Mental perception extremes stemming from duplication or deletion of genetic code

Autism and psychotic-affective disorders are developmental opposites, two sides of the same coin – according to the theory developed by researchers Bernard Crespi (a geneticist at Simon Fraser University, Canada) and Christopher Badcock (a sociologist at the London School of Economics) that the brain’s balance is set by a “tug of war” between our genes.

Their theory proposes that an epigenetic disruption results in either:
(a) under-development of the ‘social’ brain, which is linked to autism; or
(b) over-development of the ‘social’ brain, which results in psychotic-affective conditions such as schizophrenia, bipolar disorder and depression.

The extremes of these disorders – autism to schizophrenia – are up to 80% heritable and expressed by DNA copy-number variants – that is, the number of copies of each region of human DNA, which is ordinarily diploid: having two copies, one per chromosome. However, this varies for particular DNA regions due to deletion or duplication of the genetic code leading to disorders such as under or over development of the “social” brain.

Nature Medicine reports in its April issue that research by Crespi has found that five sections of DNA with copy-number variants were associated with both extremes, and of these sections, four acted in opposite directions. That is, for some of these copy-number variants:
(i) too many copies were associated with autism, and
(ii) too few with schizophrenia, or vice versa depending on the actual variant.

Why does the deletion or duplication occur?

DNA matched copy-number variants were uncovered with completion of the human genome project, which enabled observation of disorders such as:
(c) cancer – where the level of duplication was found to be elevated; and
(d) lupus and other inflammatory autoimmune disorders were associated with deletion.

This deletion or duplication may have an epigenetic origin.

Gene expression can be altered by non-genetic factors causing the organism’s genes to “express themselves” differently depending on the cell’s memory. For example, a famine three generations ago in males giving rise to trans-generational epigenetic expression of lower heart disease and diabetes compared to a control population.

This recent work by Bernard Crespi and Christopher Badcock has tied genetics, psychiatry and perception in a unified fashion.

A meeting of minds Nature Medicine 16, 353–355 (2010)


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