As science continues to decode the human genome, our knowledge of the genetic components of disease is advancing at exponential rates...There is, as far as anyone knows, no "depression gene." And no one therefore inherits depression from his or her parents.
But there is a clear genetic component of depression. Studies of twins, for example, have found that if one twin has depression, the other is much more likely to have it as well compared to non-twin siblings. "We know there is a heritable quality of both unipolar and bipolar depression," says Dr. John H. Krystal, chair of the department of psychiatry at Yale University School of Medicine and chief of psychiatry at Yale-New Haven Hospital. It is not known exactly how strong that heritable factor is, but it is estimated at somewhere between one-third and one-half of the reason someone may develop the disease.
"The genetics of depression are a very difficult area to study," he says. Blame this, at least in part, on statistics. "With other disorders, like schizophrenia or autism, you know there is a strong genetic signal, and you expect to see it, but even then you need enormously large samples to identify the genes [for those diseases]," Krystal says.
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