Up to two hundred genes can be implicated in autism, and some evidence suggests that you need several to manifest the syndrome. Sometimes, epistatic, or modifier, genes influence the expression of primary genes; sometimes environmental factors influence the expression of these genes. The closer the relationship between genotype and phenotype, the easier it is to discern. In autism, some people with a share genotype don't share a phenotype, and some with a shared phenotype don't share a genotype.
( Andrew Solomon )
[ Far from the Tree: Parents, ]
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