The study included families with two or more members diagnosed with definite, probable, or possible AD. The 371 "probands" or family members diagnosed with AD and accompanying psychotic behaviors, had a total of 461 siblings, also diagnosed with AD.
According to study author, Robert A. Sweet, MD, Alzheimer Disease Research Center, Western Psychiatric Institute and Clinic in Pittsburgh, PA, the study establishes that AD with psychosis (AD+P) may aggregate in families. "There was a significant association between family members' psychosis and the occurrence of AD plus psychosis of their siblings," said Sweet. "Among the siblings, the odds of exhibiting psychosis were more than double among siblings of probands who themselves exhibited psychosis."
Sibling age and age of onset of the disease were considered as part of the study but were ruled out as factors in the development of psychosis.
The presence of psychotic symptoms in AD patients is important because such symptoms are also linked to more aggressive behavior, more rapid functional decline, and early institutionalization, said Sweet. The finding of AD+P among siblings is an important first step in evaluating the genetics that may play a role, Sweet said. "There may be a set of genes that each contribute a modest risk to psychosis across neurodevelopmental and neurodegenerative conditions," he said.
The researchers did not rule out the possibility that environmental factors in the patients' early lives might make the AD patients more susceptible to psychosis.
Subjects were assessed through semi-structured interview questions, and some were rated on the Brief Psychiatric Rating Scale (BPRS). Because validated behavioral rating scales were not used in all assessments, there may have been an overestimate of the frequency of psychosis, according to Sweet.
The study was supported by research grants from the National Institute of Aging and the National Institute of Mental Health. The American Academy of Neurology, an association of 18,000 neurologists and neuroscience professionals, is dedicated to improving patient care through education and research.
For more information about the American Academy of Neurology, visit its web site at www.aan.com.