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The five psychological disorders, autism, attention deficit-hyperactivity disorder (ADHD), bipolar disorder, major depressive disorder, and schizophrenia, have a genetic link to one another, which can explain why certain mental illnesses tend to run in families. According to a new study published in the medical journal Lancet, researchers found that each of these diseases share a biological base.

"There were several regions of the genome, several variations that seemed to increase the risk for all five. It's important to realize, of course, that this is a small part of the genetic component of these disorders, but it points to a shared biology," one of the head researchers, Dr. Jordan Smoller, MD, ScD said to CBS. Dr. Smoller is from the Massachusetts General Hospital in Boston.

According to the international group of researchers, singular nucleotide polymorphisms (SNPs), which are DNA sequence variations, in two genes responsible for calcium-channel activity were linked to all five mental disorders. More specifically, the SNPs that were found in four regions were present in the genetic makeup of the five mental disorders. These regions included two on chromosome 10, one on chromosome three, and a calcium-subunit on chromosome 12. The calcium-subunit gene has already been traced to bipolar disorder, schizophrenia, and major depressive disorder from previous findings. The researchers analyzed data from 33,332 cases with 27,888 controls. This data set may be the largest genetic study related to psychiatric illnesses as of yet.

Although Smoller admitted that the genetic link between all five disorders might play a small role, the fact that these disorders share any similarities in their manifestations is important. One of the more significant inferences from the study is that genetics "can contribute to prediction and prevention of psychiatric diseases, along with the identification of molecular targets for new generations of psychotropic drugs."

The research from this study will hopefully be the first steps in improving understanding of how psychiatric illnesses start. By understanding the genetic links between diseases, there might be different ways of improving treatments for all mental disorders.

The National Institute of Mental Health funded the study.  Government grants from other countries and grants from the National Institutes of Health (NIH), as well as private and foundation support also contributed.