Causes of Autism
Autismis a class of neuropsychiatric and neurodevelopment disordersclassified under autism spectrum disorder (ASD). In most cases, itaffects language, social interactions, IQ and emotions among othersand causes pervasive impairments. The exact cause of autism hasremained unclear despite intense research to understand thisneurodevelopment disorder. The main hypothesis pursued by severalscholars claims that both genetic and environmental factors play apart in causing autism (Yirmiya & Charman, 2010). This is to meanthat some children are born already afflicted with the disorder as aresult of genetic disposition and others develop autism afterexposure to different environments postnatal or prenatally as thispaper seeks to portray using current relevant literature.
Geneticfactors contribute 10-11% of autism cases globally (Geschwind, 2011).This genetic involvement has been identified through three main studyapproaches: comparison of monozygotic twins (MZ) and dizogotic twins(DZ), family studies comparing the rate of autism in differentdegrees of relatives compared to nonrelatives and studies of raregenetic syndromes with comorbid autism diagnosis on generalpopulations. Results have shown that MZ twins have higher chances ofdeveloping ASD together than DZ twins whose shared genetic componentis relatively lower than the MZ twins. First degree relatives alsoshow higher likelihood of developing ASD than the rest of thepopulation. In fact, in some families with autistic members, othermembers have shown signs of supressed ‘autistic traits’ andtendencies such as repetitive behavior and social exclusion(Landrigan, 2010).
Thetwins study showed that the shared environment from conception inboth DZ and MZ twins only explained about 90% of the cases. The other10% was attributed to genetic causes (Geschwind, 2011). Severalchromosomes such as 7q, 15q and 2q have been associated with ASD. Agene known as SHANK3 has been found to cause synapse formationconsistent with ASD. Other genes such as CNTN4 have been linked withduplications, deletions and CNVs (copy number variants) associatedwith ASD. Nonetheless, the genetic approach does not discredit theenvironmental influence hypothesis but acknowledges the genetic role(ibid)
Studieson environmental causation take two major approaches: prenatal(influences during pregnancy) and post natal (influences afterbirth). Landrigan (2010) explores both environments and notes thatthe prenatal environment studies largely center on various componentsnamely: thalidomide, misoprostol, and valproic acid infections onthe mother (rubella) and chemical exposure to the motherspecifically to insecticides with chlorpyrifos. A mother’s exposureto these chemicals means indirect exposure of the unborn child to thesame chemicals. Clinical and epidemiological studies have linkedthese chemicals to autism. In one study in Brazil, four out of sevenchildren (57.1%) with ASD were discovered to have been exposed toMisoprostol through their mothers before birth (ibid). In anotherstudy in Sweden also discussed by Landrigan, thalidomide exposure topregnant women was shown to play the same role. From a population of100 thalidomide embryopathy cases, at least four cases were diagnosedwith ASD and further analysis on concomitant somatic malformationsshowed critical exposure time to be 30-24 days after conception(ibid).
Thepostnatal environment and its role in causing autism assumes infantsget exposed to harmful chemicals with developmental neurotoxicitydirectly on their own or through the mother via breast feeding(Yirmiya & Charman, 2010). Either way, the impact is the same onthe infants. Generally, there are over 3000 synthetic chemicals thatare suspected of causing developmental neurotoxicity (Landrigan,2010). They are found in every day products such as detergents, food,air and water and have been increasingly detected in blood and urinesamples of ordinary people. The chemicals include lead, manganese,arsenic, ethyl alcohol, methyl mercury among others. Such heavymetals not only cause autism but have also been linked to low IQ(ibid).
Previously,some vaccines were suspected of increasing the risk of autism ininfants. These fears were triggered by clinical observations in theUS and UK which showed that autistic symptoms appeared following somespecific vaccinations. In the US, ethyl mercury, which is used in thepreservation on a range of vaccines, was suspected while in the UKthe measles–mumps–rubella (MMR) vaccine was suspected.Interestingly, MMR infections in pregnant mothers have been proven todirectly contribute to autism in the unborn children. Nonetheless,the fears over the contribution of these two vaccines on infants havebeen settled through clinical trials which registered no evidence(Geschwind, 2011).
Othercauses and future research
Otherfronts that researchers are pursuing to understand the causes ofautism include complications during delivery, contribution of otherdiseases such as tuberous sclerosis and untreated phenylketonuria(PKU). For others, the genetic front is being targeted through asuspected fragile x syndrome. All these views are still beingresearched and no concrete evidence has been developed to show thecontribution to autism so far. Future research may also target MRIscans of the brains of affected individuals to understand how best torespond to existing cases informed by the fact that various parts ofthe brain control certain functions such as language, speech andsocial function which are mostly affected by autism (Geschwind,2011). MRI scans can detect how sections of the brain respond duringvarious functions and detect any anomalies and possible remedies.
Understandingclearly the causes of autism is the best way of addressing the risingcases of autism. Although improved diagnostic methods can beattributed to the increased cases, it is necessary to acknowledgethat increased exposure to harmful chemicals with developmentalneurotoxicity has also played its role. Understanding the causes ofautism better will allow preventive measures to be developed. Thepaper has clearly demonstrated that children can be born with autismor it can develop later after birth. For those born with it, it candevelop soon after conception from genetic influences, or develop itas a result of environmental influences in the womb or even acquireit after birth through environmental influences. However, this hasnot ruled out other causes as current research seeks to understandthe syndrome better.
Geschwind,D. (2011). Genetics of autism spectrum disorders. Trendsin Cognitive Science.
Landirgan,P. (2010). What causes autism? Exploring the environmentalcontribution. Current
Yirmiya,N. & Charman, T. (2010). The prodrome of autism: early behavioraland biological
signs,regression, peri-and post-natal development and genetics. Journalof Child Psychology and Psychiatry,51, 432-458