Autism is the name of a disorder affecting brain development. It is one of a group of disorders called autism spectrum disorder (ASD). Asperger syndrome, atypical autism and childhood autism are kinds of autism spectrum disorders.[1]

ASD is a condition that affects the way a person relates to their environment. The word spectrum is used because not all people with autism have the same traits and difficulties. Some people find interacting more difficult than others. Autism may be very apparent in someone or they may show no outward signs of it. The main areas of difficulty are in social interaction, verbal and nonverbal communication and restricted or repetitive behaviors and interests. In most cases of autism, motor communication {doing things} is affected. All these signs develop in the child's first two to three years of age.[2]

People who have autism find it difficult to act in a way that other people think is "normal". They may find it difficult to talk to other people and to look at other people. Some people with autism do not like being touched. A person who has autism can seem to be turned inwards. They may talk only to themselves, rock themselves backwards and forwards, and laugh at their own thoughts. They might not like any type of change and may find it very difficult to learn a new behaviour like using a toilet or going to school.

Autism is caused by the way that the brain develops, both before and after a baby is born. About one in every 160 children has an autism spectrum disorder.[3]

The word “autism” comes from the Greek word “autos”, meaning “self.” The term describes conditions in which a person is removed from social interaction—hence, an “isolated self”.[4] The term "autism" was first used by a psychiatrist named Eugen Bleuler in 1911 to describe one group of symptoms of schizophrenia.[5] Sigmund Freud considered this idea and thought it was related to narcissism.[6]

Three decades later, researchers in the United States began to use the term autism to describe children with emotional or social problems. Two researchers by the name of Hans Asperger and Leo Kanner were the pioneers of the research study for autism in the 1940s.

In 1943 Leo Kanner (a doctor from Johns Hopkins University) did a study of 11 children. The children were very intelligent. He found out that they had difficulties such as changing environments, being sensitive to certain stimuli, having speech problems and allergies to food. Later he named the children’s condition “early infantile autism”.,[7] now called autism.

In 1944 Hans Asperger studied separately a group of children and found very similar conditions. The children in Hans Asperger's group did not repeat words and they had no speech problems like Kanner's did. However, the children did have problems with fine motor skills such as holding a pencil. The children he studied seemed to be clumsier than other children. They also had “[...] a lack of empathy, little ability to form friendships, one-sided conversation, intense absorption in a special interest and clumsy movements”.[8] Hans Asperger described a "milder" form of autism, his discovery is now called Asperger syndrome.[8]

In 1943 and 1949, Kanner described the children he studied in scientific papers. In these papers, he wrote that he thought the children's parents were not loving them enough. He wrote that this might be part of the reason why the children had autism.[9][10] For example, in 1949 he wrote that the children's parents showed no warmth, or love, to their children.[10] He thought the parents were so "cold" that he compared them to refrigerators:

“[The children] were left neatly in refrigerators which did not defrost. Their withdrawal seems to be an act of turning away from such a situation to seek comfort in solitude”.[10]

This idea became known as the refrigerator mother theory. For decades parents were blamed for causing their children's autism by not loving their children enough.[11] By now, we know this is not true.[12]

Schizophrenia and autism were linked in many researchers’ studies. Only since the 1960s, medical professionals began to have a separate understanding of these two disorders. Since 1980, Kanner’s so called early infantile autism is listed in the Diagnostic and Statistical Manual of Mental Disorders (DSM). Precisely because of the vague distinction between schizophrenia and autism, the DSM came out with a more accurate definition of autism in 1987. Henceforth, early infantile autism is called autism disorder. Furthermore, for the first time the DSM introduced standardised criteria to diagnose autism. The fourth edition of the Diagnostic and Statistical Manual of Mental Disorders expanded the definition of autism and included milder cases of autism. But especially the Asperger’s syndrome was added in 1994. With the release of the fifth edition of the DSM in 2013 the subtypes of autism are summarized into the general term Autism Spectrum Disorder (ASD). Individuals are now diagnosed on an autism spectrum with varying levels of intensity (mild, moderate and severe).[13]

Different studies resulted in different numbers of the frequency of autism spectrum disorders. One study stated ten cases of classical autism, 2.5 cases of Asperger's syndrome and 15 cases of mild autism (PDD-NOS) in 10,000 people - tendency: increasing.[17] Other sources speak about 60 autism spectrum disorder cases in 10,000 people.[18] However, the number of autism cases is not equal in men and in women. Here, the results of studies vary highly. Researchers in general say that 3-4 men are diagnosed for every woman that is diagnosed. This ratio decreases for severe cases to 1:1. It increases for high-functioning cases and in Asperger's syndrome reaches a ratio of 8:1.[19] Recently, the awareness has increased that this ratio may be so high because studies are simply missing female autistic people.[20] This could be because tests for autism typically focus on male autism traits.[21] Another possible explanation is that autistic females may be better at adapting to social expectations and hiding their social problems.[21] Studies have suggested that the brains of autistic females may rather be like neurotypical men’s (non-autistic men) brains of the same age.[22] These could be reasons why it is not so easy to realise whether a woman is autistic - and therefore, why more men than women are diagnosed.

Autism spectrum disorders (ASD) are seen or diagnosed more often in males than females.[23] The ratio is near one female for every four males diagnosed. But there is evidence that females may be diagnosed later than males. Researchers have argued whether there may be a gender bias playing a role in girls and women being underdiagnosed or being diagnosed late.[24] Although males may have autism spectrum conditions more often, females show different symptoms of autism than males. Autistic females also have different behaviors.[24]

Over the past years, individuals have been using the terms "autism" and "autism spectrum disorder" like they mean the same thing. Autism is a spectrum disorder. This means that some people who have autism are only mildly affected. These people may go to regular schools, go to work, and have partners and families. Some people are affected worse than others. These people may be able to take care of most of their own needs at home like dressing and getting food, but not be able to have a regular job or travel alone. A person who has severe autism may need to be cared for all their life.[25] Few people with autism are extraordinarily gifted or talented. These people are said to have savant syndrome.[26] They are often very good at just one thing in particular, like mathematics, playing the piano or remembering football scores.

The overall category of the Autism Spectrum Disorder is called Pervasive Developmental Disorder. The name describes medical conditions with developmental problems in a number of fields. In most cases, when referring to the Autism Spectrum Disorder, we are referring to the most common disorders:[27]

Additionally, only one or two of the three categories (social interaction, communication and behaviour) are affected

The different categories, the so-called “International Classification of Diseases” (ICD), are defined by the World Health Organization. As shown in the table, the diseases vary in several points. These are the age of onset, social interaction, communication and behaviour. An individual belongs to a certain category, depending on the areas of impairment. All three may seem similar in symptoms, yet are not the same. Still, people within one group show similar symptoms. The groups can be used to search for an underlying cause of the disease and to provide a better treatment.[25]

Scientists do not know exactly what causes autism. There may be many different causes for the different types of Autism Spectrum Disorder.[28] Scientists do know about some things that make a person more likely to have an Autism Spectrum Disorder.

The autism spectrum disorders are highly heritable disorders.[18] This means that it is very likely (over 90%) that the child of an autistic person will also be on the autism spectrum. The reason for this are certain genes. These genes are linked to autism and are passed on from a parent to the child. Already Leo Kanner and Hans Asperger noticed that fathers of autistic children often preferred being on their own over being with people. Therefore, Kanner and Asperger suspected a genetic cause. Studies with families with a child on the autism spectrum were done to investigate this theory. They found that sometimes the children’s parents (fathers as well as mothers) also show social difficulties, shyness and problems with understanding contextual information when talking to someone. Some studies have found this in only 10 out of 100 families, some in as much as 45 out of every 100 families.[17]

Other than the studies done on children who had autistic parents, recently a couple of studies were done on children who either had a sibling or a twin showing autistic signs. Similar to the outcomes in the autistic parents studies, most children having autistic siblings/ twins were found out to be showing autistic signs. According to a recent study, around fifty percent of infants with autistic siblings showed some kind of atypical behaviour, around one forth of them showed delays and deficits in achieving infancy milestones and around 17% of all were later diagnosed with ASD (Autism Spectrum Disorder).[29]

Moreover, twin studies showed that it is much more likely that identical twins are both on the autism spectrum than that non-identical twins are both on the autism spectrum. Identical twins have nearly the same DNA. Therefore, it is highly probable that they are either both autistic or both not autistic. Non-identical twins share only half of their genes which makes it less likely that they both have the disorder. Scientists have shown that the recurrence risk (the likelihood that a child is on the autism spectrum if it has a sister or a brother that is autistic as well) is 20 to 80 times higher than the probability for having the disorder in the average population.[30]

However, it is not a single gene that increases the risk for autism spectrum disorders. Several genes have been linked to the disorder. All of the identified genes can in sum only explain one or two out of every ten autism cases. None of the genes that have been found to play a role in autism can explain more than one out of every 100 cases.

The genetic influences include:[19][31]

The affected genes influence:[32]

Researchers have not found a single neuronal correlate for autism spectrum disorders, i.e. no abnormal functioning of the brain is the only cause of autism. Nevertheless, scientists found some differences between the brains of autistic people and the typical human brain. These differences lie in the anatomy of the brain, the activity in certain brain regions as well as in the connections between brain regions. It is a general tendency that autistic people use the same brain regions as other people but show different activity. In some areas the activity is less, in others it is stronger. However, this may only be true for male autists. Throughout the last years, studies have shown that brains of autistic women might be like normal men's brains.[22]

Some researchers grouped autistic people's difficulties into three main areas in order to investigate their neuronal basis.

Researchers say that building a Theory of mind is one of the main problems for autistic people. This makes it difficult for them to interact with others. Problems in social interaction are probably worsened by low preference for social stimuli, such as faces. This tendency has been found in studies tracking the person’s eye movements[33] and in EEG studies. EEG studies showed lower than normal activity in the fusiform face area (FFA), a brain region that is usually active when seeing faces.[34] However, the results of other studies could not show this.

Also, scientists measured brain activity of people on the autism spectrum with fMRI while they were thinking about their own emotions. They found activity in the same brain regions as in non-autistic people. The difference was that some regions which are important for thinking about oneself and emotions (especially the anterior insula) were less active in autistic people.[35] Other brain regions were much more active. These findings may explain the difficulties people with autism experience when trying to understand complex facial expressions and emotions (such as shame, jealousy).

People on the autism spectrum show a lower ability for executive function. Executive function means physical, emotional and cognitive self-control. This includes planning actions, focusing, shifting attention and flexibility of behaviour and thinking. Autistic people's ability can improve but it will remain below non-autistic people's ability in executive function.

Problems with executive function are probably caused by large networks in the brain.[36] Grey matter and white matter irregularities have a negative influence on the way different brain regions work together (functional integration).[37] A smaller corpus callosum leads to abnormalities in working memory (an active process of keeping a memory until it is needed) and planning actions.[38]

Central coherence is the ability to build wholes out of parts. It is weak in people with autism. This means that autistic people focus more on details. They cannot build wholes out of them. Not being able to pay attention to wholes results in difficulties with perception and language. Therefore, people with autism usually need more time for dealing with information coming from their surroundings. As a consequence, they typically also need more time for responding. However, performance varies between people on the autism spectrum. Moreover, the term central coherence may include many interacting aspects. This makes it difficult to find the cause for it in the brain. Neural correlates for central coherence are not yet known.[36]

The risk for autism spectrum disorders can be increased if the mother uses thalidomide, valproic acid or drinks too much alcohol during pregnancy.[17] The risk for autism also increases with the age of father and mother at the time of pregnancy.[19]

Scientists know that parents do not cause their children's autism by not being loving enough.[11]

Scientists do know for sure that vaccines do not cause autism.[3][39][40] Vaccines do not even make a person more likely to have autism - even if they are already at a high risk for autism before they get their vaccines.[41]

In 1997 A. Wakefield and others found autism signs one month after the measles-mumps-rubella (MMR) vaccine was applied. They released a paper[42] in which they claimed that autism is caused by the MMR vaccine. However, the study had several flaws:

Also, no plausible biological mechanism could explain how the MMR vaccine leads to autism.[43] Since then many case-control studies have been done to investigate the relationship between vaccines and autism. This means, they compared a group which was vaccinated with a group that was not vaccinated but apart from that identical. They did not find MMR vaccines to be the cause of autism. Neither did they find an increased risk for autism by the vaccination.[17]

Parents also worried that thiomersal (US: thimerosal - a substance that makes vaccines and other medicines usable for a longer time) might cause autism because it contains mercury. No harm from the amount of ethylmercury in vaccines was known. Yet, vaccines for infants containing mercury were taken from the market. Nevertheless, thiomersal as a cause for autism is biologically also not biologically. Mercury poisoning triggers clearly different symptoms than autism. Still, researchers did studies about this topic. They did not find a connection between thiomersal and autism.

Finally, a third theory was suggested. It was stated that many vaccines at the same time would weaken the immune system of infants. However, autism is not a disorder that is related to the immune system. Furthermore, single and also many vaccines do not weaken the immune system.[43]

Diagnosing autism is difficult since there is no medical test like a blood test. Instead, an evaluation is made by a team of doctors and other health professionals who are experienced in autism and know the individual.[44]

A reliable diagnosis can first be given at the age of two. At the age of 18 and 24 months, children should get a check-up. If anything wrong is noticed, a further evaluation is done. In this, a team of professionals will interview the child’s guardians about the child’s behaviour and see what they are like in different settings. This may also include behavioural or physical assessments as well as intelligence tests or developmental tests. A good, detailed, history of the child is often very useful in receiving a diagnosis.[45]

Adults can be diagnosed in adults as well as children. This can be difficult because autism has symptoms that can overlap with other disorders, such as OCD, that may have appeared by adulthood. An expert will usually ask the adult about concerns, challenges in life (such as socially or behaviourally) as well as standardised testing in these areas. They also often ask for a developmental history.[46]

In 2013, the American Psychiatric Association published the fifth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-V). In order to be diagnosed with autism, a person must fulfill two standardized criteria. It is important that individuals must show symptoms from early childhood, even if those symptoms are recognized later. These symptoms have to limit everyday functioning. Additionally, these symptoms cannot be explained by an intellectual disability or a developmental delay.[47]

Autism Spectrum Disorder is characterized by difficulties in social interaction, verbal and nonverbal communication and repetitive behaviours.[47]

Autism spectrum disorder includes a wide range of symptoms, skills and levels of disability. Some autistic people also have learning disabilities, mental health issues or other conditions. This means that autism can also co-occur with other conditions and symptoms of the following disorders:[48]

In the DSM-V, a diagnosis of autism excludes making a formal diagnosis of other psychiatric disorders. Therefore, other mental health conditions may be undiagnosed in an autistic person, because it is impossible to make a comorbid clinical diagnosis.[48]

Since autism is a spectrum, every person with autism is different. Different treatments help different people. There are a few different categories of treatment. The main ones are medication, different therapies and diets. The treatment is fitted depending on what a person with autism needs.

It is still unclear what causes autism. There may be a few causes. At the moment, it is only possible to lower the symptoms of autism. A full recovery from autism is not possible.[49] If therapies cannot reduce the symptoms of autism, medications are used additionally.[50] Often, several medications are used at the same time to treat different symptoms of autism.[49]

Serotonin is a chemical messenger that transports signals between cells and is very important for normal function, such as with sensory perception, memory, learning and sleep, all of which are impaired in autistic people.

Researchers have not yet found a link between autism and serotonin, although they have been successful in treating autism with SSRIs, which stop cells from absorbing serotonin, meaning more is used for signals.[49]

They can be used to treat repetitive behaviour, aggression, hyperactive behaviour and outbursts of anger.[51] The SSRIs can have many side-effects. Usually the medication is better tolerated by adults than by children. Examples of SSRIs are Clomipramine, Fluvoxamine, Sertraline, Venlafaxine, Trazodone and Mirtazapine.[52]

Dopamine is a chemical messenger in the brain. It helps to do movements, release hormones and strengthen cognitive abilities. Researchers found that increasing the amount of dopamine in the brain will worsen the symptoms of autism. Substances that help to reduce symptoms of autism are the antipsychotic drugs. There are two types of antipsychotic medications. One of the types are typical antipsychotics. They block the sites where dopamine would bind to a cell. Atypical antipsychotic drugs on the other hand block the sites where dopamine or serotonin would bind to a cell.[50] Antipsychotic medicine is the most successful treatment for excitability in autism.[52] It can also help to reduce aggression, self-injury, hyperactivity and repetitive, although it may have many side-effects.[50] Originally, antipsychotic medications were used to treat mental disorders like depression, bipolar disorder or schizophrenia.[53] Examples of antipsychotic drugs are Haloperidol, Clozapine, Risperidone and Paliperidone.[52]

In the beginning, psychostimulants were only used for patients with Attention Deficit Hyperactivity Disorder. Researchers found out that they can also help patients with autism. The medication can reduce hyperactivity and inattention in people with autism. The medication can have many side-effects. Examples are Methylphenidate, Clonidine and Guanfacine.[52]

People with autism often have problems with their digestive organs like the stomach or gut. These problems could be inflammations, abdominal pain, gas, diarrhea or bacterial overgrowth. The reasons may be malnutrition, food intolerances or allergies. Specific food products causing these problems are excluded from the diet. In many cases, products containing gluten or casein, the main protein occurring in dairy products, are excluded. In many cases vitamins, minerals as well as essential fatty acids are additionally provided. A big problem is that many autistic people cannot tell that they have pain. Therefore, many problems concerning the digestive organs stay undetected.[54]

Therapy can be used to minimize distress caused by sensory overload. Individual therapy plans are created. The therapist tries to help the autistic person in many different aspects.

One part of this is sensory integration. The therapist will help the patient to make sense of different sensory inputs. For example, they may ask a child patient to play with finger paints or collect objects from a bad of dried beans.

Another part is the training of daily life activities. The therapist may help the patient to get used to things like getting dressed, eating, hygiene, shopping and financial management. These may be done one step at a time if the activity involves multiple steps, such as cooking.

Play therapy is also helpful, especially for children. It can be useful to learn about certain emotions, which can be hard for autistic people. This can also be used to help learn social conventions, such as shaking hands instead of hugging when meeting a stranger.[55]

Often animals are used to help autistic people. Most often dogs or horses are used. The people diagnosed with autism can care for these animals, pet them and, in the case of the horse, even ride on them. Studies showed that the interaction between an autistic person and animals can increase communication, reduce stress, fear, aggression and reduce the severity of the symptoms of autism.[56]

Music therapy consists of two parts: One is an active listening part. Here, the therapist is making music himself or playing music from a record. In the other part, the autistic person can make music himself like playing an instrument or singing. Music therapy will improve different aspects of communication.[57]

Here, different materials and techniques are used to draw pictures. The aim of art therapy is to make the autistic person more flexible and relaxed and to improve communication skills, self-image and learning skills. The effects of the therapy can be long lasting and transferred to the school, work or home setting.[58]

Scientific studies