What causes autism? By this I don't mean what is to blame i.e. Vaccines, Gluten or Pharmaceuticals etc.. I mean what exactly is happening in the brain to cause the autistic behaviors such as little to no communication skills, regression of skills around age 3, hand flapping etc.. I see a lot of research looking for something to blame however I see little to no research on identifying the physical causes or links (maybe I'm not using the correct search terms).

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    $\begingroup$ There's a significant body of anatomical research that is going on, both in neuropathology and neuroimaging, see ncbi.nlm.nih.gov/pubmed/21360830 for example. $\endgroup$
    – jonsca
    Jul 4, 2013 at 20:38

4 Answers 4


Fragile X syndrome is a genetic disorder which is highly related to autism and is considered to be the most common single gene association with autism.

Establishing what actually happens in autistic people is difficult because it is hard to quantify someone as being autistic or not - it is common for some people to show some signs of autistic type behaviour and some people are more extreme than others - plus the symptoms are numerous:

Clinically, autism is defined by a “triad” of deficits comprising impaired social interaction, impaired communication, restricted interests, and repetitive behaviors.

Wikipedia splits the mechanisms in to two key groups, pathophysiology and neuropsychology. The pathophysiological aspects are perhaps better documented and some known correlates to autism are listed:

Our understanding of the mechanisms causing autistic behaviours does not go much beyond this. This paper is a review of the neuroanatomic associations with autism which could, at least in part, help you to identify the physical differences linked to autism.

  • $\begingroup$ Here is a brand new article on autism the-scientist.com/?articles.view/articleNo/36379/title/… $\endgroup$
    – rg255
    Jul 14, 2013 at 9:45
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    $\begingroup$ It's also worth noting that conditions aren't always due to single gene mutations and their aetiology can be more complex. Autism could easily be the result of 10 different gene mutations affecting different processes during brain development (e.g. receptor trafficking, spine growth and all sorts of stuff). The same is true for loads of psychiatric conditions $\endgroup$
    – Jam
    Nov 27, 2018 at 12:04

I would like to asnwer this question. I will try to avoid repeating any information about possible causes of autism, which was mention here. Anyway there is new interesting information.

Autism spectrum disease (ASD) is typically diagnose from the psychological point of view. Such thing like repetitive behavior, echolilia, stimming and stuff like that. True reason why does we still diagnose ASD in this way is because we still dont know causes of this disorder.

Sleep inconsistency

Kids with ASD are well know for theirs sleep disturbance.

Polysomnography studies of ASD children showed most of their abnormalities related to rapid eye movement (REM) sleep which included decreased quantity, increased undifferentiated sleep, immature organization of eye movements into discrete bursts, decreased time in bed, total sleep time, REM sleep latency, and increased proportion of stage 1 sleep.

REM sleep is one of the two types of sleep in general. By the ontological point of view the REM sleep might provide neural stimulation. In this way good sumury provide us at wikipedia page on REM:

REM sleep prevails most after birth, and diminishes with age. According to the "ontogenetic hypothesis", REM (also known in neonates as active sleep) aids the developing brain by providing the neural stimulation that newborns need to form mature neural connections.Sleep deprivation have shown that deprivation early in life can result in behavioral problems, permanent sleep disruption, and decreased brain mass,and can result in an abnormal amount of neuronal cell death.unreliable medical source? The strongest evidence for the ontogenetic hypothesis comes from experiments on REM deprivation and the development of the visual system in the lateral geniculate nucleus and primary visual cortex.

So lack of REM sleep can be one of the many important factor to autism brain development.

Autistic microbiom

Microbiome is an ecological community of commensal, symbiotic and pathogenic microorganisms found in and on all multicellular organisms studied to date from plants to animals.

Recent studies suggest that autism is often associated with dysregulated immune responses and altered microbiota composition. This has led to growing speculation about potential roles for hyperactive immune responses and the microbiome in autism. Yet how microbiome–immune cross-talk contributes to neurodevelopmental disorders currently remains poorly understood. In this study, we report critical roles for prenatal microbiota composition in the development of behavioral abnormalities in a murine maternal immune activation (MIA) model of autism that is driven by the viral mimetic polyinosinic-polycytidylic acid. We show that preconception microbiota transplantation can transfer susceptibility to MIA-associated neurodevelopmental disease and that this is associated with modulation of the maternal immune response. Furthermore, we find that ablation of IL-17a signaling provides protection against the development of neurodevelopmental abnormalities in MIA offspring. Our findings suggest that microbiota landscape can influence MIA-induced neurodevelopmental disease pathogenesis and that this occurs as a result of microflora-associated calibration of gestational IL-17a responses.

It may not sound like something related to the neural system but now study lift up mircobiome importance.

EECs play an important role in gut chemosensing to orchestrate appropriate functional responses to a variety of stimuli ranging from nutrients, food degradation products, toxic chemicals, microorganisms and bacteria products. This complex balance between maximizing nutrient assimilation and minimizing danger to maintain optimal homeostasis is the result of the interplay of different detection systems including the distinct types of sensory receptors expressed by EECs, the variety of signaling molecules released by EECs and the targets that are activated directly and indirectly such as neighboring cells, distant targets reached via the bloodstream and neuronal pathways. Considerable progress has been made in understanding EECs relationship with neurons of the ENS and CNS and EEC bidirectional communication with the brain. There is now strong evidence that EECs can directly participate in the brain-gut axis bidirectional communication through axon-like processes or basal cytoplasmic processes. The basal processes connect EECs and neurons innervating the gut forming neuroepithelial circuits, which allow sensory transmission from the gut lumen and feedback from the brain to the gut EECs. The activation of afferent and efferent nerve pathways may be explored for the management of diseases related to feeding disorders and GI dysfunction. Alterations in the bidirectional communication between the brain and the gut are likely associated with an impairment of gut functions (e.g. intestinal secretion, motility, blood flow and afferent sensitivity). The modification of the homeostatic reflex might lead to a chronic perturbation of the gut such as visceral hypersensitivity. Therefore, a better understanding of the EEC roles and their relationship with the brain and sensory nerves is an important research target. Future studies are required to fully decipher this complex network. The direct EEC to nerve connection opens a new horizon of research and provides new tools to understand the mechanisms underlying EEC control of food intake and GI dysfunction as well as potential new therapeutic targets.

I think there more and more clues that the biggest role in development may be complexes imune reactions on brain development such as recent relation was found in homosexual brain development


Devnani, P. A., & Hegde, A. U. (2015). Autism and sleep disorders. Journal of pediatric neurosciences, 10(4), 304-7.

Why We Sleep: Unlocking the Power of Sleep and Dreams book by Matthew Walker

Cutting Edge: Critical Roles for Microbiota-Mediated Regulation of the Immune System in a Prenatal Immune Activation Model of Autism

Latorre, R., Sternini, C., De Giorgio, R., & Greenwood-Van Meerveld, B. (2015). Enteroendocrine cells: a review of their role in brain-gut communication. Neurogastroenterology and motility : the official journal of the European Gastrointestinal Motility Society, 28(5), 620-30.


While still not entirely clear as to what causes autism, there is a growing body of research (as jonsca said), and a model is being developed.

A suggested explanation from "Causes of Autism Spectrum Disorders", that the disorder may begin in utero, with the interaction of genes and nutrients. However,

recent research suggests that Autism may result when a child with a genetic susceptibility and/ or abnormal Omega-3 fatty acid profile in cell membranes is exposed to one or more environmental insults (heavy metal exposure, virus or bacteria) resulting in malfunctioning cells (often in the gut and brain). This can happen “in utero” (during pregnancy) or after birth (post-partum). (from the first link).

Genes seem to certainly play a role, as in the article "Support for the homeobox transcription factor gene ENGRAILED 2 as an autism spectrum disorder susceptibility locus." (Benayed et al. 2005), the homeodomain transcription gene EN2 are associated with Autism, associated with about 40% of the people they tested.

Disorders in the serotonergic system have also been found to be a mechanism of autism, according to "Serotonin transporter genotype and neuroanatomy in autism spectrum disorders" (Raznahan et al. 2009).

I hope this goes part of the way in answering your question.


Cerebral folate deficiency (CFD) has been found to be the cause of autism in as many as 75% of autism patients. Specifically, the folate uptake into the brain occurs primarily through folate receptors in the choroid plexus. Folate receptor alpha antibodies (FRAA) in autism patients, bind to these folate receptors and block folate uptake. Folate is of course an essential nutrient for various brain functions. So one can expect numerous brain functions to be impacted by CFD.

Cerebral folate receptor autoantibodies in autism spectrum disorder https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3578948/

Folinic acid (not to be confused with folic acid) has been used to treat CFD induced autism. Basically, it is a method of getting folate to the brain by an alternate pathway, that bypasses the primary path that is blocked by FRAA.

Folinic acid improves verbal communication in children with autism and language impairment: a randomized double-blind placebo-controlled trial https://www.nature.com/articles/mp2016168

  • $\begingroup$ I know it's been about a year since you posted this but, I'm just now seeing this one... thank you! $\endgroup$ Apr 8, 2019 at 16:06

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