Autism spectrum disorders (ASDs) represent a range of brain disorders that are characterized by restricted patterns of behavior and impairments in social communication and interactions. These disorders share common origins and features, but are classified as spectrum disorders because symptoms and severity vary among individuals.

Symptoms/behaviors of ASDs can range from mild to severe, and may seem to appear gradually or suddenly. Atypical development may be observed from birth, or more commonly, become noticeable during the 12- to 36-month period. Symptoms include:

• Social Deficits - Children with autism have difficulty in social interactions. They may avoid eye contact and interactions with people and resist or passively accept attention. They are often unable to read social cues or exhibit emotional reciprocity. Thus, they are unable to predict or understand other peoples’ behavior. They may also have difficulty controlling emotion, may be disruptive or aggressive at times, or may lose control, especially when frustrated or presented with a new situation or environment. Head-banging, hair-pulling and arm-biting may occur.
• Communication Difficulties - Communication skills are affected in children with autism, but difficulties vary. Some children may have good basic language skills, but exhibit difficulty initiating or sustaining conversations, such as not giving others the opportunity to respond. Others may experience delays or regression in language development; still others remain mute or may use language in unusual ways, such as repeating a phrase, or parroting what they hear (echolalia). Body language is also often hard to read in children with autism. Facial expressions, tone of voice and gestures often do not match verbal content and emotions. They have difficulty expressing what they want or need. They may also appear deaf, not responding to their names or attempts at conversation.  
• Repetitive Behaviors - Patterns of behavior, interests and activities may be restricted, repetitive or stereotyped. For example, a child may spend long periods of time arranging specific toys in a particular manner, rather than playing with the toys. Intense preoccupation with certain topics, such as obsessively studying maps, may also be seen. Odd repetitive motions, either extreme or subtle, such as arm-flapping, freezing, rocking back and forth or walking on their toes may also occur. Often, people with autism demand consistency in their environment. A minor change in routine may be tremendously upsetting.
• Sensory Difficulties - In children with autism, the brain seems unable to balance the senses appropriately. Many children with autism are highly attuned or even painfully sensitive to certain sounds, textures, tastes or smells. Some seem oblivious to cold or pain, but react hysterically to things that wouldn't bother other children. In some people, the senses are even scrambled. For example, touching a certain texture may induce a gagging response.
• Unusual Abilities - In rare cases, some children with ASDs display remarkable abilities, such as drawing detailed, realistic pictures at a young age or playing an instrument without training. Some can memorize difficult lists of items, such as statistics or names (this is called islets of intelligence or savant skills).

Rett syndrome, often considered an ASD, is a genetic disorder almost exclusively found in females. After early neurotypical development, autism symptoms begin to develop between 6 and 18 months, which typically include shunning social contact, cessation of talking, unique motor behaviors, and a regression in skills. A single gene mutation has been identified as a cause of Rett syndrome, a finding that may enable researchers to develop improved diagnostics, earlier interventions and better treatments for the condition.

ASDs are usually evident by the age of 3, though diagnosis may be made as early as 12 to 18 months, and as late as 4 to 6 years (or later). According to the Center for Disease Control (CDC), about 1 in 31 U.S. children have an autism spectrum disorder. ASDs are three to four times more common in boys than in girls. However, girls with these disorders tend to have more severe symptoms. Some children will need ongoing supervision, while others, with the right support, pursue higher education and have fulfilling careers. ASDs affect people of all racial, ethnic and socioeconomic groups.

There are still no biological tests to detect autism. But scientists are hopeful that advanced imaging techniques and differences in blood levels of proteins in affected vs. unaffected children may have implications for diagnosis. Already, improved diagnostic procedures have allowed clinicians to diagnose children at a younger age.

Formal diagnosis involves parental input and structured and systematic screening instruments, such as the Modified Checklist for Autism in Toddlers (M-CHAT) and the Autism Behavioral Checklist (ABC) for older children. The Childhood Autism Rating Scale (CARS) and the Autism Diagnostic Inventory-Revised (ADI-R) are used, as well. These tools measure the prevalence of symptoms. Symptoms may be present from birth, or may occur after months of normal development. However, no two children with these disorders behave precisely the same way.

Between 18 months and 36 months, symptoms may include, among others:

• Limited pretend play
• Lack of pointing to demonstrate interest
• Reduced gaze following

In children with autism between 2 years and 3 years of age, the following features, among others, may be observed:

• Communication difficulties
• Socialization deficits with caregivers
• Perceptual hypersensitivity

Some combination of genetic, biological and environmental factors is believed to cause ASDs. Researchers are exploring a growing list of validated "risk genes," in which DNA variations, both common and extremely rare, are believed to contribute to the development of these disorders, as well as several brain regions that have been linked to the disorders. Abnormal brain development during the first months of life is being studied to determine if structural abnormalities, such as in the mirror neuron systems, may be caused by genetic and/or environmental factors. Researchers are also exploring the effects of genetic imprinting, in which a gene’s expression is determined by the parent who donates a particular gene copy. Certain neurotransmitters may function abnormally in ASDs. Scientists are also exploring the possibility that a faulty immune response, elevated concentrations of certain proteins in the blood at birth, dysregulation of specific neuropeptides, or major stress during pregnancy may trigger biological processes that contribute to causation.

There is no one treatment for ASDs. Many experts believe that early interventions increase the chance of better outcomes. Treatments generally address both cognitive and behavioral functioning. They may include a combination of medications (for challenging behaviors), behavioral therapy, psycho-education, family support groups, educational interventions, speech and language therapy, occupational therapy and specialized training to develop and improve acquisition of necessary skills.  New research results are continually providing occasion for considering the best modes of treatment and the most promising pathways leading to future treatments.  Small-RNA biology, for example, is providing a path to potential development of therapies that address perturbations in the developing brain, something that no existing treatment (for any brain-based disorder) can address.