Harvard Mental Health Letter

Copy number variation: The new genetic frontier

A new theory about why psychiatric disorders are so heterogeneous.

Studies in identical twins suggest that autism spectrum disorders, schizophrenia, and many other psychiatric conditions are highly heritable — meaning that genes contribute to their development more than environmental factors do. In schizophrenia, for example, about 80% of disease risk is conferred through genes, while in autism spectrum disorders, 90% of risk is genetic. Yet researchers have been unable to conclusively identify the causative genes after 20 years of searching in various ways.

Traditionally, geneticists have focused on identifying single unit changes in the basic genetic code, known as single nucleotide polymorphisms (SNPs). One theory holds that SNPs, which account for most of the genetic variety between one individual and the next, may also underlie the genetic risk of various diseases, including psychiatric disorders.

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