For the past five months, the Fuss family has been coping with the loss of their 17-year-old son Thomas, who died by suicide last November.

In that time, RoseMary and Daniel Fuss, both residents of Wellesley for more than 20 years, have been continuously educating themselves not only about suicide, but also about adolescent depression and mental illness in the hope of understanding what happened and why.

“We’ve been talking to a lot of professionals,” said RoseMary, whose other son, Daniel Jr., is currently a sophomore at Notre Dame. “One of the things my husband and I hoped to promote, beyond awareness and education, is what is being done with regard to research and diagnosing and treating mental illness, particularly in adolescents.”

“We can’t bring Tommy back, but we can find out whatever information might be useful for people working in this area [of mental illness in adolescents],” said Daniel Fuss. “What we’re trying to find out is what physical things, what psychological things and what environmental things contributed here.”

According to a report issued by the American Foundation for Suicide Prevention, suicide and mental illness are strongly linked, as “over 90 percent of suicide victims have a significant psychiatric illness at the time of their death.” The report also says that these illnesses are “often undiagnosed, untreated, or both.”

RoseMary said she knows from experience that diagnosing mental illness in adolescents is a very difficult and challenging process. When she first learned about the possibility that Thomas suffered from depression last spring, she said she could barely believe it.

“Tommy did not present any of the signs of depression outwardly,” she said. “He was a boy who had more friends than I will ever have in my life, he was a high honor student, he loved bowling and flag football… this was the Tommy that presented himself. His teachers felt he was happy with who he was, that he was confident and self-assured.”

“One of the really great times Tom and I had last year was the night before he died,” said Daniel. “He seemed really happy and he wanted to shoot some pool that night… we shot five games of pool, we talked and had a good time… the day he died, people remember him being particularly upbeat in school and taking careful notes in class.”

RoseMary said that Thomas, who attended the Belmont Hill School, worked to keep his depression and feelings hidden from them, even after he began going to a psychiatrist. It was only after they learned last September that Thomas had mentioned the possibility of suicide in an online chat with a friend that the family discovered just how serious his depression was.

“Our children can live in a world that we’re not privy to,” she said. “For example, Tommy never did anything that would lead us not to trust him implicitly. He was a good kid, he wasn’t involved in drugs, he wasn’t out drinking… what happened was, we missed something.”

By the time the family learned how serious Thomas’s depression was, RoseMary said, it was too late to get him properly diagnosed and treated, and he took his own life a little more than two months after his family learned that he had mentioned suicide to a friend.

“He had just started taking medication for depression the week before he died,” said Daniel. “It was a very light dosage, and it was more of a test to check for allergies.”

“It can take a very, very long time to get a mental illness diagnosed correctly,” said RoseMary. “Tommy did not give us time to get the diagnosis right. I know people who have seen doctors over a period of years before they can get the diagnosis and treatment that is appropriate.”

Daniel said that diagnosing mental illness in teenagers was especially difficult because teenagers typically go through so many difficult physical and emotional changes.

“What’s difficult here is to separate out what’s typical teenage stuff and what might be symptoms of depression,” he said. “I had ascribed some of his behavior to, ‘Well, this is what teenagers do to break away,’ but there was clearly more than that.”

After Thomas’ death, the Fuss family pledged to learn much more about adolescent mental illness and to use their knowledge to educate others about a topic they said that many people know so little about.

“There’s so much to know, and I don’t think we know enough, and the professionals don’t know enough,” said RoseMary. “But we as parents and as a community have got to work together in collaboration to take better care of our children.”

RoseMary and Daniel said that they were learning specifically about the genetics of mental illness, and also about the relation of insomnia to depression.

“One of the things we were not aware of was the issue of insomnia,” said RoseMary. “I did not know that Tommy was not sleeping through the night. In terms of things to look for, that’s clearly something that should raise a red flag.”

“Apparently, starting in the beginning of 2006, Tommy started staying up more and more at night,” said Daniel, who estimated that Thomas was getting three to four hours of sleep per night in the months leading up to his death. “I think that the lack of sleep was very serious, and it distorted some of his judgment.”

RoseMary said she and Daniel talk frequently with medical experts, particularly mental health professionals at Massachusetts General Hospital, whose Web site, www.schoolpsychiatry.org deals exclusively with adolescents and mental health. Additionally, she meets regularly with other suicide survivors to talk about their experiences.

“It’s a shared understanding of the most horrific tragedy that a parent can endure,” she said of her meetings with fellow survivors. “Everyone copes differently, and no way is right, no way is wrong. But it’s a bond that is just a shared loss that… there are no words to describe.”

When asked what advice she would give to others grappling with grief and loss, RoseMary said that she “would tell them to lean on their family, their friends and their faith.

“We have found the community to be a source of strength for us… not only Wellesley and our parish community, but the Belmont Hill community,” she said. “I encourage the families and kids to share their good memories of our children with us, because those are priceless treasures, and those are what we cling to.”