Identical twins have the exact same genes and fraternal non-identical twins have only half of their genes in common. By examining the rates of concordance the number of twin pairs that both have autism it is possible to determine if there is a genetic component to autism. Studies that looked at the incidence of twins with autism determined that identical twins are more likely to be concordant both affected with autism than fraternal twins.
This means that individuals with the same genes both have autism more often than twins with only half of the same genes. This finding suggests that genes play a role in the development of autism. Identical twin pairs with autism reveal that there is a genetic component to autism. However, if autism was purely genetic, then all identical twins should be affected with autism concordant.
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The fact that there are some identical twin pairs that are discordant for autism one twin has autism and the other does not means that other factors, possibly environmental, must also play a role in causing autism. These discordant identical twin pairs highlight the fact that there must be other factors besides genes that also influence the development of autism. There have been speculations as to what other factors might influence or cause an individual to become autistic.
These speculations include viral, immunologic including vaccinations , and environmental factors. While there are many theories about possible causes for autism, as of no specific non-genetic causes have been found and there is no scientific evidence for any specific environmental factor being a causative agent. Much work is being done in this area. Other scientific studies that point to the role of genes in the cause of autism are studies that look at the recurrence risk for autism.
A recurrence risk is the chance that the same condition will occur for a second time in the same family. If a disease has no genetic component, then the recurrence risk should equal the incidence of the disorder. If autism had no genetic component, then it would not be expected to occur twice in the same family.
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However, studies have shown that autism does have an increased recurrence risk. The fact that the recurrence risks are increased in families with one child with autism indicates that there is some genetic component to autism. Asperger syndrome —A term used to describe high-functioning individuals with autism.
These individuals usually have normal IQ and some language skills. Pervasive developmental disorder PDD —The term used by the American Psychiatric Association for individuals who meet some but not all of the criteria for autism. Savant skills —Unusual talents, usually in art, math or music, that some individuals with autism have in addition to the deficits of autism.
While no specific gene has been found to cause isolated autism, there are some genetic syndromes in which the affected individual can have autistic behaviors. These genetic syndromes include untreated phenylketonuria PKU , Fragile X syndrome , tuberous sclerosis , Rett syndrome and others. Phenylketonuria is an inborn error of metabolism. Individuals with PKU are missing an enzyme necessary to break down phenylalanine, an amino acid found in protein rich food. As these individuals eat protein, phenylalanine builds up in the bloodstream and nervous system eventually leading to mental retardation and autistic behaviors.
The vast majority of infants in the US are tested at birth newborn screening and those affected with PKU are treated with a protein free diet. This disorder is more common among individuals of northern European descent. Fragile X syndrome is a mental retardation syndrome that predominantly but not exclusively affects males. Males with fragile X syndrome have long narrow faces, large cupped ears, enlarged testicles as adults and variable degrees of mental retardation.
Some individuals with fragile X syndrome also display autistic behaviors. Tuberous sclerosis is a variable disease characterized by hypopigmented skin patches, tumors, seizures, and mental retardation in some affected individuals. Rett syndrome is a progressive neurological disorder that almost exclusively affects females. Girls with Rett syndrome develop normally until the age of 18 months and then undergo a period of regression with loss of speech and motor milestones. In addition, girls with Rett syndrome exhibit a nearly ceaseless hand washing or hand wringing motion.
Girls with Rett syndrome also have mental retardation and can have autistic like behaviors. Many studies are underway to try and determine the etiology or cause of autism. The exact incidence of autism is not known. Because the diagnostic criteria for autism has changed and broadened over the years, studies done to determine the incidence have yielded different estimates. Using the newer, more inclusive criteria, it is estimated that one in individuals are affected with autism and that over half a million individuals in the United States fit the diagnostic criteria for autism, PDD, or Asperger syndrome.
Boys are affected three times more often than girls, giving autism a ratio of affected boys to affected girls. While boys may be affected more often, girls with autism tend to be more severely affected and have a lower IQ. The reasons for these differences are not known. Autism occurs in all racial, social and economic backgrounds. One of the most frustrating aspects of autism is the lack of physical findings in individuals with autism.
Most individuals with autism have normal appearance and few, if any, medical problems. Because the specific cause of autism is unknown, there is no prenatal test available for autism. Autism is a spectrum disorder. A spectrum refers to the fact that individuals with a diagnosis of autism can have very different abilities and deficits. The spectrum of autism stretches from a socially isolated adult with normal IQ to a severally affected child with mental retardation and behavioral problems.
The following is a partial list of behaviors seen in individuals with autism divided into main areas of concern. It is unlikely that any specific individual would exhibit all of the following behaviors. Most affected individuals would be expected to exhibit some but not all of the following behaviors.
There is no medical test like a blood test or brain scan to diagnose autism. The diagnosis of autism is very difficult to make in young children due to the lack of physical findings and the variable behavior of children. Because the primary signs and symptoms of autism are behavioral, the diagnosis usually requires evaluation by a specialized team of health professionals and occurs over a period of time.
This team of specialists may include a developmental pediatrician, speech therapist, psychologist, geneticist and other health professionals. Medical tests may be done to rule out other possible causes and may include a hearing evaluation, chromosome analysis, DNA testing for specific genetic disorders and brain imaging MRI, EEG or CT scan to rule out structural brain anomalies. Once other medical causes have been excluded, the diagnosis for autism can be made using criteria from the fourth edition of the Diagnostic and Statistical Manual of Mental Disorders DSM IV.
This manual developed by the American Psychiatric Association lists abnormal. If an individual displays enough distinct behaviors from the following list, then they will meet the diagnostic criteria for autism. Most individuals will not exhibit all of the possible behaviors listed and while individuals might exhibit the same behaviors, there is still a large degree of variability within this syndrome.
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A total of at least six items from 1 , 2 , and 3 , with at least two from 1 , and one from 2 and 3 :. Qualitative impairment in social interaction, as manifested by at least two of the following:. Qualitative impairments in communication as manifested by at least one of the following:. Restricted repetitive and stereotyped patterns of behavior, interests, and activities, as manifested by as least one of the following:.
Delays or abnormal functioning in at least one of the following areas, with onset prior to age three years:. Using these criteria, the diagnosis of autism is usually made in children around the age of two and a half to three originally seen for speech delay.
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Often these children are initially thought to have hearing impairments due to their lack of response to verbal cues and their lack of speech. While speech delay or absence might be the factor that initially brings a child with autism to the attention of medical or educational professionals, it soon becomes apparent that there are other symptoms in addition to the lack of speech. These deficits become more obvious when children with autism are enrolled in school for the first time. Their inability to interact with their peers becomes highlighted.
Behaviors such as hand flapping, temper tantrums, and head banging also contribute to the diagnosis.
Because the criteria to diagnose autism are based on observation, several appointments with healthcare providers may be necessary before a definitive diagnosis can be reached. In addition to observation, structured interviews of the parents are also used to elicit information about early behavior and development. Sometimes these interviews may be supplemented by review of family movies and photographs. Many parents find the process of diagnosing autism frustrating due to the amount of time it takes and the uncertainty of the diagnosis.
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Many health care providers hesitate to give a diagnosis of autism and use other terms as a means of protecting the family from what they perceive to be a devastating diagnosis. While meaning well, this strategy usually increases frustration and only ultimately delays the diagnosis. The delay in diagnosis can lead to a delay in treatment and in a worse case scenario a denial of services especially if another term is used.
There is no cure for autism. However, autism is not a static disorder. Behaviors can and do change over time and educational treatments can be used to focus on appropriate behaviors. The treatments available for individuals with autism depend upon their needs, but. While treatments vary and there is considerable controversy about some treatments, there is uniform agreement that early and intensive intervention allows for the best prognosis.
Studies have shown that individuals with autism respond well to a highly structured, specialized education program tailored to their individual needs.