An accelerated rate of Beta‐amyloid Measured with [C‐11]PiB in Down Syndrome compared to Neurotypical Populations

Background Down syndrome (DS) is characterized by a higher risk and earlier onset of beta‐amyloid (Aβ) plaque accumulation and Alzheimer’s disease (AD). The triplication of chromosome 21 containing the amyloid precursor protein (APP) gene is implicated in this process and in this study we compare the accumulation rates of Aβ between DS and neurotypical (NT) populations quantified by longitudinal [C‐11]PiB imaged at the same site to minimize experimental variation. Methods Individuals with three or more [C‐11]PiB scans spanning eleven years our site with at least one Aβ+ (global SUVR>1.40) and Aβ‐ [C‐11]PiB scan were selected. 12 of 74 DS and 15 of 246 NT participants fit these criteria. An identical imaging procedure was conducted for all participants imaged on either an ECAT HR+ or Biograph mCT PET scanner 50‐70 minutes post‐injection. Reconstructed PET images were summed and spatially normalized into template space and converted into 50‐70min SUVR images using a cerebellar grey matter reference region. Global SUVR composed of grey matter regions from the AAL atlas was used as a metric for Aβ deposition. SUVR data were fit against age with a logistic growth curve (f(t) = NS+K/(1+e(‐r(t‐t50))) to determine Aβ accumulation as subjects transitioned to Aβ+. The rate of accumulation was found using the slope of the curve at Aβ positivity threshold based on the model fit. Our model fixed NS = 1.12, the average baseline SUVR of all Aβ‐ subject scans (n = 491), and K = 1.28, the highest specific binding in any participant. Results Plotting [C‐11]PiB SUVR against age provides visual comparisons of cohorts (Fig 1) and transforming the x‐axis to amyloid chronicity (t = 0 at Aβ+) illustrates differences in accumulation rates between groups (Fig 2). The average rate of amyloid accumulation (ΔSUVR/yr) when becoming Aβ+ in the DS cohort is 0.071(0.021) versus 0.043(0.009) for NT (p = 4.31×10−4). Conclusions Aβ accumulation rate was higher in the DS cohort compared to NT. This is consistent with the additional APP gene copy in DS, and we observed an accumulation rate 65% faster in this cohort. There was a higher variability in the DS population requiring further investigation towards understanding the influence of genetic and lifestyle factors on Aβ deposition.