We saw in chapter 9 that susceptibility to disease is likely to be determined by defects in many genes. Autism seems to belong to that category of diseases. Autism is a neurodevelopmental disorder first recognized as a disease in 1943. It is already apparent during the first three years of life, expressed in lack of verbal communication, social responsiveness, and ritualized behavior. Autism affects approximately 1 child in 2,500.
Over the years, several theories have been put forth to explain this disease. These include behavioral, environmental, dietary, viral, autoimmune, and genetic causes. Statistical studies have shown that occurrence of autism among siblings is 2-6 percent, a value much higher than simple chance alone, which is 1 in 2,500, or, 0.004 percent. In addition, monozygotic twins show a twenty-five-fold higher concordance for autism than dizygotic twins. These results strongly suggest that autism is a polygenic trait.
An American-Australian team recently tackled the problem, this time using a total of 519 DNA markers to study 147 pairs of autistic siblings as well as their parents. They did a total of 160,000 DNAtyping experiments. The conclusions from their study are that fifteen or more genes seem to be involved in autism. These genes were
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