Types of Pervasive Developmental Disorders
Autism and other ASD's are included in a general category of disorders called the pervasive developmental disorders (PDD's). Of the five PDD's, three are ASD's: classic autism, Asperger syndrome, and PDD-NOS ("pervasive developmental disorder not otherwise specified," also known as atypical autism). The other two are Rett syndrome and childhood disintegrative disorder. Each of these is defined by developmental delays that affect a person's behavior and social interactions to varying degrees.
Classic autism, as described extensively above, is characterized by difficulties with social interactions. Both verbal and non-verbal communication is affected, usually resulting in delayed development of language skills. Restrictive, repetitive, or ritualized behaviors are common, as are sensory disturbances.
Asperger syndrome is a type of autism in which language development is normal, but the fundamentals of social interactions are not entirely grasped. Those with Asperger syndrome tend to be socially awkward and have difficulty reading cues from others, including facial expressions and body language. They may not bother making eye contact or using conversational gestures, but they typically show above-average intelligence and may have an unusually sophisticated vocabulary at a young age. The restricted interests and repetitive behaviors associated with classic autism must also be present for a diagnosis of Asperger syndrome.
A diagnosis of PDD-NOS is typically reserved for children with developmental disorders common to autism that do not fully meet the requirements for the medical diagnosis of autism. The symptoms may be milder, for example, or there may be an insufficient number of them to classify the disorder as autism.
Children with Childhood Disintegrative Disorder initially develop normally, but begin to fall behind or regress in various functional areas between the ages of two and ten. Following onset of this disorder, children may lose motor skills, play skills bowel and bladder control, social and self-care skills, expressive language, and receptive language skills. Should two of these six symptoms emerge in addition to two symptoms of classic autism, the diagnosis is childhood disintegrative disorder.
Rett syndrome is a PDD that affects girls almost exclusively. Initially, the symptoms are subtle, but similar to early autism symptoms. Language development is delayed and social interactions are weak, as the child neglects eye contact and is unresponsive. Repetitive behaviors such as hand-wringing, flapping, and tapping begin to emerge as the child gets slightly older. Physical developmental problems, including small hands, feet, and head size also become noticeable. Eventually, the child may lose the ability to speak, walk, and more severe physical problems, such as scoliosis, may develop. Cognitive disabilities are also quite common with Rett syndrome.
Causes of Autism
Though specific genes involved in the development of autism have not been identified, research suggests a strong genetic influence. Autism also frequently co-exists with other genetic disorders, such as fragile X syndrome, which causes mental disabilities and physical abnormalities in addition to symptoms typical of autism. Tuberous sclerosis, a genetic condition in which benign tumors grow in the brain, also has symptoms similar to those of autism and other PDD's. Tourette syndrome and attention-deficit hyperactivity disorder (ADHD) are sometimes diagnosed with autism, as well.
Examinations of autistic brain patterns and structures suggest that the disorder affects many different parts of the brain. The weight and volume of autistic brains are greater than those of non-autistic brains, possibly due to excessive neuronal development. Such "overconnectivity" in localized parts of the brain may explain some of the unusual behaviors, hypersensitivities, and other irregularities in the way that autistics respond to and interpret the world. These responses may also be due to imbalances in the chemical signaling in the brain. Serotonin, a neurotransmitter involved in controlling mood, body temperature, appetite, metabolism, and other activities, is found in higher concentrations in the autistic brain. Whether this has any impact on the symptoms is unclear, though it may present another layer or distortion that disrupts normal development. Critical aspects of brain development may be disturbed soon after conception, suggesting that prenatal environmental factors, such as toxins encountered early during pregnancy, may potentially contribute to autism.
There has been much news recently regarding a possible link between autism and vaccination of babies. Thimerosal is a mercury compound that has been used since the 1920's as a preservative in vaccines to prevent bacterial contamination. Review of its use began in the 1990's, as the FDA, NIH, and other health organizations conducted assessments of all mercury-containing foods and drugs. Ultimately, they concluded that while the mercury levels were higher than typically deemed safe for infants, it was unclear that they had any toxic consequences. With the support of the CDC and others, it was concluded that thimerosal use should be minimized until further studies could be performed and verify its safety.
By 2001, thimerosal was eliminated from childhood vaccines in the U.S. and it has continued to be a subject of intense research for many years now. An immunization safety review board commissioned by the CDC recently concluded that there is no causal connection between thimerosal. The scientific consensus is that autism research should pursue other, more likely avenues. Given that autism rates have continued to climb despite the removal of this mercury compound from vaccines, it is clear such environmental factors contributing to autism have yet to be determined.
Risk Factors of Autism
Autistics have a normal life expectancy, but are prone to several complications related to their symptoms. Due to the problems that autistics have with social interactions, they may find it difficult to make or maintain friendships. Children may have particular difficulties dealing with other children, since their playmates may not understand why they behave differently. For love and affection, they will rely upon others being patient, understanding, and receptive to the child's unusual needs.
Learning disabilities are also quite common among autistics. The cognitive difficulties are likely due to both abnormal brain development and issues with communication. A child unable to process information from the world around them in the typical way is highly unlikely to respond to standard educational approaches. The quality of communication the autistic child is capable of will define, in large part, the progress they make socially and intellectually.
Autistic children that have restrictive diets may be at risk for additional health problems, should they not get the essential vitamin, minerals, proteins, and other nutrients they need. Nutritional deficiencies may worsen chemical imbalances in the body and delay physical and mental development that would have been otherwise unaffected by autism.
Extremely repetitive or self-injurious behaviors can also be problematic for autistics. In cases where these symptoms are severe, it may be too dangerous for the autistic to be left unattended. Some also develop aggressive behaviors during tantrums, which become more dangerous as they enter adulthood.
Some autistics also develop mood disorders, depression, anxiety, and even psychosis. In some cases, these develop if the person becomes aware they are different, potentially causing them sadness, frustration, and grief. It is also conceivable that these result from chemical imbalances in the brain, perhaps connected in some way with those that contribute to autism (if imbalances are indeed responsible).
Epilepsy develops in approximately one third of autistics by the time they reach adulthood. It is unclear why, but one of the explanations for autism is defective production of synaptic proteins, which are vital for signaling in the brain. Disruptions in synaptic development have also been implicated in epilepsy, which may account for the frequency with which it coincides with autism.
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Article Last Updated: 06/26/2009