Focus of Discussion: Mental Health
The number of non-elderly people in the United Stated who are reporting mental health disabilities is increasing, according to a new study. Pressassociation/handout

In essence, we come into the world pre-programmed with ailments that appear later in life, such as depression, anxiety and chemical dependence, scientists concluded.

The researchers, headed by biologist Nenad Sestan of Yale University, initiated the study to track the nearly 15,000 genes that flicker on and off during brain development to create nearly 100 billion brain cells and the incalculable number of connections between them.

The study found that men and women's brains develop differently before birth, what might help explain why men and women suffer from mental illnesses at different rates. For example, about six percent of men and 12 percent of women have depression in the U.S., according to the Centers for Disease Control and Prevention. Other illnesses like schizophrenia and autism disproportionately affect men.

We knew many of the genes involved in the development of the brain, but now we know where and when they are functioning in the human brain, said Sestan in a statement from Yale. The complexity of the system shows why the human brain may be so susceptible to psychiatric disorders.

The study appeared online in the journal Nature on Wednesday.

The researchers tested post-mortem brain tissue samples from 57 people of all ages, including unborn babies. They found that over 90 percent of the genes associated with mental illness were turned on before birth, meaning the parts of the brain responsible for symptoms of mental illness had developed.

The findings are a departure from the idea that genes for mental illness turn on later in life.

It is clear that these disease-associated genes are developmentally regulated, Sestan said.

Even with the insight, how genes regulate brain development remains a mystery. Another group found that despite genetic differences across gender and ethnicities, the prefrontal cortex - the part of the brain where the most complicated cognitive functioning takes place - is structurally similar all the way down to the cell level.

Despite the vast genetic differences between people, the aggregate of all our genes makes our brains virtually indistinguishable from each other. A scientist could look at a brain tissue sample under a microscope and would not be able to tell the ethnicity or gender of the person from whom it was taken, so it is not our race or gender that accounts for our personality, intelligence, and likelihood of becoming mentally ill; it is how our genes expressed themselves while our brains were developing in the womb. Unlike what those who touted the Eugenics movement of the early 20th century thought, it is impossible to breed out all so-called imperfect human traits.

Carlo Colantuoni of the Lieber Institute for Brain Development was a co-author of the paper. He said these findings further illustrate the vast complexity of human genes and how they affect brain development.

The whole thing is kind of surprising when you put all the pieces together, Colantuoni said.

The research will appear in Thursday's edition of Nature.