Parkinson’s Relatives Face Increased Risk of Cognitive Impairment or Dementia

Immediate relatives of people who have Parkinson’s disease are at greater risk of developing cognitive impairment or dementia than people who have no first-degree relatives (brother, sister, mother, father, son or daughter) with Parkinson’s disease, according to a new study by Mayo Clinic. The risk is particularly increased for relatives of patients who developed Parkinson’s disease before age 67.

This is one of the first large population-based studies to show that Parkinson’s disease and cognitive impairment or dementia may share familial factors that make a person susceptible to developing one or both disorders. In addition, the study is a major methodological departure from previous attempts to study the risk of cognitive impairment or dementia in families with Parkinson’s disease. It is based on the “family study” method. Researchers assessed each relative separately for cognitive status instead of using only one family member to provide information for the full family. The Mayo Clinic report appears in the October 2007 issue of the journal Archives of Neurology. Walter Rocca, M.D., is lead author of the study and a Mayo Clinic neurologist and epidemiologist who specializes in the study of neurological diseases in the population. “Because the evidence for increased risk of dementia in relatives of patients with Parkinson’s disease was conflicting, we set out to clarify it,” says Dr. Rocca. “We show that cognitive impairment or dementia may share familial susceptibility factors with Parkinson’s disease – which means that if a person is susceptible to developing Parkinson’s disease, the same susceptibility factors may predispose the person to cognitive impairment or dementia.” Dr. Rocca emphasizes that the familial susceptibility factors may be genetic or may be nongenetic, such as shared diet in the family. Further research is needed to determine susceptibility factors. The Mayo Clinic team studied:

1. 1,019 first-degree relatives of 162 patients with Parkinson’s disease from Olmsted County, Minn., where Mayo Clinic’s Minnesota campus is located
2. 858 first-degree relatives of 147 “matched controls” from the same Olmsted County population – the controls were similar in age and sex to the patients in the first group, but did not have Parkinson’s disease
3. 2,716 first-degree relatives of 411 patients with Parkinson’s disease who were referred to Mayo Clinic from a broader area, including Minnesota, Iowa, Wisconsin, North Dakota and South Dakota

For each group, researchers administered via telephone a cognitive test to relatives. If a relative was deceased or unavailable, researchers administered via telephone a brief dementia questionnaire to a close family member. If the family member reported that the relative had dementia, Mayo Clinic researchers obtained a copy of the medical record to confirm the diagnosis. Researchers had access to extensive documentation of dementia from medical records archived at Mayo Clinic. The sample group studied included both patients with Parkinson’s disease who lived in the local county and those who were referred to Mayo Clinic. Several intriguing leads prompted the researchers to hypothesize the existence of familial shared susceptibility factors for Parkinson’s disease and cognitive impairment or dementia. One was that dementia tends to occur in patients who have Parkinson’s disease, and there is some suggestion it may be due to shared susceptibility genetic variations such as those in the apolipoprotein E gene. Another lead was that both conditions cause lesions on the brain that disrupt normal brain function. In Alzheimer’s disease, these lesions are called plaques and tangles. In Parkinson’s disease, the lesions are called Lewy bodies. It is thought that these brain lesions may share common risk factors. Other members of the Mayo Clinic team included: James Bower, M.D.; J. Eric Ahlskog, M.D., Ph.D.; Alexis Elbaz, M.D., Ph.D.; Brandon Grossardt; Shannon K. McDonnell; Daniel J. Schaid, Ph.D.; and Demetrius Maraganore, M.D. Their work was supported by two grants from the National Institutes of Health. (Source: Archives of Neurology : Carol Lammers : Mayo Clinic : December 2007)