) can cause a dramatic increase in the likelihood of autism developing autism (fragile x syndrome). So can a single vector environmental exposure (prenatal valproic acid). However, many if not most cases of autism (idiopathic cases) involve complicated causation, including genetic susceptibility likely involving dozens if not hundreds of genes, and the potential for multiple environmental factors working together to trigger or cause autism in genetically susceptible populations..

Moreover, autism is not a single disease entity. There are five specific diagnoses that fall on the autism spectrum from low functioning variants like childhood autism and childhood disintegrative disorder to high functioning variants like pervasive developmental disorder and Asperger’s Syndrome. There is tremendous variation in symptoms and function level within these spectrum disorders. In fact, within autism there are not only abnormal behaviors and deficits but there are often extraordinary areas of competency such as memory and puzzle solving – a set of characteristics not indicative of simple causation through a detrimental genetic mutation or toxic exposure. And, there are many individuals who share characteristics with those who are autistic, but who are not sufficiently disordered to receive a diagnosis; they are often considered to be on the broad autism phenotype of personalities.

Autism is truly complex. This vast complexity does not seem to imply a world in which simple autism causation could be a reality – autism being caused by vaccinations. The logic does not work. It certainly is not as simple as autism being a unique form of mercury poisoning. Autism is a convergent disorder, meaning many unrelated factors can result in autistic behaviors emerging. We know of a couple dozen factors that are clearly involved in autism. Ignoring these and all the other potential factors, from daily exposure to toxic chemicals to maternal stress to increasing obesity – factors we know readily cause human harm - to focus such attention and blame on vaccinations (which have been one of the miracles of modern medicine and have not been shown to cause substantial human harm) just doesn’t make a lot of sense.