(TUCSON, Ariz.) -- Jared Lee Loughner's defense team is delving into his family's medical history, possibly looking for evidence of mental illness.
Loughner, who faces 49 charges stemming from the Tucson, Arizona shooting spree that killed six people and injured 13 others, has been diagnosed with schizophrenia -- a chronic, severe disabling brain disorder that has a significant genetic component. And in a move that could bolster his defense, Loughner's lawyers have subpoenaed public health records from 22 of his maternal relatives dating back to 1893, The New York Times reported.
"If there are a lot of people who have a schizophrenia diagnosis in his family, that does sort of add weight to the issue that this kid was at a huge genetic risk," said Dr. Charles Raison, associate professor in the department of psychiatry and behavioral sciences at Emory University School of Medicine in Atlanta. "It could have emotional effect on a jury. It could heighten the sense that this was not his fault."
Loughner's mental health has been the subject of much attention since his arrest in the Jan. 8 shootout at a constituent meet-and-greet with Rep. Gabrielle Giffords, who sustained a gunshot wound to the head, but miraculously survived. A court-ordered psychiatric evaluation concluded that 22-year-old Loughner has delusions and hallucinations -- psychotic symptoms that can distort a person's perception of reality.
"We know that psychotic illnesses run in families," said Raison, adding that the genetic contribution to mental illness can be as high as 70 percent, depending on the diagnosis. "People with schizophrenia are often related to other people with schizophrenia and to people who are odd or isolative...It's not a specific disease state that's inherited; it's this vulnerability to have this sort of odd behavior or odd way of thinking."
In May, a federal judge deemed Loughner mentally unfit to stand trial. But it's his mental state at the time of the attack that will determine his sentence.
"The only way to really assess what role psychosis played in his actions is for him to be able to explain what he thought he was doing," said Raison, adding that psychotic people tend to have a logical rationale for their delusional thought process. "No matter how bizarre the reasoning is, it makes sense. We don't believe it, but it makes sense."
Loughner has been forced to take antipsychotic drugs during his stay at a federal psychiatric facility in Springfield, Missouri, and a hearing scheduled for Sept. 21 will determine whether his mental state has improved enough for him to participate in his defense.
Copyright 2011 ABC News Radio