Born Different: What Causes Asperger's Syndrome?
Born Different: What Causes Asperger's Syndrome?
Autism and Vaccines
High-Tech Brain Scanning
Brains in Action
A Brain Test
Too Many Males
Human Social Brains
Mind Blindness and Genes
Genetic Evidence and Autism Spectrum Disorders
Continuing the Search
Asperger's syndrome seems to have a neurological cause. There is a problem with certain structures and systems in the brain such that AS brains do not operate in the same way that neurologically typical (neurotypical) brains do. This is not necessarily a malfunction, and it is not a disease or the result of bad childhood experiences. Tony Attwood explains, “In short, the brain is ‘wired’ differently, not necessarily defectively, and this was not caused by what a parent did or did not do during a child's development.”18 People with AS have brains that may cause them to think and respond differently than normal, neurotypical brains, but that does not mean that they are abnormal, wrong, or damaged. They are just different. Most experts believe that this different way of thinking and feeling is inborn, or present from birth, and is a result of genetic factors.
Scientists have accumulated a good deal of neurological evidence about the brain differences that occur in AS in particular and in autism spectrum disorders in general. Today's medical technology allows researchers to watch living brains in action and find the areas of the brain where things seem to be wired differently.
In the news and in popular opinion, there is a great fear that certain vaccines given routinely to babies could be the cause of autism. One vaccine that has come under suspicion is the measles, mumps, and rubella (MMR) vaccine. The theory is that the measles part of the vaccine causes a kind of inflammatory disease in the intestines of some children. This disease then spreads toxins to the brain that do damage and cause autism. Many parents today are afraid to allow their children to receive the MMR vaccine because they worry that it could cause autism. However, there is no medical proof that MMR vaccinations are dangerous. Because of public concern, researchers have instituted long-term studies to look for a connection between the MMR vaccine and autism. Although the evidence may change in the future, so far no studies have indicated that autism is brought on by vaccinations.
Specific areas of the brain are responsible for controlling different functions and behaviors. The cerebral cortex is the area of the brain responsible for higher functions such as language, problem solving, thinking, emotions, reasoning, processing information, voluntary muscle control, and perceiving the environment. The cortex is a sheet of tissue, sometimes called gray matter, which is the outer layer of the brain.
The brain as a whole is divided down the middle into two equal halves called cerebral hemispheres. The hemispheres are each further divided into four lobes. They are the frontal lobes, the occipital lobes, the temporal lobes, and the parietal lobes. Scientists have identified and named the areas of the cortex and the lobes where specific functions occur. The frontal lobes are the parts at the very front of the brain. They are responsible for reasoning, speech, problem solving, and some emotional responses. The occipital lobes are at the back of the brain and are involved with vision. The parietal lobes are behind the frontal lobes and concerned with perception of pressure, pain, touch, and temperature. Below the frontal lobes are the temporal lobes. Here lies the amygdala, which seems to play an important role in emotions and feelings, as well as in memory. The amygdala is responsible for the fear that results in “fight or flight” responses and acts as the brain's emotional warning system.
Researchers can see inside people's brains and map all these structures using magnetic resonance imaging (MRI). With this technology they can compare the brain structures of typical people to people on the autistic spectrum and look for differences. An MRI is a medical test that uses a large magnet to create a magnetic field around a person's head. Then radio waves are sent through the magnetic field. A computer reads the wave signals and builds a detailed picture of the brain. Some MRI studies have shown that people with autism have differences in the frontal and parietal lobes of their brains when compared with neurotypical people. Other studies have suggested that the amygdala is smaller than normal and that its cells are smaller and more tightly packed than in typical brains.
In one study, a team of scientists led by psychiatrist Joseph Piven at the University of North Carolina compared the MRIs of thirty-eight people with autism with the MRIs of thirty-eight neurotypical people. The team discovered that almost half of the autistic people had larger brains than the people without autism. This larger size seemed to occur in certain regions of their brains, including in the frontal lobes.
Another study led by Dr. Antonio Y. Hardan at the University of Pittsburgh measured the thickness of the cortex in seventeen autistic boys and compared it with the thickness for fourteen normal boys. The cortices of the autistic boys were measurably thicker. Studies such as these suggest that true neurological differences are related to autism spectrum disorders, but no one knows yet why this is so. The differences do not show up 100 percent of the time, and scientists do not know how brain size is related to neurological dysfunction in autism. They do know, however, that evidence of brain differences shows up in almost all MRI studies of autistic people.
MRIs have also been used to identify activity in the brain as it is working or functioning. Even when areas of the brain look the same, scientists can identify the areas that function differently in autistic brains with a special kind of MRI called functional magnetic resonance imaging (fMRI). With fMRI, scientists can get an image of the blood flow in the area of the brain where activity is occurring. They can watch the brain as a person does specific tasks, such as solving math problems, looking at faces, or reading. They can see the changes in blood flow that indicate which part of the brain is being used to perform the tasks.
They can see how active that part of the brain becomes when it is required to perform those tasks. Some studies have found less activity in the frontal lobes of children with AS when they are asked to make judgments about social situations. Others have discovered that different areas of the brain are more active when people with AS are viewing images of facial expressions than the areas used by neurotypical people.
Mirella Dapretto, a psychiatrist at the University of California at Los Angeles, studied the social skills of eighteen boys with autistic spectrum disorders using fMRIs. She had them watch short cartoons of people having conversations. The boys were asked to figure out if the cartoon people were speaking sincerely or sarcastically. She compared the fMRIs with those of eighteen neurotypical boys who also watched the cartoons. The boys with autistic spectrum disorders showed less activity than normal in the frontal areas of the brain. Then she instructed all the boys to pay particular attention to the facial expressions and the tones of voice of the cartoon characters. The normal boys showed no change in brain activity. They already were concentrating on faces and tones of voice. The autistic spectrum disorder boys, however, responded to the instructions. They showed increases in brain activity as they did what other kids do naturally—notice the social cues.
Explains Dapretto: “The typically developing kids recognized and interpreted these cues automatically when trying to infer if a speaker's remark was sincere or sarcastic, so their brains were already responding appropriately. But not so with the ASD [autistic spectrum disorder] kids, who did not show activity in this area when specific instructions weren't provided.” The fMRI results provided evidence that the boys were not defective, according to Dapretto. She says that “the fact that you can ‘normalize’ activity…clearly indicates there's nothing intrinsically wrong with this region in the autistic brain.”19 They could respond to social cues if they were told to do so; they just did not do it naturally.
About four times more boys than girls are diagnosed with autism spectrum disorders. Decades ago, autism expert Bernard Rim-land pointed out that boys are just more likely to have hereditary diseases and organic damage than girls do. In this sense they are biologically weaker than girls are. Rimland's statement has been verified many times, but no one knows why it is the case. One theory involves the chromosomes that determine sex. They are called the X and Y chromosomes. Girls have two X chromosomes. Boys have an X and a Y. Many genetic traits are sex linked. This means that genes that cause defects can be on the X chromosome. (Genes for traits are very rare on Y chromosomes.) A girl, with two X chromosomes, may be protected from disease if one X chromosome has defects but the other is normal. A boy, because he has only one X chromosome, would be likely to have the disorder because his Y chromosome cannot protect him. It acts like a blank. As yet, however, no proof of genes for autism spectrum disorders on the X chromosome has been discovered.
Another theory is a social one. It suggests that girls with AS are just better at hiding their symptom than boys, so they are under-diagnosed. Perhaps they are better at imitating social skills and faking normalcy. Also, in American culture, it is more acceptable for girls to be shy, bad at sports, or to daydream. Their symptoms are not troublesome, and so they may not be referred for diagnosis by teachers and parents. Experts who argue for this theory say that AS probably really affects boys and girls equally.
Psychiatrists have a theory about why people with autistic spectrum disorders do not automatically respond to social cues. They say that several regions and systems of the brain, particularly in the frontal and temporal areas of the cortex, work together to make up what they call the “social brain.”
Some studies suggest that the amygdala is part of the functioning of the social brain, too. An organization named the Research Committee of the Group for the Advancement of Psychiatry explains, “The social brain is defined by its function—namely, the brain is a body organ that mediates [works out and makes connections about] social interactions while also serving as the repository [memory bank] of those interactions.”20 It is the social brain that most researchers believe is dysfunctional in people with AS, because of a difference in wiring.
According to psychological thought, because of the social brain, typical people develop a skill called theory of mind. Attwood explains that this “means the ability to recognize and understand thoughts, beliefs, desires and intentions of other people in order to make sense of their behaviour and predict what they are going to do next.” Experts believe that people with AS do not have an adequate theory of mind. They are lacking empathy, or the ability to put themselves in someone else's shoes. Psychiatrists also call this ability “mind reading” and describe the inability to mind read as “mind blindness.”21
Most typical people develop the ability to mind read accurately by the time they are five years old. People with AS, however, are often mind blind to some degree throughout their lives. Their theory of mind is immature or impaired, and they may even have trouble identifying and expressing their own emotions and feelings because of their mind blindness. Brain studies of adults with AS who are asked to watch social stories show less activity than normal in the areas of their brains that control theory of mind abilities. Instead of focusing on the social and emotional aspects of the stories, the brains with AS are apparently wired to pay attention to the physical, logical descriptions of what they see. They intellectually analyze situations, rather than responding with empathy to the feelings of story characters.
Neurotypical people mind read easily, without thought, and seemingly intuitively. They do this by watching facial expressions, looking into someone's eyes, listening to tones of voice, interpreting words and phrases of others, observing body language, and following the social cues that others give them. People with AS do not have the social capacity to do any of this easily. This does not mean their brains are defective and unable to respond to others at all. It does not mean they do not care about other people. As Attwood says, “The [AS] person does care, very deeply, but may not be able to recognize the more subtle signals of emotional states or ‘read’ complex mental states.”22
Understanding the neurological factors that lead to deficient theory of mind skills in people with AS is important. But knowing the effects of social brain impairments does not explain how the brains came to be wired in a different way. Most researchers and experts believe that AS has a genetic cause.
Genes are the basic units of inheritance for all living things. They are found inside the nucleus of almost every cell in the body. Genes are basically strings of deoxyribonucleic acid (DNA) that write the giant chemical book of instructions that codes for how a living being develops and functions. In human beings genes are arranged into twenty-three pairs of chromosomes. Each chromosome is made up of thousands of genes. Genes code for being a human, a mouse, or a daisy. They carry the coded instructions that tell heart cells to beat, eye cells to gather light, and brain cells to gather information. It is helpful to think of chromosomes as recipes and each gene as an ingredient. The instructions for the ingredients are spelled out by the DNA code.
Most genes and DNA are the same for all human beings, but some genetic instructions are unique to each individual. That is why people look different and have different natural abilities. It is also why some people have inherited disorders. Genes are inherited from one's parents, and each new individual receives half his or her genes from one parent and half from the other. Sometimes these genes carry slight changes, variations, or mistakes that occur when the DNA is being copied as the cells divide and new life develops. Such “typographical errors” can be passed on to the next generation, resulting in inherited diseases, or just causing differences in the way that an individual develops. Scientists believe this is the kind of process that results in AS and in autism spectrum disorders. But they do not believe that just one variant gene is responsible. They suspect that multiple genetic variations cause the neurological differences seen in AS. Finding these genes and understanding how they vary is an extremely complex task.
Researchers do have evidence that AS runs in families. In one study, it was found that about 20 percent of fathers and 5 percent of mothers have symptoms of AS when they have a child diagnosed with AS. Brothers and sisters of a person with autism are 2 to 8 percent more likely to have an autism spectrum disorder than are people without a relative with autism. When all extended family members are examined (uncles, grandparents, cousins, and so on), more than 66 percent show some autistic symptoms and characteristics. For instance, relatives may have mild language problems, be loners, or have trouble empathizing with others.
Canadian researcher Peter Szatmari is one of the world's leading experts in the genetics of autism. He is a director of the worldwide Autism Genome Project. He and his team are looking for the specific chromosome where genes for autism spectrum disorders might be found. Szatmari's team has taken DNA samples from six thousand family members in which at least one person has an autism spectrum disorder. They use a kind of DNA fingerprinting to map the genes in each individual sample and to compare the DNA variations in a search for the genetic causes of spectrum disorders. So far the Autism Genome Project has identified a chromosome named chromosome 7 as an area of particular interest, as well as DNA variations on chromosome 2 and on chromosome 11. Szatmari has said, “Not only have we found which haystack the needle is in, we now know where in the haystack that needle is located.” He says there are at least ten to twenty genes involved in autism, and he thinks that perhaps different combinations of these gene variations may be why some people have AS and others have different forms of autism. He explains about the research so far that “these findings not only tell us which chromosomes (or haystacks if you will) are involved, but where on the chromosome (or in the haystack) the genes might be.”23 As yet, however, neither Szatmari nor any other researcher has been able to identify for sure the specific genes involved in any of the autism spectrum disorders.
Researchers such as Szatmari keep working on the genetics of autism and AS because they believe that a breakthrough will come in the near future and they will be able to identify the genes that cause the disorders. When that happens, firm diagnosis of autism spectrum disorders will be possible in even young infants. And that ability will make early treatment possible so that people with autism and AS can live happier, more comfortable lives.
Szatmari, along with most other scientists, does not believe that genetic causes mean that nothing can be done to change the ways that AS brains think and respond to the world. Since AS is a developmental disorder, over time, people can slowly improve their ability to form a theory of mind and to understand the ways in which neurotypical people relate to each other. They can use their logic and intellectual abilities to figure out emotions and empathy. Although there is no cure for AS, treatment and therapy can help people to make progress in their journey toward functioning in the neurotypical world. Attwood explains that many teens and adults with AS reach “a point on the continuum where only subtle differences and difficulties remain.”24 Most people with AS do not want to give up all their differences anyway, and many experts agree that they should not. They recognize that the AS way of thinking can be valuable and positive, but people with AS may need help with “getting” the rules under which much of society operates.