What Causes Autism, Autism Connect

Parents of children with autism usually have a few unanswered questions such as "How did my child develop autism?" "My child was absolutely fine and had even started to pick up a few words. What happened all of sudden?" "Is autism acquired?" "Could it have been prevented?" "Is it genetic?" "Can my other children also have autism?"

Medical science does not have answers for many of these questions, and although the "why" may never be known, what is becoming clearer with ongoing research is, "What is the fundamental problem in the brains of the children with Autism".

In autism, though the brain structure looks normal, there are functional abnormalities in specific regions of brain. This information, about the functioning of brain areas can be obtained from functional neuroimaging techniques like PET-CT scan and functional MRI scan of the brain. These imaging studies permit the study of the abnormal pattern of cortical activation in autism. These studies indicate that certain areas of the brain show reduced functioning like mesial temporal lobe (innermost part of the brain responsible for learning, understanding, memory, social interaction and abstract thinking), frontal lobe (the front part of the brain responsible for emotions and aggression) and cerebellum (responsible for balance, coordination, muscle tone and speech). Hence the dysfunction of these areas are responsible for problems seen in autism.

Positron Emission Tomography – Computed Tomography Scans showing areas of brain with reduced function

Research has also helped us to know that there isn’t one cause of autism but multiple risk factors that increase the risk of a child developing autism. Most cases of autism seem to be caused by a combination of autism risk genes and environmental factors influencing the early brain development. Over the last five years, scientists have identified a number of rare gene changes or mutations which have been associated with autism. Other factors related to children with autism and their parents that may contribute to increase the risk of Autism have also been identified. Along with these certain environmental factors have also been included in the risk factors for Autism.

Computed Tomography Scans, What Causes Autism, Autism Connect

Below mentioned are a few probable causes of autism:

Patient and Family Related Factors in Autism, What Causes Autism, Autism Connect.

Patient and family related factors:

Gastrointestinal Diseases

It has been observed that gut microbiota affects the brain development and function. This was especially observed during various mice studies which indicated abnormal psychiatric symptoms in mice with abnormal gut microbiota. This theory has been extrapolated in Autism as well. The two gut related factors that are postulated as causes in Autism are firstly, the abnormal micro bacterial population in the gut of the children and second, the impaired carbohydrate metabolism by the intestinal cell lining. Many abnormalities in the intestinal cell lining such as ileo-colonic lymphoid nodular hyperplasia, enterocolitis, gastritis, and esophagitis, have been observed in various studies. A disruption of enterocyte membrane with increase inflammation in the gut has also been seen. Inflammatory markers such as cytokines, immunoglobulins and lymphocyte profiles are known to be altered in children with Autism, which leads to an increased permeability of intestines, and deficient activity of enzymes. Studies have also shown a strong correlation between the severity of autism and gastrointestinal problems. Commonly, the GI disorders observed in children with Autism, are chronic constipation, diarrhoea, gastroesophageal reflux disorder (GERD) and a gluten or casein intolerance..

Genetics Factors

Genetic factors are thought to be some of the most significant causes for autism spectrum disorders. It was earlier estimated that genetics could explain the occurrence of autism in over 90% of patients, however, thorough studies later proved that this was an overestimate.  

In a twin study conducted, it was found that many non-autistic co-twins had learning or social disabilities, thus, making it difficult to explain the occurrence of autism, purely on the basis of genetics. Therefore, whether or not a child would autistic, depends on how different genes interact with one another, what their penetrance or response to a certain feature or characteristic is,  the defect in the gene, environmental triggers and many other factors

A common hypothesis is that autism is caused by the interaction of a genetic predisposition and an early environmental insult. There are several theories based on environmental factors that have been proposed to address the remaining risk. Some of these theories focus on prenatal environmental factors, such as agents that cause birth defects, and others focus on the environment after birth, such as children’s diets.

Environmental factors:

Environmental factors play a role in increasing risk of Autism. With urbanization and industrialization we are exposed to chemical pollutants in air, water, soil and therefore even the food we eat. With advent of technology we are exposed to more and more electromagnetic radiations. These elements are presumed to contribute to increased risk of Autism.

Role Of Electromagnetic Radiations, What Causes Autism, Autism Connect

We've all heard that electromagnetic radiations from the electronic devices we use affect brain function. To get down to the technicality of this statement, electromagnetic radiations can alter  the biological electric activity of the brain, thus, increasing blood brain barrier permeability and inducing epigenetic modifications. This can therefore, potentially alter damage brain cells and thus affect brain development. Wireless radiations, especially, emitted from the gadgets we regularly use, such as cellphones, etc. can potentially contribute to neuroinflammation. Prolonged or regular exposure to wireless radiations during pregnancy may affect not just the mother, but also the fetus. Children exposed to constant wireless radiations early in the childhood may also experience harmful effects of the radiation. These radiations are presumed to interfere with the ability of human body to excrete heavy metals. This can lead to heavy metal accumulation inside cells thus, causing toxicity. Reducing the exposure to wireless radiation has shown reduction in the symptoms of Autism in some instances. Although, the evidence for the causative effect of these radiations is very minimal at the moment, it warrants further investigation.

References:

 

1. Gastrointestinal flora and gastrointestinal status in children with autism-comparisons to typical children and correlation with autism severity. Adams JB, Johansen LJ, Powell LD, Quig D, Rubin RA BMC Gastroenterol. 2011 Mar 16; 11:22.

2. Normal gut microbiota modulates brain development and behavior. Heijtz, R. D., Wang, S., Anuar, F., Qian, Y., Björkholm, B., Samuelsson, A., … Pettersson, S. (2011). Proceedings of the National Academy of Sciences of the United States of America, 108(7), 3047–3052.

3. Impaired Carbohydrate Digestion and Transport and Mucosal Dysbiosis in the Intestines of Children with Autism and Gastrointestinal Disturbances. Williams, B. L., Hornig, M., Buie, T., Bauman, M. L., Cho Paik, M., Wick, I., … Lipkin, W. I. (2011). PLoS ONE, 6(9), e24585.

4. Biological plausibility of the gut-brain axis in autism. Vasquez A. Ann N Y Acad Sci. 2017 Nov;1408(1):5-6

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6. Chugani DC, Muzik O, Behen M, Rothermel R, Janisse JJ, Lee J, Chugani HT. Developmental changes in brain serotonin synthesis capacity in autistic and nonautistic children. Annals of neurology. 1999 Mar 1;45(3):287-95.

7. Schifter T, Hoffman JM, Hatten JR HP, Hanson MW, Coleman RE, DeLong GR. Neuroimaging in infantile autism. Journal of Child Neurology. 1994 Apr;9(2):155-61.

8. Mountz JM, Tolbert LC, Lill DW, Katholi CR, Liu HG. Functional deficits in autistic disorder: characterization by technetium-99m-HMPAO and SPECT. Journal of Nuclear Medicine. 1995 Jul 1;36(7):1156-62.

9. Zürcher NR, Bhanot A, McDougle CJ, Hooker JM. A systematic review of molecular imaging (PET and SPECT) in autism spectrum disorder: current state and future research opportunities. NeurosciBiobehav Rev. 2015 May;52:56-73.

10. Wang C, Geng H, Liu W, Zhang G. Prenatal, perinatal, and postnatal factors associated with autism: A meta-analysis. Medicine (Baltimore). 2017 May;96(18):e6696

11. Modabbernia A, Velthorst E, Reichenberg A. Environmental risk factors for autism: an evidence-based review of systematic reviews and meta-analyses. Mol Autism. 2017 Mar 17;8:13

12. Wakefield AJ, Murch SH, Anthony A, Linnell J, Casson DM, Malik M, Berelowitz M, Dhillon AP, Thomson MA, Harvey P, Valentine A. RETRACTED: Ileal-lymphoid-nodular hyperplasia, non-specific colitis, and pervasive developmental disorder in children.

13. Plotkin S, Gerber JS, Offit PA. Vaccines and autism: a tale of shifting hypotheses. Clinical Infectious Diseases. 2009 Feb 15;48(4):456-61.



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