P3‐378: EFFECT OF AGE, GENDER, ETHNICITY, COGNITION AND APOE GENOTYPE ON AMYLOID LOAD AMONG NORMAL, MCI AND MILD DEMENTIA SUBJECTS USING [F‐18] FLORBETABEN

We utilized visually rated amyloid PET scans to determine the quantitative threshold of amyloid positivity for [F-18]Florbetaben PET scans and to determine the inter-relationships among amyloid load, age, ethnicity, gender, severity of cognitive impairment and ApolipoproteinE (APOE) genotype. Two experienced raters, blinded to clinical and genetic status of the subjects, conducted visual ratings on PET scans (inter-rater reliability was 100% for amyloid positive and 93% for amyloid negative) for 152 participants (mean age 71.1 ±7.6 yrs) who were Cognitively Normal (n=46), Mild Cognitive Impairment (n=68) and Mild Dementia (n=38). Quantitative amyloid load was measured with Standardized Uptake Value Ratios (SUVRs), referenced to the cerebellar gray matter and averaged for five cortical regions (frontal, temporal, parietal, anterior cingulate and posterior cingulate). By visual rating, 10% of CN, 40% of MCI and 69% of Dementia subjects were amyloid positive. Mean SUVRs were 1.22 ± 0.16 for CNs, 1.41 ± 0.27 for MCI, and 1.59 for Dementia. Cognition assessed with the MoCA was strongly related to SUVR (p < .001). Mean SUVR was 1.56 ± 1.32 for APOEε4 genotype carriers (E4+) and 1.30 ±0.23 for non-carriers (E4-) (p< .001). There was no significant main effect for age, gender or ethnicity on SUVR. However, the following interactions were present: (1) SUVR for E4+ White non-Hispanics (WNHs) was higher than E4+ Hispanics, but E4- WNHs had lower SUVR than E4- Hispanics; (2) E4+ males had higher SUVR than E4+ females. The optimal SUVR threshold for amyloid positivity among all subjects (n=152), using ROC analyses and Youden's criteria, was 1.42 (sensitivity =94%; specificity = 92.5 %). For E4- subjects this threshold was 1.33 and 1.45 for E4+ subjects. Amyloid load was not significantly influenced by age, gender, ethnicity and cognitive status, other than the interactions between E4 status, ethnicity and gender, but was higher among E4+ than E4- subjects, as was the optimal SUVR threshold for amyloid positivity. Research studies in which quantitative thresholds for amyloid positivity are used should consider the impact of E4+ and E4- status, and the resulting clinical progression rates.