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Causes of autism

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The causes and etiology of autism are an area of debate and controversy. Current thought among most stipulates that the causes of Asperger syndrome are the same as those of autism.[[Citing sources citation needed]] Some disagree, arguing that Asperger syndrome and autism have different causes.[[Citing sources citation needed]] All of this happens while the broader debate over whether Asperger's and other conditions (such as ADHD) are part of the so-called autism spectrum continues. [[Citing sources citation needed]]

Some theories argue more strongly for Asperger syndrome than autism. It is sometimes argued that some particular theories play a bigger role in Asperger syndrome, such as the social construct theory. However, this is a controversial area.

Contents

Physical disorder models

In his 2003 book The Essential Difference, professor Simon Baron-Cohen of the Autism Research Centre argued for the extreme male brain theory, which suggests that Asperger syndrome and autism represent an extreme form of the way in which men's brains differ from those of women[#endnote_BaroncohenSexdifferences][#endnote_BaroncohenExtreme]. As a result, people with Asperger Syndrome are good (often very good) at systemizing and very bad at empathizing [#endnote_guardianest][#endnote_LawsonSystemising]. The theory is linked with Baron-Cohen's "empathizing/systemizing (E-S)" theory which states that, in general, men are better at systemizing than women, and that women are better at empathizing than men due to physical differences between male and female brains.[[Citing sources citation needed]] Hans Asperger himself said that his patients had "an extreme version of the male form of intelligence."[[Citing sources citation needed]]

The concept of differing types of intelligence in males and females is controvesial though, and remains speculative.[[Citing sources citation needed]]

The preoperational-autism theory states that autistic people are those who become neurologically impeded at the preoperational stage of cognitive development, where much of information processing is at a holistic-visual level and largely musical and nonverbal. This also addresses the issue of the theory of mind where children (autistic and non-autistic) at the preoperational stage of cognitive development have not attained decentralization from egocentrism.[[Citing sources citation needed]]

Underconnectivity theory theorizes that autism is a system-wide brain disorder that limits the coordination and integration among brain areas. With the aid of fMRI, it was seen that white matter, which connects various areas of the brain like cables, has abnormalities in people with autism. This theory may be related to the "lack of central coherence" theory proposed by Uta Frith, which suggests that children with autism are good at paying attention to detail but have difficulty integrating information from a range of sources.[[Citing sources citation needed]]

This theory says that the autistic person has "mind blindness", or the inability to create models of other people's thoughts. The typical example of this is the Sally-Anne test where the subjects have to try to determine what a third party's action will be (see theory of mind also). Some people with autism do not seem to fit this model, however.[[Citing sources citation needed]]

In some instances, brain areas that are active during the observation of hand-movements are silent in autistic individuals [#endnote_refbot.766]. The activity is markedly enhanced in non-autistic persons.[[Citing sources citation needed]] So the social deficits observed in autism could be the result of a faulty mirror neuron system, which could also prevent normal development of empathy.[[Citing sources citation needed]]

There's increasing suspicion among researchers that autism is not a condition with a single cause, but a number of yet unidentified conditions with different causes.[[Citing sources citation needed]]

Etiology theories for physical disorder models

While the etiology of autism is largely unknown,[[Citing sources citation needed]] there is no shortage of theories in the area. In part, the mystery of autism has been slow to resolve due to its relatively recent identification as a disorder, and because government funding of autism research lags far behind that of less common diagnoses,[[Citing sources citation needed]] such as juvenile diabetes. What funding is available has largely been directed toward epidemiological research, rather than clinical studies investigating possible environmental triggers. In addition, in recent times the recorded incidence of autism has risen dramatically.[[Citing sources citation needed]]

For more details on this topic, see Heritability of autism.
Autism is known to be highly heritable.[[Citing sources citation needed]] Research done by some institutions seek to find a way for early and more accurate detection of autism similar to Rett syndrome. Instead of searching for one particular gene as the cause for autism, many of the studies tend to search for complex interactions between a number of genes.[[Citing sources citation needed]]

A 2005 study done by the Duke Center for Human Genetics at Duke University finds some evidence that complex interactions between GABA (gamma aminobutyric acid) receptor genes might be part of the cause of autism. One of the functions of the GABA genes is to inhibit the nerve system from firing. The theory is that somehow GABA genes suffer damage of some kind, leading to an overwhelmed sensory system causing the characteristics or symptoms of autism.[#endnote_dukegeneticspressrelease],[#endnote_dukegenetics]

Simon Baron-Cohen proposes a model for autism based in his empathising-systemising (E-S) theory[#endnote_guardianest2]. His team at the Autism Research Centre in Cambridge, UK, measured testosterone levels in the amniotic fluid of mothers while pregnant. This is presumed to reflect levels in the babies themselves. The team found that the babies with higher fetal testosterone levels had a smaller vocabulary and made eye contact less often when they were a year old.

His group has looked at the original 58 children again, at age four. The researchers found that the children with higher testosterone in the womb are less developed socially, and the interests of boys are more restricted than girls. The results are published in the Journal of Child Psychology and Psychiatry in a 2004 issue [#endnote_BaronCohen2004CPP].

Baron-Cohen theorizes that high fetal testosterone levels push brain development towards an improved ability to see patterns and analyze systems. Males supposedly tend to be better at these tasks than females. But the high levels are thought to inhibit the development of communication and empathy, which are allegedly typical female skills. (New Scientist, May 24 2003) [#endnote_BaronCohen2003NS].

However, there is still no demonstrable evidence that testosterone levels affect brain development or autism. Gender or biodeterminism is a fashionable explanation for many human behaviors, but has been challenged by other professionals[#endnote_bttchallenge].

Children exhibiting behavioral and learning disorders may do so in part because of diets deficient in vital nutrients needed for their brains to function normally.

In 1998, a small study published in the Lancet found a consistent set of bowel disorders among a dozen autistic children. Although an emphasis was placed by the authors on a possible link to the MMR vaccine, the study also suggested nutritional deficits caused by bowel disorders may have contributed to the onset of neurological disorders.

Some children with autism have responded well to dietary intervention such as eliminating gluten (a protein found in most grains) and casein (the protein found in milk) as well as phenyls and food coloring (see Feingold diet). Most data regarding the validity of these interventions have been the subjective observations of parents and caretakers and no scientific study with proper subject elimination has taken place. Possible determining factors regarding the effectiveness of this as a treatment involve coincidence of a combination of asthma, eczema, diarrhea and constipation, strange "yeasty" diaper rash, and uncharacteristic eating habits (eating an entire loaf of bread).

Several unproven theories behind the effectiveness of this as a treatment involve damage to the lining of the stomach and/or intestines allowing the proteins to be improperly metabolized as glutomorphine and casomorphine which are both opiates. The damage to the gut lining is theorized to be caused by immunio-abnormalities and possibly the incidence of early oral-antibiotic use combined with a genetic predisposition.

Increased intake of folic acid by pregnant women roughly coincides with the reported increase in the prevalence of autism. The explanation offered is that folic acid allows more brain cells to survive than should. This hypothesis is untested at this point. [link]

Controversial research by Andrew Wakefield in the UK that was published in The Lancet in the February 1998 issue, dubbed the "Wakefield Study", suggested a possible link between autism and the MMR vaccine. The original research has come under criticism, largely due to an alleged conflict of interest on Wakefield's part [#endnote_Wakefieldconflict]. In March 2004, almost all of the paper's authors retracted its "interpretation" section, which claimed a potential link between pervasive developmental disorders and "possible environmental triggers".

Critics have claimed that Wakefield's study contains many obvious flaws, including an inability to recognize bias in his sample. In October 2005, a study by the respected Cochrane Library said, on the basis of 31 pieces of research into the possible side effects of MMR, that it found no association between MMR and autism. Several independent groups, including the National Academy of Sciences, have also conducted investigations and concluded that the evidence does not support a link.

One study by Gillberg and Heijbel in 1998 examining the prevalence of autism in children born in Sweden from 1975 to 1984[#endnote_gillbergheijbel] found no difference in the prevalence of autistic children born before the introduction of the MMR vaccine in Sweden and those born after the vaccine was introduced. Another study, conducted by Madsen and other researchers in 2002, studied all children born in Denmark from January 1991 through December 1998[#endnote_madsenetal]. There were a total of 537,303 children in the study; 440,655 of the children were vaccinated with MMR and 96,648 were not. The researchers did not find a higher risk of autism in the vaccinated than in the unvaccinated group of children.

Research in the U.S. has suggested a similar link between autism and the DPT vaccine, although this is not referenced. However, contrary to early claims from Wakefield, it is doubtful that a large majority of autism cases would come from this vaccine. Despite all the evidence to the contrary, controversy surrounding autism and vaccines continues to this day, and many polls, such as the autism coach poll[#endnote_autismcoachpoll], which involved only 15 respondents, show vaccines as the most popular theory currently on the etiology of autism among parents of autistic children.

In a controversial article in June 2005, Robert F. Kennedy, Jr. described research suggesting that it is not the vaccines themselves, but a mercury-based preservative called thiomersal, used in some vaccine preparations (although not MMR), that may be a cause of autism[#endnote_kennedythimerosal]. Kennedy argues that autism was first observed in children who were born around the time of introduction of thiomersal into mass-produced vaccines, and that the incidence of autism in the United States is well correlated with the amounts of thiomersal children receive during their first two years of life. Kennedy also noted that the there is a low reported incidence of autism in the Amish, who do not immunize their children. Kennedy states that is an exception, the rare child who was immunized.[[Citing sources citation needed]] However, the CDC has described a link between thiomersal and autism as 'unlikely'.[#endnote_www.cdc.gov.767]

In 1999 the Public Health Service (including the CDC, FDA, and NIH) recommended that thiomersal no longer be used in vaccine preparations. While it was by 2005 utilized in only a very few childhood vaccines, it has not been established that autism rates have dropped significantly. The CDC and some medical organizations continue to assert that no available evidence supports a causal link between thiomersal and autism. Critics have in turn claimed that the CDC analysis demonstrates deliberate bias in the CDC research[#endnote_www.generationrescue.org.75].

For example, an analysis by Madsen et al. in Demark noted that the incidence of autism remained fairly constant while thiomersal was being phased out and started to rise beginning in 1991, even after thimerosal was discontinued in 1992.[#endnote_MasdenThimerosal] Critics of this analysis point out that the methodology was biased[#endnote_www.generationrescue.org.76], [#endnote_www.generationrescue.org.77]. Dissenters to the Denmark data point out a significant increase in autism rates[#endnote_www.generationrescue.org.78] among children whose childhood vaccines contained thiomersal. However, in Madsen et al.'s study, the amount in the vaccinations actually decreased while autism rates increased (specifically, during the period 1961–1970, infants had received a total of 400 µg of thiomersal by the age of 15 months, and during the period 1970–1992, infants had received a total of 250 µg at 10 months of age).

The California Department of Developmental Services (DDS), considered to have the best reporting system for autism in the US[#endnote_www.littlecanaries.org.768], has reported unprecedented decreases in the caseload increase. The caseload increase went from 734 during the second quarter of 2005 to 678 during the third quarter of 2005, a 7.5% decline in one quarter. Note that the total caseload handled by the state is still increasing, but the recent trend points to a deceleration in the trend. For example, from the 2nd to the 3rd quarter of 2004, the caseload went from 25,020 to 25,769 (a increase of 749 clients). Between the 1st and 2nd quarter of 2004, the caseload increased from 24,297 to 25,020 (a increase of 723 clients). These variations have led to speculation that removal of thiomersal from vaccines in California is starting to pay off. Others point out they are unremarkable and may simply be an indication that the awareness curve is starting to level off, and that the rate of caseload increase should be expected to decrease to population growth levels (1.6% annual) eventually. Caseload increase between 2004 and 2005 was about 10%.

A study published in the March 2006 issue of the Journal of American Physicians and Surgeons (JPANDS) by Dr. Mark Geier claimed to show that "new cases" of autism in California dropped as much as 35% following removal of thimerosal from vaccines. However, the study did not document incidence drops, and its definition of "new cases" is known to be flawed.

A study published in May 2006 by Dr. Mark Geier et al. indicates that the trends of newly diagnosed neurodevelopmental disorders (NDs) such as autism reported to VAERS "correspond directly to the expansion and subsequent contraction of the cumulative mercury dose to which children were exposed from TCVs through the U.S. immunization schedule."Geier DA, Geier MR. Early Downward Trends in Neurodevelopmental Disorders Following Removal of Thimerosal-Containing Vaccines. Med Sci Monit. 2006 May 29;12(6):CR231-239. PMID 16733480 [full text (pdf)]

A study due to be published in July 2006 claims that the MMR vaccinations are definitely not the cause of autism and Asperger Syndrome. [article]

Susan Bryson has claimed that some autistics have evidence of trauma to the brain stem in early development, and that a small portion of the thalidomide victims have become autistic. The victims' limbs were normal unless thalidomide use continued later in the pregnancy. The brain stem anomaly's most striking feature is inability to focus attention away from a stimulus in a short time like neurotypicals, as demonstrated in a psychological test.

Some people claim the inability to shift attention quickly interferes with the ability to read nonverbal language where fast attention shifts are needed (such as eye language), suggesting that being nonverbal is not a primary feature of autism. Strong and shiftless focus is, however, a benefit in some areas like science, programming, and advanced mathematics. This is supported by the monotropism hypothesis.

Dr. Bernard Rimland's influential research and his book Infantile Autism (1967) argued that autism was not caused by childhood trauma or abuse, but by damage to certain areas of the brain, particularly the reticular formation which associates present sensory input with memories of past experiences. Dr. Rimland is a foremost advocate of the theory that autism may be precipitated by mercury and heavy metal toxicity[#endnote_curezonemercury]. He also is prominent in increasingly common claims of successful treatment of autism in children—particularly regarding improvements in ability to comprehend the spoken word—with the gluten-free, casein-free diet and mercury chelation therapy.

Others claim Dr. Bernard Rimland's methods alleviate the symptoms of heavy metal poisoning, but not autism. Curing heavy metal poisoning when it is present is a worthy goal (it helps with IQ and other learning difficulties as well as general health), but claiming a benefit for autism is a misrepresentation. Heavy metal poisoning may be more common among autistics due to a severe metallothionein deficiency, but more evidence is needed to substantiate the idea that heavy metals cause autism. It is still being studied. The presence of heavy metals, particularly mercury, might make an autism diagnosis more likely, however.

A growing body of peer-reviewed studies published in mainstream journals has shown that many common diseases of previously unknown origin are caused by the presence of slowly acting viruses. For example, cervical cancer is caused by the human papilloma virus; some cases of liver cancer are caused by hepatitis C or B; Schizophrenia may be caused by Borna virus, although some recent evidence[#endnote_anti.borna.schizophrenia] weighs against this. Paul W. Ewald, among others, argues that the available data on the origin of autism is consistent with it being caused by a virus or infection. Alternatively, it was hypothesized that certain antibiotics rather than an infection may be associated with autism; that is, depending on certain conditions they could be either harmful or helpful[#endnote_www.ncbi.nlm.nih.gov.769].

An increasing number of studies in national journals are linking the regulation of the immune system with nervous system diseases such as multiple sclerosis and even Alzheimer's disease. Cognitive function, memory, and fatigue may all be controlled by small molecule immune modulators. Current treatments need to be modified if we confirm that this finding applies to children with autism," says Dr. Jeffrey Galpin, a professor at USC and an infectious disease specialist D'Adamo and Whitney (104-105) report that maternal rubella infection is thought to play a role in some cases of AS. No relationship between AS and reactions to vaccines and other external factors has been clearly proven [#endnote_D'Adamo].

D'Adamo and Whitney (104-105) report that although there is not a published study , an informal accounting shows a marked prevalence of blood type A among AS children. The other blood types have low incidence, risk or severity of AS and Autism. Since the type A limits several dietary lectins that are thought to interfere with secretin, it is not too far-fetched to consider that improvement in these children may have actually resulted from enhancement of their own secretin metabolism [#endnote_D'Adamo]. 

A study by Horvath et. al (1998) on secretin and Asperger's reported that children with Asperger's or Autism and gastrointestinal problems had improved gastrointestinal function after secretin infusion and that the children become more sociable and communicative. They also benefited with a low lectin and wheat diet. This suggest that there might be a gastrointestinal and diet cause of Asperger's or Autism [#endnote_Horvath].



Psychological disorder models




For more details on this topic, see Refrigerator mother.


Dr. Bruno Bettelheim believed that autism was linked to early childhood trauma, and his work was highly influential for decades both in the medical and popular spheres. Parents, especially mothers, of autistics were blamed for having caused their child's condition through the withholding of affection. Leo Kanner, who first described autism (Autistic disturbances of affective contact, 1943) originated the "refrigerator mother" hypothesis, which held that autism was at least partly caused by a lack of affection from the mother. Although Kanner eventually renounced the theory and apologized publicly, Bettelheim put an almost exclusive emphasis on it in both his medical and his popular books. Treatments based on these theories failed to help autistic children, and after Bettelheim's death it came out that his reported rates of cure (around 85%) were found to be fraudulent.




Psychogenic theories in general have become increasingly unpopular, particularly since twin studies have shown that autism is highly heritable. Nevertheless, some case reports have found that deep institutional privation can result in "quasi-autistic" symptoms without the neuroanatomical differences [#endnote_www.ncbi.nlm.nih.gov.79][#endnote_www.ncbi.nlm.nih.gov.80]. Other case reports have suggested that children predisposed genetically to autism can develop "autistic devices" in response to traumatic events such as the birth of a sibling [#endnote_www.ncbi.nlm.nih.gov.81].



Natural variation models


Many people diagnosed with autism and Asperger's syndrome don't think a disease model is appropriate to explain autistic behavior. They argue in favor of the neurodiversity model. Currently, no theories based on the neurodiversity model have been proposed by scientists, but there's no shortage of theories and insight from autistics themselves. Unlike the 'social construct' theory (below), the neurodiversity view is consistent with the eventual existence of an objective test to diagnose autism.




In this model of mind, mental events compete for and consume attention. In a polytropic mind, many interests have a moderate amount of  attention put into them, while in a monotropic mind, the person's attention is put into a few more specialized interests. The theory argues that when many interests are aroused, multiple complex behaviors emerge, but if only a few interests are aroused, fewer—but more intense—behaviors emerge.  A May 2005 article in The Autism Journal [#endnote_autismmonothropism] and information available from the group Autism and Computing[#endnote_AandC] delves further into this subject.



A spectrum disorder such as autism may be understood as a cultural or social construct
. What this theory says is that the boundary between normal and abnormal is subjective and arbitrary, so autism does not exist as an objective entity, but only as a 'construct'. Note that this theory does not say that there are no neurological or quality-of-life differences - in average - between groups deemed 'autistic' and 'non-autistic'. To falsify this theory it would need to be shown that an objective characteristic can clearly separate both groups. For example, a genetic test that can fully substitute for a psychiatric diagnosis would undermine this theory. The kind of phenomena this theory explains well are: (1) Differences in the prevalence of autism through time and geography, (2) The emergence of Asperger's syndrome as a form of autism, (3) The apparent difficulty in finding a single broad model to explain autistic behavior, etc. There is some overlap between this theory and the view that autism is just a 'way of being' or a form of 'neurodiversity'. There are also some similarities between this theory and the view that autism is a 'blanket term'.


Some people, including some people diagnosed with Asperger syndrome, argue that Asperger syndrome is a social construct and that, as a category claimed to have a clearly defined neurobiological basis, Asperger syndrome may be analogous to a host of other psychiatric labels such as ADHD, criticized by psychiatrists such as Peter Breggin and Sami Timimi; obsessive compulsive disorder; and clinical depression, much promoted by the mental health and pharmaceutical industries. 


All the behavioral traits associated with autism and Asperger syndrome occur to varying degrees in the general population. People diagnosed with either condition vary widely in terms of intellectual, professional, and social performance, range of interests, loquacity, conformity, and hypersensitivity. Those who support the social construct theory state that no scientific proof exists of a link between severe Kanner's type autism and the "geeky" and slightly quirky attributes of so many in our society, and suggest that many of the typically "Aspergian" characteristics are merely on the introverted or socially less-capable end of the normality spectrum.


Dr. Tony Attwood notes a strong association between certain types of interests and Asperger syndrome (AS).  In a talk for partners of people with AS in 2000 he illustrated what he describes as the "courtship" phase of AS by reference to Star Trek conventions, calling them "reunions for people with Asperger's" -- a classification he also extended to train spotters in the UK similarly characterised [link].  These statements have been repeated since.


Although clearly intended as illustrative of a class of readily-identified behaviours, these statements give to some the impression of being a mass diagnosis of a pervasive developmental disorder merely because they are fans of a particular television program or are rail hobbyists. Attwood is clear that it is focus on the interest itself over and above the people who share that interest which he considers as a marker; nonetheless, these remarks have proven unpopular with some "trekkers".#redirect 



Proposed causes




For more details on this topic, see Heritability of autism.


Current genetic findings are consistent with a neurodiversity model, particularly since alleles involved are not rare mutations.




This theory proposed by Simon Baron-Cohen is also consistent with a neurodiversity or social construct model.



Footnotes


  1. ↑  PMID 12039606
  2. ↑ 
  3. ↑ 
  4. ↑  PMID 15264498
  5. ↑  PMID 16272115
  6. ↑ 
  7. ↑   [Online PDF version from autismandcomputing.org.uk]
  8. ↑ 
  9. ↑ 
  10. ↑ 
  11. ↑   ([abstract])
  12. ↑ 
  13. ↑ 
  14. ↑ 
  15. ↑ 
  16. ↑ 
  17. ↑ 
  18. ↑ 
  19. ↑ 
  20. ↑ 
  21. ↑ 
  22. ↑  PMID 12949291
  23. ↑ 
  24. ↑ 
  25. ↑ 
  26. ↑ 
  27. ↑ 
  28. ↑ 
  29. ↑ 
  30. ↑ 
  31. ↑ 
  32. ↑ 
  33. Sue Bennett, Autism Immunization Pol, url=http://www.autismcoach.com
  34. Mark Geier, M.D., Ph.D., David A. Geier, B.S.| title=American Physicians and Surgeons, March 10, 2006
  35. Robert Kennedy, Jr., Autism Epidemic, Rolling Stone Magazine, June 14, 2006.
  36. ↑  D'Adamo, Peter J. and Catherine Whitney. Eat Right for your type: Complete Blood Type Encyclopedia. New York: Riverhead Books. 2002.
  37. ↑ Horvath K. et. al. Improved social and language skills after secretin administration in patients with autistic spectrum disorders. Journal of the Association for Academic Minority Physicians. 1998, 9:9-15.


References








See also


* Autism


* Conditions comorbid to autism spectrum disorders


* Heritability of autism











Pervasive developmental disorders / Autistic spectrum


 Diagnoses

Autism > Asperger syndrome | Autistic enterocolitis | Childhood disintegrative disorder | Conditions comorbid to autism | Fragile X syndrome | Rett syndrome | PDD-NOS | Sensory Integration Dysfunction | Multiple-complex Developmental Disorder


Controversy

Andrew Wakefield > Incidence | An epidemic? | Autism rights movement | Biomedical intervention | Causes | Chelation | Generation Rescue | Heritability | Neurodiversity | Refrigerator mother | Therapies


 See also:  List of autism-related topics






 





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