By the time Jacob Flood turned 2, his mother, Marla Flood, knew something about him was different.
"It was pretty much said, you know, 'He's splitting off. He's splintering off, developmentally," Flood said. "'I think he has autism.' And, of course, mom didn't take that very well."
Watch the second part of the gene series tonight on "World News with Charles Gibson."
Within a year, Jacob was put on medication for his autism. But over the years, his behavior only seemed to get worse.
"He would get to the point where he was extremely physically aggressive towards myself, my husband, my kids. He would bite, pinch, pull hair. He would hit," Flood said.
Flood, her husband and other children ended up with bruises on their arms.
Prescribing the right drugs was a "guessing game," she said, because Jacob isn't able to communicate well. "He can't tell me when 'this medicine is making my body shaky, or it's giving me a headache, or it's making me feel like I'm going to throw up.'"
So, two years ago, Jacob's doctor tried something new and innovative. Jacob, who is now 11, was given a genetic test to find out how his body was processing the autism medicines he was on.
The results were startling.
"We realized we overdosed him," said Dr. Patty Manning-Courtney, of Cincinnati Children's Hospital Medical Center, "and he got worse, because we gave him too much of what we thought was a good thing."
Cincinnati Children's Hospital currently offers testing for two genes to all children and adults admitted to the hospital who receive psychiatric medicines.
The test involves gauging the way individual people's livers metabolize medicines.
And Jacob's mother said that while the new lower-dose prescription did not cure her son's autism, he's now a "different kid."
"We saw a big change. We saw less aggressiveness," Flood said. "He still screams, and he stills get mad, and he still has some aggressive behaviors, but they're nothing like they were before."
Right now, pharmacogenetics, as the field is called, is in its infancy. Only certain hospitals offer the kind of testing Jacob received to help doctors tailor treatment for individual patients. But eventually, doctors hope the practice will spread.
"I do envision in the next five to 10 years, the number of genes we'll test will grow immensely, and the number of opportunities for patients to get more personalized care, will grow immensely," said Dr. Tracy Glauser, co-director of the Genetic Pharmacology Service at Cincinnati Children's Hospital.
At Duke University in North Carolina, doctors are running a cutting-edge experiment. They are analyzing the DNA of individual cancer tumors to determine the best type of chemotherapy regimen to use in fighting that particular person's lung cancer.
As many as a quarter of lung cancer patients may be resistant to standard chemotherapy, experts say.
"We know that for people with advanced lung cancer our standard treatment is a combination of a platinum drug plus another type of chemotherapy. Unfortunately, we don't know for each individual patient, which drug combination is going to work best," said Dr. Jennifer Garst, associate professor with the Albert Thoracic Oncology Program at Duke University Health Systems.