Autism, or autism spectrum disorder, refers to a range of related medical conditions characterized both by challenges and strengths. Children with autism often struggle to learn social skills, face difficulties with verbal and nonverbal communication and have a tendency to engage in repetitive behaviors.
What Causes Autism Spectrum Disorder?
Caused by a complex interplay of genetic and environmental factors, autism spectrum disorder can be mild or severe, presenting only minor challenges or coming to interfere completely with the activities of daily life. The condition is far more common in boys than in girls. Autism spectrum disorder is diagnosed in around 1 in 37 boys, while it appears in about 1 in 151 girls, according to Autism Speaks.
Researchers now know that people with autism spectrum disorder are born with differences in the way their brains process information, but the condition is still poorly understood. What, in the first instance, causes these changes in brain function? Could birth injuries play a part in the story?
Do Birth Injuries Play A Role?
Like cerebral palsy, a neuromuscular disorder diagnosed in between 8,000 and 10,000 babies and infants every year, autism spectrum disorders appear to be caused by a range of factors, both genetic and environmental. It seems highly likely that one of these potential factors, for some children, involves birth hypoxia, a form of birth injury caused by oxygen deprivation during labor or delivery.
In severe cases, birth hypoxia can lead to hypoxic-ischemic encephalopathy, a severe form of brain damage. Hypoxic-ischemic encephalopathy, or HIE, is a leading cause of cerebral palsy and, in some cases, it may lead to autism as well.
Researchers Link Autism To Difficult Birth
In the first large meta-analysis of studies on the perinatal (“around the time of birth”) risk factors for autism, researchers at the Harvard School of Health found evidence that many birth-related complications appear to increase the risk for autism spectrum disorders. In the study, Hannah Gardener, ScD and her colleagues re-analyzed the data from 40 different studies, identifying a number of birth complications that were associated with autism.
High on their list, according to Dr. Geri Dawson, chief science officer at Autism Speaks, were complications associated with “hypoxia, or low levels of oxygen in the brain of the baby.” As we’ve already noted, birth hypoxia is a leading risk factor for cerebral palsy and other severe developmental disabilities. Among these complications were:
- breech birth position, which can compress the umbilical cord, cutting off the baby’s blood and oxygen supply
- umbilical cord complications
- fetal distress, a condition commonly related to oxygen deprivation
- maternal hemorrhage, which compromises blood pressure within the mother’s body, thus threatening a baby’s oxygen supply
Alongside these hypoxia-related complications, the researchers noted that children who had suffered birth injuries or perinatal trauma were also at an increased risk of developing autism. In fact, birth injuries increased the risk for autism by an extraordinary amount. Children who suffered birth injuries during labor or delivery, the study’s authors note, were around 500% more likely to develop autism spectrum disorders than children who did not suffer birth injuries.
In their paper, published in a 2011 edition of the journal Pediatrics, Gardener and her co-authors reiterated the view, shared by so many other researchers, that no single factor was sufficient to casually explain autism spectrum disorders. In an interview with the Los Angeles Times, Gardener told reporters that “having a difficult birth may amplify a child’s established genetic risk or may confer risk of the neurodevelopmental disorder all by itself.”
“The obstetrical risks factors that have emerged as significant risk factors for autism in the current meta-analysis,” the study authors write, “suggest a possible role of fetal and neonatal hypoxia.” The authors hypothesized that a sudden decrease in oxygen seemed to increase activity in a set of brain cells that work with the neurotransmitter dopamine. These same cells, the authors continue, appear to act abnormally in patients with autism spectrum disorder.
Autism: A Multifactorial Explanation
According to researchers in a 2009 edition of the Lancet, autism is “multifactorial”; in attempting to explain the disease, we’d be hopeless to point to a single cause or factor. Instead, most cases of the condition come down to multiple, interacting causes that occur together.
You can think of autism, so far as causes go, as a cake. Every ingredient, the eggs, the flour, the butter, are essential to achieving the result. All of the ingredients have to be combined together to bake a proper cake; leave the eggs out, and your cake will turn out as a dense, flat brick. But all of the other ingredients are essential, too. You can’t leave out anything.
Causally, autism spectrum disorders are similar. You need multiple co-occurring “ingredients” to bring about the condition – one or two probably aren’t enough. Genetic and environmental factors may predispose a child to developing autism, making it more likely to occur, but multiple other factors are necessary to make the thing official.
At the same time, you can substitute different risk factors for each other, just as, in baking a cake, you can substitute vegetable oil for butter and still come out with a cake. The taste may be different, but it’s still a cake. There’s no single, all-encompassing recipe for a cake. Nor is there a single, all-encompassing combination of factors that cause all cases of autism.
There are a variety of factors that can cause autism; as we’ve seen, birth injuries, and specifically birth injuries that result in oxygen deprivation around the time of birth, appear to be among these factors. Perhaps this is why people with autism spectrum disorders show such variety in the severity of the condition and its characteristics, why some are highly-functioning while others are severely-disabled.
The Genetics Of Autism Spectrum Disorder
Autism spectrum disorder is “highly genetic” in nature, though it is likely that environmental factors, including neonatal oxygen deprivation, play a role. Through the sequencing of genomes in people with autism, researchers have identified countless genes and genetic mutations that may be implicated in the condition.
Autism spectrum disorder also appears to be highly heritable, passed, through genetic information, in families. As Dr. Daniel H. Geschwind, a researcher at UCLA’s Center for Autism Research and Treatment, points out, people with autistic siblings are around 25-times more likely to have autism themselves.
In recent years, however, a bevy of new studies have called the genetic basis of autism into question. At one point, based in part on the strength of heredity studies like the one described above, researchers believed that autism spectrum disorders were almost entirely genetic in nature. New analysis has downplayed the role of genes, in favor of environmental factors, including complications suffered during birth.