Heritability of psychosis in Alzheimer disease.

OBJECTIVE: The authors have previously demonstrated familial clustering of psychotic symptoms in late-onset Alzheimer disease (LOAD+P) and sought to estimate and explore the nature of the heritability of LOAD+P. METHODS: The heritability of LOAD+P, defined by single and multiple psychotic symptoms, was estimated with data from the National Institute of Mental Health AD Genetics Initiative. RESULTS: The estimated heritability for LOAD+P defined by multiple psychotic symptoms was 61%; for LOAD+P defined by any occurrence of psychotic symptoms, it was 30%. CONCLUSION: Multiplicity of symptoms may represent a useful means for defining a genetically determined LOAD+P phenotype.