Parents of children with autism usually have a few unanswered questions like “how did my child develop autism? My child was hale and healthy and had even started to speak a few words. Then, what happened suddenly?”So, is autism acquired? Could it have been prevented? Is it genetic? Can the other children also have autism? Yet, this is a question to which no deﬁnitive answers are given to them. 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 like mesial temporal lobe (inner most 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. This information, about the functioning of brain areas is obtained from PET-CT and functional MRI scan of the brain. These imaging studies allow us to study the abnormal pattern of cortical activation in autism. These studies indicate that reduced blood ﬂow to certain areas of the brain could lead to reduced functioning of those areas.
Research has also help us know that just as there is no one type of autism in the same way there is no one cause of autism. Over the last five years, scientists have identified a number of rare gene changes or mutations which have been associated with autism. A small number of these are sufficient to cause autism by themselves. However, most cases of autism seem to be caused by a combination of autism risk genes and environmental factors influencing the early brain development.
Below mentioned are a few possible causes of autism:
Genetics - Is autism heritable?
Genetic factors are thought to be one of the most significant causes for autism spectrum disorders. It was estimated that genetics could explain the occurrence of autism in over 90% of patients, however the studies later proved that this was an over estimate. In a twin study that was conducted it was found that many of the non-autistic co-twins had learning or social disabilities. Thus explaining the occurrence of autism, purely on the basis of genetics is a very complex task. As how, different genes interact with each other, how much penetrance (how deeply are they responsible for a certain feature or characteristics), what defect is there in the gene, environmental triggers, and many other factors finally decides, whether a child is or would be autistic or not.
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.
Prenatal and perinatal risk factors could be one of the most important environmental triggers for autism. There are several prenatal risk factors which could cause autism, like advanced age of either parent, diabetes, bleeding, and use of psychiatric drugs in the mother during pregnancy. A child’s risk of developing autism has also been associated with the age of his or her parent at birth. The biological reasons for this are unknown: possible explanations include increased risk of pregnancy complications, increased risk of chromosomal abnormalities, spontaneous mutations, etc.
Environmental agents like teratogens can cause birth defects. Some agents that are theorized to cause other birth defects have also been suggested as potential autism risk factors, although there is little to no scientific evidence to back such claims. All known teratogens appear to act during the first eight weeks from conception, and though this does not exclude the possibility that autism can be initiated or affected later, it is strong evidence that autism arises very early in development.
Autism is associated with some perinatal and obstetric conditions. A 2007 review of risk factors found associated obstetric conditions that included low birth weight and gestation duration, and hypoxia during child birth. This association does not demonstrate a causal relationship. As a result, an underlying cause could explain both autism and these associated conditions.
A wide variety of postnatal contributors to autism have been proposed, including gastrointestinal or immune system abnormalities, allergies, and exposure of children to drugs, vaccines, infection, certain foods, or heavy metals. The evidence for these risk factors is anecdotal and has not been confirmed by reliable studies. The subject remains controversial and extensive further searches for environmental factors are underway.
Other maternal conditions:
Prenatal stress consisting of exposure to life events or environmental factors that distress an expectant mother, have been hypothesized to contribute to autism, possibly as part of a gene-environment interaction. There have been animal studies which have reported that prenatal stress can disrupt brain development and produce behaviors resembling symptoms of autism.There also have been studies which report that prenatal high testosterone levels in the amniotic fluid and prenatal exposure to ultrasound waves have been fleetingly associated with autism, though no substantial evidence to support it has come through.
Diabetes in the mother during pregnancy is a significant risk factor for autism apart from that obesity and hypertension during pregnancy are also associated risk factors. How they contribute to development of autism though is still not clear.
Thyroid deficiencies in the first 8-12 weeks have been postulated to produce changes of autism. Thyroxine deficiencies can be caused by inadequate iodine in the diet, improper absorption or possible environmental agents such as flavonoids in food, tobacco smoke, and most herbicides. However, this hypothesis has not been proven yet.
Mercury poisoning has been thought to be one of the causes of autism. This cause has not been very well validated, since the features of mercury poisoning and autism do not match and evidences so far are indirect. A meta-analysis published in 2007 concluded that there was no link between mercury and autism.
The MMR vaccine theory of autism is one of the most extensively debated theories regarding the origins of autism. The Centers for Disease Control and Prevention, the Institute of Medicine of the National Academy of Sciences, and the U.K. National Health Service have all concluded that there is no evidence of a link between the MMR vaccine and autism. As diseases like measles can cause severe disabilities and death, the risk of a child’s death or disability due to not vaccinating a child is significantly larger than any minuscule risks due to vaccinating.