Autism: Autism and Fractionable Autism Triad Essay

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Jessica Cipperley March 12,2013

Autism has recently become a topic of heated discussion in both the medical and social fields. Since the diagnosis of autism has increased in the past decades, the question rises whether we are becoming more aware of the disorder, or if there are genetic or environmental influences that are to blame. There have been several studies conducted trying to answer that question, and I found a few while looking through PubMed. In the article, “A multivariate twin study of autistic traits in 12 year olds: testing the fractionable autism triad hypothesis” by Robinson and her colleagues (2011), the original idea that a triad of phenotypic characteristics of autism was caused by genetic and environmental factors was studied. Since the presentation of this idea, general population studies confirmed the hypothesis. The characteristics of autism were separated into three distinct triads, reciprocal social interaction, communication, and restricted and repetitive behaviors and interests. In this study, the researchers also refer to a general study of twins at age 7, and again at age 8. This was called the Twin Early Development Study (TEDS). These studies showed limited overlap of genetics and environmental influences between the different traits of autism. Robinson and her colleagues performed the same study but used twins at the age of 12 this time. They wondered if the results would be similar at a higher age, and also if there was a difference in the results based on the sex of the participants. Since all three traits must be present for the definition of autism, and males are diagnosed with autism more often than females, it was hypothesized that males would present more overlap of all the traits than the females. They continued a longitudinal study began in the UK with 7-year-old twins in which 75% of the participants had been confirmed twins by DNA analysis. The parents of the participants were given a yes or no survey to assess traits of autism. Of the 11,936 participants, 80 of the children were suspected to have autism spectrum disorder. In these sets of twins, the researchers studied their scores on these surveys, and found that the concordance of extreme traits were higher in monozygotic twins versus dizygotic twins. After collecting their data, the researchers were able to support the fractionable autism triad hypothesis. They found that each of the traits were 72 to 76 percent heritable in males, and 58 to 74 percent heritable in females. But twins don’t always show the same traits, and they show traits in different severities. They concluded that of the pairs of twins in which at least one showed autism traits, only 38 percent could be said to be caused by genetic factors, while 58 percent could be said to be environmentally influenced. They also concluded that each trait considered to be one of autism could be caused by different genetic or environmental factors. They decided that further research was necessary, but that there was not only one cause for autism, and one factor could not be solely blamed for the disorder. In the second article, “Characteristics and concordance of autism spectrum disorders among 277 twin pairs”, Rosenberg and her colleagues (2009) used internet-based surveys to test the link between monozygotic and dizygotic twins and the occurrence of autism spectrum traits. They outline that only 10% of autism disorder cases can be linked to an underlying medical condition. They used the Interactive Autism Network to recruit participants in their twin study. Questionnaires were posted to this online forum, and families were reminded to fill them out every 2 weeks after initially filling out their registration information. After collecting information about types of twins, the social and economic status of the family, and race, the studies began. The