Possible Causes of Low Functioning Autism
Possible contributing causes of low functioning autism include environmental toxins, genetic susceptibility, infections, ingestion of chemicals, vitamin deficiency and abnormal maternal immune responses. Certain conditions such as reduced head size at birth and later excessive increase in head size or differences in cerebral blood flow are associated with autism but are not causes. In addition, changes in diagnostic testing methods and definitions may have created "diagnostic substitution" that creates the illusion of an "autism epidemic".
Changes in Diagnostic Testing and Definitions
Since prevalence rates of autism have been rapidly growing research has focused on the etiology of autism spectrum disorders (ASD) including causes of low functioning autism. The authors of The Autism Matrix (Eyal, Hart, Oncular, Oren & Rossi, 2010) explore the historical perspective of how autism has been diagnosed during the past 70 years and suggest that many children who had been diagnosed with mental retardation in the 1950s would meet the current day criteria for autism.
With the deinstitutionalization movement of the 1960s and 1970s and the push for parents to raise their children at home with supports from early intervention and special education programs- the diagnosis of autism steadily rose as the diagnosis of “mental retardation”-or to use the current term “developmental disabilities” has dropped.
Possible reasons for diagnostic substitution are that the term “autism” carries a lesser stigma, greater hope for cure and a host of treatments designed for children with ASD. Causes of low functioning autism share the same causes that are associated with other forms of developmental disabilities, including maternal health, prenatal and peri-natal trauma, infections and environmental toxins.
According to the authors of Autism: A comprehensive Occupational Therapy Approach (Kuhaneck, and Watling; 2010), it is not uncommon for the parents of a child with an autosomal dominant autism to learn that one of them also has an undiagnosed milder form of the syndrome. Autosomal dominance means that inheriting one mutated copy of an affected gene can cause the condition. Studies have shown that the inheritance pattern of autism is complex and ASD is not attributed to any one specific genetic cause – several have been identified over the years that could be linked to the disorder.
In addition, autism is linked to other genetic developmental disorders such as Fragile X and Retts, further suggesting genetics as one of the causes of low functioning autism.
Possible Maternal, Prenatal and Perinatal Causes of Low functioning Autism
Increased risk of autism is associated with maternal smoking, low birth weight, low Apgar scores and prematurity. Maternal use of prescription drugs during pregnancy, lengthy labor and viral infection have also been reported to be associated with children with ASD. Researchers are also investigating linkage with parental age, birth order and use of fetal ultrasound.
There is an abundance of theories and controversies over possible environmental causes of low functioning autism. Perhaps the most controversial of all is whether or not vaccinations play a role as Dr. Andrew Wakefield has suggested in his book- Callous Disregard: Autism and Vaccines. Despite a large body of parental anecdotal evidence, researchers claim that there is no link between childhood vaccinations and behavioral regression, and Wakefield's infamous Lancet paper suggesting a link between autism and the MMR vaccine has been thoroughly discredited.
Other possible environmental causes of ASD include exposure to chemicals such as mercury (which had previously been used as a vaccination preservative), antibiotics and pesticides in food. In addition, researchers found relationships between autism rates and the rate of cable television growth. This correlation may be caused by the lack of time outdoors and decreased vitamin D exposure that results from watching too much television. It also reminds us that we must be careful sometimes of reading too much into epidemiological studies.
“Callous Disregard: Autism and Vaccines: The Truth Behind a Tragedy”; Andrew Wakefield; 2010.
“Autism: A comprehensive Occupational Therapy Approach”; Heather Miller Kuhaneck & Renee Watling; 2010.
“The Autism Matrix”; Gil Eyal, Brendan Hart, Emine Oncular, Neta Oren & Natasha Ross; 2010.