Dr. Kelley and a team of Mayo Clinic physicians set out to identify the characteristics and causes of dementia prior to age 45. They identified 235 individuals, ages 17 to 45, who previously had normal cognitive function and were evaluated for progressive cognitive decline at Mayo Clinic from 1996 to 2006. In one-third of patients, the dementia was caused by a neurodegenerative disorder such as frontotemporal dementia, Huntington's disease or familial prion disease. However, Alzheimer's disease was an uncommon cause. In 20 percent of patients, young-onset dementia was caused by autoimmune or inflammatory conditions such as multiple sclerosis, autoimmune encephalopathy or neuropsychiatric lupus. According to Dr. Kelley, this is an important finding, because many of these diseases may have specific treatments.

Additionally, 10 percent had metabolic disorders commonly thought to occur mainly in children. In 19 percent of the patients, the cause of young-onset dementia remained unknown despite thorough and exhaustive evaluation.

"This study sheds light on the fact that young people do, in fact, develop dementia, and that there are important differences between the causes of young-onset dementia and the causes of dementia in older individuals," says Dr. Kelley. "However, more research is required to better understand the characteristics and most effective treatments for young patients with dementia."

Brad Bishop is one of the patients who influenced Dr. Kelley to pursue this research. Bishop, age 27, was diagnosed with frontotemporal dementia in 2006. According to his parents, he was an energetic, thoughtful, caring and intelligent young man who graduated from college in 2004 with a double major in business and computers. His symptoms of dementia started around age 21, including withdrawal from people outside his family, inappropriate behavior, poor financial judgment and progressive decline in cognitive function. Now, Bishop needs around-the-clock care as his brain continues to deteriorate.

"We are seeing our son disappear before our eyes, little bit by little bit," says Susan Bishop, his mother. "We'll always hope for a miracle, but realistically we just want Brad to be safe, happy, comfortable and treated with the dignity and respect that he deserves & every day we have with him is a gift."

Dr. Kelley and his team will continue to learn more by prospectively following patients like Bishop to better understand what causes early-onset dementia. Other members of the Mayo Clinic research team included Bradley Boeve, M.D., and Keith Josephs, M.D.