Unraveling the Mysteries: What Causes Autism?

Genes play an extremely important role in autism. Experts believe that the heritability of autism sits somewhere between 80 and 90 percent. In cases of identical twins, on the off-chance that one twin has autism, and the other does not, the one without the condition often has other learning or social disabilities. Over the years, scientists have found dozens of genes with strong links to autism and hundreds more that could be connected. Though some cases of autism are inherited through parental DNA, the vast majority of cases occur sporadically—despite the high heritability of the condition. For this reason, many experts refer to these genes as "risk factors" and believe that it is environmental factors that then influence whether or not a person will develop autism.

Studies show that several environmental factors could increase the risk of autism. Many of these involve the pregnancy or the very early stages of infancy. Premature birth and low birth weight also increase the risk. A few research efforts have pointed to air pollution exposure during pregnancy or early infancy leading to autism, but this requires more study. Similarly, diesel exhaust, microplastics, alcohol, smoking, illicit drugs, pesticides, and heavy metals have all also appeared in lists as potential culprits. Ultimately, it is nearly impossible to identify every environmental factor because there are so many variables.

Scientists have frequently indicated brain structure differences as influences in the development of autism. The specifics of this are complex, and the mechanisms often vary. For example, some experts think that autism is a form of autoimmune disease where antibodies attack the brain during development. Others believe that thyroid issues during pregnancy impact the infant's brain. The areas of the brain that are most often related to autism include:

• Amygdala - responsible for emotional responses
• Basal ganglia - help regulate automatic movement
• Brain stem - helps transfer messages between the brain and body
• Cerebellum - assists with balance, body movements, speaking muscles, and motor activity
• Cerebral cortex - responsible for higher mental functions, movement, behavioral reactions, and perception
• Corpus callosum - allows the hemispheres of the brain to communicate
• Hippocampus - responsible for retaining information and memories

During pregnancy, many different factors could influence the chance of the infant developing autism. Infection, high blood pressure, or diabetes are all common issues during pregnancy, and each may be a risk factor. Even prenatal stress could be a factor. Experts realized that many prenatal issues involve inflammation of some kind, potentially revealing that inflammation is truly responsible.

One of the most persistent myths about autism is that vaccines can cause autism. This is completely false. The brain development consistent with autism is visible in scans even while the child is in the womb, before the administration of any vaccines. Some people believe that giving too many vaccines in too short a time is responsible for autism. This thought has no scientific basis and is biologically implausible. In the few studies indicating a link between vaccines and autism, the vast majority of authors have rescinded their interpretations, and the journals often retract the papers. Investigations of these studies have consistently found issues of data manipulation or outright fraud to assert the link between vaccines and autism. High-quality, peer-reviewed studies consistently find no causal relationship between the two. Finally, the preservative thiomersal has been the focus of misinformation. Since 2002, this ingredient has appeared in only a single childhood vaccine, and rates of autism have not diminished. International scientific and medical bodies have overwhelmingly rejected the idea that thiomersal causes autism.

Because of its high heritability and genetic linkage, many people assume that autism runs in families. However, the truth is a bit more complicated than that. A family history of autism does indicate a greater chance of a child developing it, as well. The same is true, though, of depression, schizophrenia, and obsessive-compulsive disorder. Some researchers have proposed the theory that there are two methods of autism development: inheritance and spontaneous development. The spontaneous form seems to be more common in the general populace.

Children can start to show signs of autism at an extremely early age—usually within the first year. That being said, it is worth pointing out that many children show some of these signs, and parents should not use them to diagnose their child. By 12 months old, a child with autism might not babble, respond to verbal cues, react to waving or peekaboo, or look at objects that someone else points to. Within the next few months, the child might not say a single word or participate in pretend play. In general, slow language development is one of the major signs of autism.

Parental age is potentially a major risk factor for autism. As the parents age, the risk for genetic mutations increases dramatically. This is particularly true for sperm, as genetic mutations in sperm gradually accumulate over years. Several studies showed that paternal mutations were the primary drivers of autism development rather than the maternal mutations. Additionally, the relationship between mutations and age was more direct in the male figure.

From the health and age of the parents to the environment during pregnancy, there are far too many considerations to point to a single cause for autism. Instead, the condition stems from a deep and complex web of interconnecting factors. With more time and research efforts, scientists will allow for a better understanding of this web. This will allow more accurate predictions of autism development and enable earlier, more accurate diagnoses.

As with any complex medical topic, misconceptions about autism will continue to exist, and new ones will appear. People worry for their children and wish for them to be healthy. A simple answer that a specific factor causes autism is far easier to comprehend than the complex truth. Though many individuals feel concerned that the rates of autism are increasing, this is due to a better understanding of the condition and more accurate diagnostic measures.