This study will perform a targeted metabolic analysis in blood and urine samples from subjects attending the Baylor AT&T Memory Center. The aim is to identify novel biomarkers that can distinguish normal aging subjects with no cognitive impairment from those with mild, moderate or severe cognitive impairment associated with Alzheimer's disease. Subjects will also be screened for B-vitamin deficiencies that may correlate with other metabolic biomarkers and Alzheimer's disease.

All subjects will be clinically assessed using standard measures of clinical care. Cognitive function will be assessed by the Montreal Cognitive Assessment (MoCA). Disease severity will be assessed by the Clinical Dementia Rating Scale (CDR). Social function will be assessed by the Functional Activities Questionnaire (FAQ). Based on clinical assessment, subjects will be classified into one of the following groups.

1. Normal (Spouse or Caregiver)
2. Mild cognitive impairment
3. Alzheimer's disease A. Mild B. Moderate C. Severe

The investigators plan to enroll 60 subjects in each group from 1 and 2; 40 subjects in each of the groups 3A and 3B and 20 subjects in group 3C.

Inclusion Criteria:

A. Both Males and females B. Patients at least 40-years of age C. Mild Cognitive Impairment D. Alzheimer 's disease

1. Mild
2. Moderate
3. Severe

Exclusion Criteria:

A. No recent major surgery within the last 6 months B. Free of any malignant disease C. No chronic renal disease D. No other major neurodegenerative disorders (i.e. Parkinson's disease, multiple sclerosis)

The investigators will aim to consent male and female subjects that are attending the Baylor AT&T Memory Center. Patients will be under the care of Dr. Cindy Marshall and Dr. Claudia Padilla.