The purpose of this clinical research study is to determine if a specific genetic allele is involved with the development of agitation in patients with late-onset Alzheimer's Disease (AD). The study will compare the results of genetic testing between two groups: individuals with late-onset AD who show signs of agitation and individuals with late-onset AD who do not show signs of agitation.

Agitation and other behavioral disturbances are a main cause in the need for increasing levels of care for the patient with Alzheimer's disease (AD). And while the pathology of dementia has been studied in great detail, the etiology is considered multi-factorial. The hypothesis behind this clinical study is that the presence of the apo lipoprotein E4 (APO E4) allele will serve to predict which patients with late on-set AD are at greater risk to develop agitation.

Inclusion Criteria:

• Men and women who are at least 65 years of age
• Meet the DSM-IV-TR criteria for late-onset Alzheimer's Disease (AD)

Exclusion Criteria:

• Unable to provide informed consent or do not have a legally acceptable caregiver and/or representative present or available to enter into the informed consent process on the study subject's behalf
• Diagnosis of a non-Alzheimer's type of dementia
• Determined by the Principal Investigator (or his designee) that the study subject would be unsuitable for study participation

Patients with a diagnosis of probable Alzheimer's Disease (late-onset)