Here, we propose to take advantage of this diversity in autism genetics by examining mouse models of multiple mutations associated with ASD. The resulting imaging findings will help to group the autism models studied into a small number of distinct clusters, which can be rationalized based on either behavioural or genetic differences.
Imaging studies of people with ASD have found differences in the development of several regions of the brain. Studies suggest that ASD could be a result of disruptions in normal brain growth very early in development.
These disruptions may be the result of defects in genes that control brain development and regulate how brain cells communicate with each other. Autism is more common in children born prematurely. Environmental factors may also play a role in gene function and development, but no specific environmental causes have yet been identified.
The theory that parental practices are responsible for ASD has long been disproved. Multiple studies have shown that vaccination to prevent childhood infectious diseases does not increase the risk of autism in the population.
Twin and family studies strongly suggest that some people have a genetic predisposition to autism. Identical twin studies show that if one twin is affected, then the other will be affected between 36 to 95 percent of the time. There are a number of studies in progress to determine the specific genetic factors associated with the development of ASD.
In families with one child with ASD, the risk of having a second child with the disorder also increases. Many of the genes found to be associated with autism are involved in the function of the chemical connections between brain neurons synapses. Researchers are looking for clues about which genes contribute to increased susceptibility. In some cases, parents and other relatives of a child with ASD show mild impairments in social communication skills or engage in repetitive behaviors. Evidence also suggests that emotional disorders such as bipolar disorder and schizophrenia occur more frequently than average in the families of people with ASD.
The mutation then occurs in each cell as the fertilized egg divides. These mutations may affect single genes or they may be changes called copy number variations, in which stretches of DNA containing multiple genes are deleted or duplicated. Recent studies have shown that people with ASD tend to have more copy number de novo gene mutations than those without the disorder, suggesting that for some the risk of developing ASD is not the result of mutations in individual genes but rather spontaneous coding mutations across many genes.
De novo mutations may explain genetic disorders in which an affected child has the mutation in each cell but the parents do not and there is no family pattern to the disorder.
Autism risk also increases in children born to older parents. There is still much research to be done to determine the potential role of environmental factors on spontaneous mutations and how that influences ASD risk. For many children, symptoms improve with age and behavioral treatment.
During adolescence, some children with ASD may become depressed or experience behavioral problems, and their treatment may need some modification as they transition to adulthood. People with ASD usually continue to need services and supports as they get older, but depending on severity of the disorder, people with ASD may be able to work successfully and live independently or within a supportive environment.
There is no cure for ASD. Therapies and behavioral interventions are designed to remedy specific symptoms and can substantially improve those symptoms. The ideal treatment plan coordinates therapies and interventions that meet the specific needs of the individual. While social and communication difficulties and unusual behaviors define ASD, affected individuals can have a wide range of intellectual abilities and language skills. A majority of people with ASD have mild to moderate intellectual disability, while others have average to above-average intelligence.
Some have particular cognitive abilities that greatly surpass their overall level of functioning, often in areas such as music, mathematics, or memory. Some people with ASD do not speak at all, while others use language fluently.
However, fluent speakers with ASD often have problems associated with verbal communication. They might speak in a monotone voice, have unusual vocal mannerisms, or choose unusual topics of conversation. Several diagnoses that used to be classified as separate conditions are now grouped together under the diagnosis of ASD.
For example, autistic disorder was a term that was used when affected individuals had limited or absent verbal communication, often in combination with intellectual disability. By contrast, Asperger syndrome was a diagnosis formerly applied to affected individuals of average or above-average intelligence who were not delayed in their language development. The broader diagnosis of ASD was established because many affected individuals fall outside of the strict definitions of the narrower diagnoses, and their intellectual and communication abilities may change over time.
However, some individuals who were previously diagnosed with one of the subtypes now do not meet all the criteria of the new umbrella diagnosis. ASD is a common condition, and the number of children diagnosed with ASD has been increasing rapidly in the past few decades. The prevalence of the disorder in the United States is estimated at 1 in 59 children. In the s, before the term ASD was used, the prevalence of autism was reported to be about 1 in 2, However, it is unclear whether this represents a true increase in the prevalence of ASD or reflects changes in the way behaviors characteristic of the disorder have been diagnosed and categorized.
Changes in over 1, genes have been reported to be associated with ASD, but a large number of these associations have not been confirmed. Many common gene variations are thought to affect the risk of developing ASD, but not all people with one or more of these gene variations will be affected. Individually, most of the gene variations have only a small effect. Genetic factors are estimated to contribute 40 to 80 percent of ASD risk.
The risk from gene variants combined with environmental risk factors, such as parental age, birth complications, and others that have not been identified, determine an individual's risk of developing this complex condition. By contrast, in about 2 to 4 percent of people with ASD, rare gene mutations or chromosome abnormalities are thought to be the cause of the condition, often as a feature of syndromes that also involve additional signs and symptoms affecting various parts of the body.
In addition to ASD and intellectual disability, this condition involves distinctive facial features and a wide variety of other signs and symptoms. In most individuals with ASD caused by rare gene mutations, the mutations occur in only a single gene. Many of the genes associated with ASD are involved in the development of the brain. The proteins produced from these genes affect multiple aspects of brain development, including production, growth, and organization of nerve cells neurons.
Some affect the number of neurons that are produced, while others are involved in the development or function of the connections between neurons synapses where cell-to-cell communication takes place, or of the cell projections dendrites that carry signals received at the synapses to the neuron.
To some, bright lights are distressing, while others will stare at bright lights for hours. Many people with autism can not stand light touch: scratchy clothing could be unbearable. Others seem immune to pain and may hurt themselves.
Mood swings are common. The Cause of Autism is Unknown It was once thought that poor parenting caused autism. Diagnosis Autism is a behaviorally defined syndrome. Treatment Although symptoms in children may lessen with age, autism is a lifelong disorder.
Abnormal brain areas in people with autism include the: Cerebellum - reduced size in parts of the cerebellum. Hippocampus and Amygdala - smaller volume. Also, neurons in these areas are smaller and more tightly packed higher cell density. Lobes of the Cerebrum - larger size than normal.
Ventricles - increased size. Caudate nucleus - reduced volume. Autism is seen more often in boys; four or five boys will have autism compared to one girl. But girls with autism are often more severely affected than boys and score lower on intelligence tests. Leo Kanner first described autism as the "inability to relate themselves in the ordinary way to people and situations from the beginning of life" in the paper "Autistic Disturbances of Affective Contact.
Some people with autism are gifted in certain areas such as math or music. Autism has also been called "early infantile autism," "childhood autism," "Kanner's autism," and "pervasive developmental disorder.
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