Psychotic behavior in Alzheimer's patients may be linked to genetics, according to researchers in Pittsburgh.

They reported in Neurology that in their study of 371 families where two or more members were diagnosed with "definite, probable, or possible Alzheimer's disease with psychosis," 461 siblings also were diagnosed with Alzheimer's.

"There was significant association between family members' psychosis and the occurrence of AD plus psychosis of their siblings," said Dr. Robert A. Sweet of the Alzheimer Disease Research Center, Western Psychiatric Institute and Clinic in Pittsburgh. "Among the siblings, the odds of exhibiting psychosis were more than double among siblings of (family members) who themselves exhibited psychosis."

Past studies have found that 40 to 60 percent of Alzheimer's patients suffer from psychotic symptoms including hallucinations and delusions.

These behaviors are linked to more aggressive behavior, more rapid functional decline, and early institutionalization, Sweet said, adding that Alzheimer's disease and psychosis among siblings is an important first step for future research.

"There may be a set of genes that each contribute a modest risk to psychosis across neurodevelopmental and neurodegenerative conditions," he said.

Sweet also noted, however, that early-life environmental factors which might make patients more susceptible to psychosis had not been ruled out. And although patients were assessed through interview questions and a psychiatric rating scale, validated behavioral rating scales were not used, he said, meaning there could have been an overestimate of psychosis frequency.

Other sources: American Academy of Neurology